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Climate change and the New Zealand marine environment
Photo: Rod Budd
NIWA Client Report: NEL2007-025 October 2007 NIWA Project: DOC08305
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Climate change and the New Zealand marine environment T.J. Willis* S.J. Handley F.H. Chang C.S. Law D.J. Morrisey A.B. Mullan M. Pinkerton K.L. Rodgers P.J.H. Sutton A. Tait
Prepared for
Department of Conservation
NIWA Client Report: NEL2007- 025 October 2007 NIWA Project: DOC08305
*Trevor J. Willis National Institute of Water & Atmospheric Research Ltd Email: [email protected] 217 Akersten St, Port Nelson P O Box 893, Nelson, New Zealand Phone +64-3-548 1715, Fax +64-3-548 1716 www.niwa.co.nz
Contents Executive Summary iv
1. Introduction 1 1.1 Preamble 1 1.2 New Zealand’s ocean in a warming world. 1 1.3 Current work to update these scenarios 5
2. Sea level rise 6 2.1 Projected effects 7 2.2 Vulnerable habitats and species 8 2.2.1 Estuaries and wetlands 8 2.2.2 Mangroves 9 2.2.3 Rocky intertidal habitats 10 2.2.4 Shallow subtidal reefs 11 2.2.5 Open coast sand beaches 12
3. Wind and rainfall patterns 12 3.1 Projected effects 14 3.2 Vulnerable habitats and species 14 3.2.1 Estuaries and soft sediment communities 14 3.2.2 Mangroves 15 3.2.3 Subtidal rocky reefs 15 3.2.4 Intertidal coastlines, animals and seabirds 16
4. Ocean acidification 17 4.1 Projected effects 17 4.2 Vulnerable habitats and species 18
5. Current patterns and ocean warming 23 5.1 Projected effects 25 5.2 Vulnerable habitats and species 28
6. Indirect effects 29 6.1 Primary production 29 6.1.1 Carrying capacity 29 6.1.2 Primary production around New Zealand 29 6.1.3 Global primary production 30 6.1.4 General conclusions 32 6.2 Algal blooms 33 6.2.1 Observations of short-term ‘climate change’ on algal blooms 33 6.2.2 Projected climate effects on algal blooms in New Zealand 36
6.3 Vulnerability to invasive species 37 6.4 Vulnerability to disease and parasites 38
7. Potential indicators 38 7.1 Sea level 39 7.2 Wind and rainfall 39 7.3 CO2 and acidification 40 7.4 Ocean warming and currents 41
8. Research gaps and priorities 41 8.1 Summary of future work needed to improve climate modelling
predictions at varying spatial and temporal scales 41 8.2 Ocean warming and currents 43 8.2.1 Models 43 8.2.2 Observations 43
8.3 Mitigation of anthropogenic impacts to build resilience to climate change 44
8.4 Prediction of the effects of climate change – key questions 46
9. Conclusions 49
10. Acknowledgements 53
11. References 54
12. Appendix 1: Projected climate change over the New Zealand landmass 76
Reviewed by: A.B. MacDiarmid Approved for release by Don
Robertson:
Climate change and the New Zealand marine environment iv
Executive Summary
The Intergovernmental Panel on Climate Change (IPCC) released its Fourth Assessment Report in
2007, which updates previous efforts to predict the effects of climate changes at a global level. The
documents forming that assessment provide a useful summary of global climate trends, but do not
provide detailed advice at regional levels. Reasons for this are highlighted in recent reviews on climate
change in Australia, which illustrate the lack of many basic tools with which to make specific
predictions at scales at which appropriate management measures can be taken. This stems from three
main gaps in marine ecological research: 1) the lack of long-term time series of data to establish
correlations with past environmental fluctuations; 2) a limited understanding of the way ecosystems
are structured by interactions between species and the environment; and 3) little information on the
tolerances of habitat-forming species to variability in the environmental factors that may be affected
by climate change.
Marine systems may be impacted by a number of physical variables that are likely to interact in
inconsistent ways. The system responses will be further complicated by biological interactions among
species. These factors, coupled with the broad range of possible outcomes of model predictions, lead
to considerable variance in opinion as to the seriousness of climate change effects in the short- to
medium term. For example, it has been suggested that changes in regional oceanography will have
either little effect on current systems in northern New Zealand, or that spin-up of the South Pacific
gyre could strengthen the East Auckland Current considerably. Similarly, acidification effects in the
Southern Ocean and Sub-Antarctic waters off southern New Zealand, brought about by the increased
uptake of CO2 may have either negligible effects, or potentially disastrous effects on productivity,
community structure and biodiversity. These inconsistencies arise primarily from a lack of data,
particularly time series, and understanding with which to refine predictive models.
Some broad-scale research questions that need to be addressed in the New Zealand context to provide
impact scenarios over the next century and beyond include:
• Which species are most at risk, and consequently, which functional groups and
ecosystems are most sensitive? How will their populations change?
• What is the range of natural variability in physical and biogeochemical systems at the
present time?
• How will climate change/variability influence biodiversity, assemblage structures, and
abundance of the key participants in biogeochemical processes, and how will these change
ecosystem function?
Climate change and the New Zealand marine environment v
• What are the natural tolerances of key species and/or major taxonomic groups to changes
in various predicted stressors to provide scenarios in impact prediction?
• How will climate change influence the rate of arrival, establishment and spread of non-
indigenous species?
• What are the rates of change in key ecosystems and what adaptive potential do key groups
have to varying rates of change?
• What interactions might occur between climate-related stressors and the energetic budgets
of marine species and ecosystems?
• What is the magnitude of potential effects of climate change compared to other
anthropogenic effects on New Zealand marine ecosystems?
• How might existing sources of anthropogenic disturbance interact with projected climate
changes to exacerbate problems?
• How vulnerable are New Zealand’s economic activities in the marine environment –
especially wild fisheries, aquaculture, and tourism – to climate change in the short to
medium term?
Research priority should be given to initiating long-term monitoring studies for those oceanographic
features for which data are currently lacking, and for characterising biological assemblages and their
natural variability at a national scale. Such a programme is open-ended by nature and does not have
specific goals, and thus will not meet the criteria usually imposed for short-term research funding. It
is, however, imperative to possess such data if shorter-term experimental work is to be validated, and
to interpret the changes brought about by climate change so that effective management interventions
can be implemented, where warranted. Time series data in the natural environment usually do not
begin to have predictive power before at least ten years have elapsed, but do provide information that
forms the basis of more specific experiments of shorter duration. Predicted climate changes over the
next few decades are relatively small, and thus are difficult to simulate effectively in manipulative
experiments. A first step would be to collate and coordinate existing monitoring and measurement
programmes with a view to identifying critical gaps.
Priority for short-term experimental work is likely to be driven by feasibility, but should be
concentrated on determining the effects of likely known impacts (e.g., temperature, salinity, pH,
sedimentation) on influential taxa within different biomes. Identification of these taxa is critical to
progress in determining future ecosystem-wide effects of incremental changes in climate.
Climate change and the New Zealand marine environment vi
Given the current information void, projections of socioeconomic impacts in New Zealand as a result
of climate change could vary from serious, if major biogeochemical processes fail and/or if ocean
productivity is affected causing fishery collapses and reduced aquaculture production, to negligible.
Climate change and the New Zealand marine environment 1
1. Introduction
1.1 Preamble
This report forms a summary of the likely expected changes to the New Zealand
environment under Intergovernmental Panel on Climate Change (IPCC) scenarios, and
describes some of the potential effects on the marine environment. There has been
little research specific to marine effects of climate change undertaken in New Zealand
to date, and the report therefore uses existing information from New Zealand and
elsewhere to infer general trends, and highlight areas where knowledge is lacking.
The marine climate drives a complex series of interacting elements that dictate
biodiversity, species distributions, productivity and ecosystem function, including
biogeochemical processes across varying spatial scales (Figure 1). Changes that are
occurring and are expected to continue due to human activities are increases in
atmospheric CO2 levels and removal of atmospheric ozone. The latter has already
increased the levels of ultraviolet radiation in New Zealand, and the former has the
dual effects of causing large-scale warming (due to the greenhouse effect) and
increasing the quantity of CO2 taken up by the world’s oceans. Warming will have
effects not only on sea temperature, but also may potentially disrupt or modify
existing weather patterns. CO2 uptake has the direct effect of acidifying seawater, with
potentially consequent effects on the productivity of many marine systems.
Here, we attempt to use overseas and New Zealand examples to identify the likely
effects of four main consequences of climate change on the New Zealand marine
environment: sea level rise, changes to wind and rainfall patterns, ocean acidification,
and current patterns and ocean warming. These factors will give rise to other indirect
effects that are summarised briefly. We put forward suggestions for research
directions that may prove fruitful in the future for predicting and mitigating specific
impacts, and also suggest potential indicators for assessing the rate at which climate
change effects are being felt.
1.2 New Zealand’s ocean in a warming world.
Much of the information presented here is taken from the Climate Change Effects and
Impacts Assessment guidance manual for local government in New Zealand (MfE
2004a, b), which was published by the Ministry for the Environment. That report used
the best available information to provide projections of future climate change around
Climate change and the New Zealand marine environment 2
New Zealand, and information on how these compare with present climate extremes
and variations.
Figure 1. Schematic diagram of direct and indirect consequences of climate change in the marine environment. Green boxes are causal agents that are directly influenced by climate change.
Climate change and the New Zealand marine environment 3
The New Zealand projections are based on global climate model (GCM) projections
presented in the Intergovernmental Panel on Climate Change (IPCC) Third
Assessment Report (2001) (see Chapter 9, Cubasch et al. 2001), using 35 different
future emissions pathways or 'scenarios', described in the Special Reports on Emission
Scenarios (SRES) for the IPCC. All the SRES scenarios project ongoing increases in
the atmospheric concentration of greenhouse gases over the coming century (even
those scenarios where the emissions start to decrease at some point before 2100). The
projected global temperature increases from all scenarios over the next 50 to 100 years
are much larger than those that have occurred over the past 1000 years. The IPCC
does not contend that any one SRES scenario is more likely than any other - it is as if
they have provided a die for predicting future conditions with 35 equally-weighted
sides.
These GCM projections have been statistically down-scaled for New Zealand based
on work presented in Mullan (2001a). Using these techniques, climate projections for
New Zealand have been prepared for changes from 1990 to 2020-2049, and from 1990
to 2070-2099. These future 30-year periods are centred around 2035 and 2085, and
are referred to in this chapter as the '2030s' and '2080s' respectively. A range of
possible values for each climate variable (temperature, rainfall, etc) is provided (Table
1, Appendix 1 Fig. A1–A6). This reflects not only the range of greenhouse gas futures
represented by the 35 SRES scenarios, but also the range of climate model predictions
for individual emission scenarios. Like the IPCC, we are unable to indicate a most
likely value from within the projection range. However the extreme ends of the
ranges may be slightly less likely than the central values, since they generally result
from the one climate model which gives the most extreme projection, rather than
reflecting agreement between a number of models.
The lowest and highest rainfall projection patterns show a strong southwest to
northeast gradient: the rainfall changes in the southwest of the country vary from no
change (or a slight decrease) to a large increase in annual mean, whereas northeastern
areas vary from a large decrease to no change. There is a lot of variability among
models, and for many locations even the sign of the rainfall change cannot be stated
with any confidence. However, in the 2080s annual mean (Figure A4), the regions of
Taranaki, Manawatu-Wanganui, West Coast, Otago and Southland tend to show
increased rainfall for all scenarios, compared to Hawkes Bay and Gisborne which
show rainfall decreases for all scenarios. Seasonally, the largest decreases occur in the
north and east of the North Island in spring.
Climate change and the New Zealand marine environment 4
Table 1. Summary of the main features of New Zealand climate change projections for 2030s and 2080s. Degree of confidence on projections indicated in brackets (VH = very high, H = high, M = medium, L = low). 'Very high' confidence means that it is considered very unlikely that these estimates will be substantially revised as scientific knowledge progresses, while 'low' confidence means it is possible that estimates will be revised considerably in the future.
Climate variable
Direction of change Magnitude of change Spatial and seasonal variation
Mean temperature
Increase (VH) Mid-scenario 0.5-0.7°C by 2030s, 1.5-2.0°C by 2080s (M)
Strongest warming in winter, tendency for slightly more warming in E and N
Daily temperature extremes (frosts, hot days)
Fewer cold temperatures and frosts (VH), more high temperature episodes (VH)
Unknown Large decreases in number of frost days in lower N Island and the S Island. Substantial increase in number of days above 25°C particularly at already warm northern sites
Mean rainfall Varies around country. By 2080s Taranaki, Manawatu-Wanganui, West Coast, Otago and Southland show increases; Hawke's Bay Gisborne, eastern Canterbury, eastern Marlborough show decreases (M)
Substantial variation around the country (see Appendix 1)
Tendency to increase in south and west, decrease in N and E. Largest projected seasonal decreases in spring in N and E of North Island
Extreme rainfall
Heavier and/or more frequent extreme rainfalls, especially where mean rainfall increase predicted (M)
No change through to halving of heavy rainfall return period by 2030s; no change through to fourfold reduction in return period by 2080s (L)
Increases in heavy rainfall most likely in areas where mean rainfall is projected to increase
Snow Snow cover decrease, snowline rise, shortened duration of seasonal snow lying (all M)
Unknown Unknown
Glaciers Continuing long-term reduction in ice volume and glacier length (M)
Unknown Reductions delayed for glaciers exposed to increasing westerlies
Climate change and the New Zealand marine environment 5
Wind (average)
Increase in the mean westerly windflow across New Zealand (M)
By 2080s, could be from slight increase up to doubling of mean annual westerly flow (L)
Unknown
Strong winds Increase in severe wind risk possible (L)
Little change up to double the frequency of winds above 30m/s by 2080s (L)
Unknown
Storms More storminess possible, but little information available for New Zealand (L)
Ex-tropical cyclones might be slightly less likely to reach New Zealand but if they do their impact might be greater. Intensity or frequency of mid-latitude storms might increase (L)
Unknown
Sea level Increase (VH) 9-88 cm rise (New Zealand average) between 1990 and 2100 (VH)
Uniform?
Waves Increased frequency of heavy swells in regions exposed to prevailing westerlies (M)
Unknown Increase in frequency of heavy seas and swell along western and southern coasts
Storm surge Storm surge height and extreme storm-tide level may increase (L)
Unknown Unknown
Ocean currents
Various changes plausible, but little research or modelling yet done
Antarctic circumpolar current likely to accelerate, would further isolate waters on Campbell Plateau and increase inflow of cold water to Chatham Rise. Increase upwelling of cooler subsurface waters along coast. (L)
For projected increased westerlies, coasts affected are west coast SI and northeast coast NI, but changes in north-south wind component could substantially modify which regions affected.
Note 1. Changes in the return period of heavy rainfall events may vary between different parts of the country, and will also depend on the rainfall duration being considered.
1.3 Current work to update these scenarios
Currently NIWA is working on an update to the climate change guidance manual for
local government in New Zealand (MfE 2004a,b). The update uses a selection of the
Climate change and the New Zealand marine environment 6
latest GCM projections from the IPCC Fourth Assessment (AR4) report (see Chapter
10, Meehl et al. 2007).
The IPCC made subtle changes between the Third and Fourth Assessments in the way
they expressed the climate projections. The Third Assessment stated: “The globally
averaged surface temperature is projected to increase by 1.4 to 5.8°C over the period
1990 to 2100. These results are for the full range of 35 SRES scenarios, based on a
number of climate models.” In the Fourth Assessment, the projections were expressed
as changes between 1980-1999 and 2080-2099, and projections were given separately
for 6 marker scenarios which spanned the range of the full 35 SRES scenarios. For
each of the 6 scenarios, a best estimate was provided, as well as the likely range. The
full range in global temperature increase over the 6 marker scenarios of the Fourth
Assessment was 1.1 to 6.4°C.
The New Zealand downscaled projections follow the revised IPCC approach. That is,
changes are relative to 1980-1999, which is identified with the “current climate” and
still abbreviated as “1990”. Changes are calculated for the two future periods 2030-
2049 (“2040” for short) and 2080-2099 (“2090”). Thus, the New Zealand projections
are 50 and 100 year changes, between the present (“1990”) and future periods centred
on 2040 and 2090.
2. Sea level rise
New Zealand relative sea level rise (SLR) is predicted to be similar to the global
projections of SLR by the Intergovernmental Panel on Climate Change (IPCC) Third
Assessment Report at around 1.8 mm/year (MfE 2004). This is due to the thermal
expansion of the oceans and freshwater input from ice-melt (Harley et al. 2006).
SLR will not be 'temporary' and is expected to continue for several centuries even if
greenhouse gas emissions are reduced. This is because of the long lag times needed
for the deep oceans to respond to ocean surface heating, and the expected
contributions from the massive Antarctica and Greenland ice sheets after 2100. IPCC
projects that mean sea level will rise between 9 and 88 cm between 1990 and 2100
(McCarthy et al. 2001). These projections do, however, rely on a constant rate of sea-
level rise acceleration of 0.013 ± 0.006 mm yr-1 (Church & White 2006).
In the Pacific localised climatic cycles will also affect the rate of SLR. The
Interdecadal Pacific Oscillation (IPO) which alternates between positive and negative
phases every 20 to 30 years appears to have changed around 1998 or 1999 to a
negative phase. Due to more balance resulting between El Niño and La Niña episodes
Climate change and the New Zealand marine environment 7
this is expected to contribute to an increased rate of SLR than that experienced over
the previous positive phase of IPO from 1976 to 1998. In which case, the next 20 to 30
years should see a faster rise in sea level than the mean long-term trend of 1.7 ± 0.5
mm/yr through the 20th century (Bindoff et al. 2007). This local acceleration of SLR is
irrespective of any changes in the rate of SLR attributable to global warming.
In Australia, much greater sea level rise is projected on the east coast than the west
due to the increased southward penetration of the warm East Australian Current
(EAC), which causes water there to expand more than in other regions (Poloczanaska
et al. 2007). Slightly higher relative increases in SLR could also therefore be seen in
northeastern New Zealand if predicted strengthening of the East Auckland Current
occurs (see Section 5).
2.1 Projected effects
Global warming is projected to raise sea level in the 21st century, with expected
dramatic impacts in low lying areas subjected to coastal hazards including inundation,
subsidence and erosion. Table 2 shows the magnitude of projected change predicted
by the IPCC in 2001 (MfE 2004).
Table 2. Projections of future sea level rise (SLR) for New Zealand above 1990 mean sea level.
Scenario Climate factors SLR by 2050 (m) SLR by 2100 (m)
Recommended NZ SLR magnitudes 0.2 0.5
IPCC-2001 'Most-likely' mid-range [Figure A2.7]
Averages of climate models & socio-economic scenarios 0.14-0.18 0.31-0.49
IPCC-2001 Outer ranges [Figure A2.7]
Intermediate zones Upper & lower extreme zones
0.10-0.24 0.05-0.31
0.21-0.70 0.09-0.88
Average historic NZ trend continues (0.16 m/century)
No change in sea-level trend over the 1900's
0.08 0.16
The effects of this SLR will be increased risk of low-lying areas to inundation by
increased water depths, which in turn will exacerbate damage from flooding events
and discharge from backed up rivers and stormwater systems. Inundation of low-lying
areas and drowning of intertidal habitats will occur more frequently during storm
Climate change and the New Zealand marine environment 8
events, accelerating the effects of coastal erosion. Resulting increased sedimentation
will smother habitats and species not adapted to high sediment loads. However, in
sheltered areas where sediment accumulation is high, the resulting rise in the level of
the shore may keep pace with, or even exceed, the rate of SLR. Other effects will be
changes in tidal variation increasing the mean tidal level and the shape of the tidal
prism, water movement alterations, and increased seawater intrusion into estuaries and
rivers (Short & Neckles 1999).
2.2 Vulnerable habitats and species
2.2.1 Estuaries and wetlands
Estuaries and wetlands are already disappearing worldwide due to a variety of
economic and social activities including filling, reclamation, and sediment
interception (Valiela et al. 2004). Such losses are of concern because these wetlands
provide important functions, including export of energy-rich material to deeper waters
and nursery habitats, shoreline stabilisation, and intercept land-derived nutrients and
contaminants. Although wave heights inside estuaries are often limited due to the
shallow water depths and short fetch lengths, waves can make a significant
contribution to inundation when strong winds combine with extreme water levels.
Ocean waves overtopping narrow sand or gravel barriers can also significantly
increase water levels in lagoons. It has been estimated that world-wide SLR could lead
to the loss of up to 22% of coastal wetlands (McCarthy et al. 2001). SLR will
exacerbate the loss of these habitats due to more frequent inundation and added stress
to compromised keystone species and habitats.
Important components of estuaries and wetlands are seagrass beds, which are known
for providing valuable community functions including food and nursery habitat for
many commercially and recreationally important fish, invertebrate habitat, and food
for waterfowl (Short & Neckles 1999; Turner & Schwarz 2006). Other important
ecosystem functions include regulating dissolved oxygen, chemical and physical
environment, suspended sediments, chlorophyll, and nutrients in the water column.
The effects of SLR on seagrass will be a redistribution of existing habitats, causing
some plants to relocate to areas they can tolerate, and others may be able to expand
their distribution inland. This will result due to salinity changes affecting seed
germination, propagule formation, photosynthesis, growth and biomass. Increased
water movement, tidal currents and wave action will reduce water clarity affecting
photosynthesis. Disease and fouling by epiphytes on seagrass are also expected to
increase (Short & Neckles 1999).
Climate change and the New Zealand marine environment 9
2.2.2 Mangroves
In geological timeframe, SLR has been cited as one of a range of contributing factors
in the loss of mangroves in the Poverty Bay – East Cape region in New Zealand,
which is below its current southern limits of Avicennia (Mildenhall 1994). In some
parts of the world, mangrove forests were able to persist during the Holocene when
sea level rose at rates of 8-10 mm/year due to the mitigating effects of large sediment
inputs (Woodroffe 1990).
Where sediment accumulation does not keep pace, rising sea level may either reduce
the width of the mangrove zone on the shore or cause them to migrate upshore, as
higher levels on the shore become flooded more frequently (McCarthy et al. 2001).
This migration may occur at the expense of saltmarshes behind the mangroves (Harty
2004), unless they too are able to migrate upshore. There is evidence for such upward
migration of mangroves during periods of SLR from studies of shoreline changes of
glacial/interglacial cycles (Wolanski & Chappell 1996). However, there may be much
larger shorter-term variation in sea level (Ramsay 2006), so that even if sedimentation
rates or mangrove migration rates are able to keep pace with the average rate of SLR,
there may be net loss of mangroves or saltmarsh during these periods of more rapid
change.
Migration of both mangroves and saltmarshes will be restricted where coastal
defences are present – a process referred to as “coastal squeeze”. In parts of Europe,
such as the Netherlands and eastern England, this potential loss of coastal habitat has
been addressed through a strategy known as “managed realignment”. Rising sea levels
are allowed to breach existing sea defences and low-lying areas behind them are
flooded and potentially revert to coastal vegetation (Wolters et al. 2005). These areas
are generally uneconomic farmland that was formerly created by infilling of the coast.
The strategy thus allows the preservation of coastal habitat and avoids the high cost of
defending low-value land.
Migration of mangroves to higher latitudes has also been predicted as a result of
climate change (McLeod & Salm 2006) as increasing average temperatures allow
them to survive at higher latitudes. Expansion of the geographical range of mangroves
in New Zealand will depend on whether mangrove propagules can actually reach
suitable habitats further south, and may also be limited by periodic extremes of
temperature.
All of these potential effects are subject to considerable uncertainty and are likely to
be influenced by other coastal changes occurring at the same time (Morrisey et al.
Climate change and the New Zealand marine environment 10
2007). These include changes in coastal geomorphology, water movement and
associated patterns of erosion and sedimentation. These factors make it very difficult
to predict how mangroves will respond to SLR at any given location or over a
particular period of time.
2.2.3 Rocky intertidal habitats
Rocky intertidal zones are one of the most productive environments on earth (Hurd
2000) and offer a dynamic range of habitats subject to environmental challenges of
aquatic and aerial climate regimes. As a result, rocky shore organisms and
assemblages may serve as early warning systems for the impacts of climate change
(Helmuth et al. 2005, 2006; Mieszkowska et al. 2006). Thermal and desiccation stress
can set the upper limits of zonation of many intertidal organisms (Davenport &
Davenport 2005). As position on the shore determines the length of time a sessile
organism is covered by seawater, the higher up the shore the shorter the immersion
time during the largest tides. The tidal ranges vary around the coast, but the range
differs from 1-2 m on the east coast to 3.5-4 m on the west coast (LINZ 2007). Tidal
influence determines the position of organisms on the shore (Raffaelli & Hawkins
1996), but tidal effects are modified by factors such as wave force, humidity, substrate
topography and biotic and behavioural interactions (Underwood & Jernakoff 1981).
Wave action acts as mechanical stress on intertidal organisms, but varies greatly
depending on shore slope, fetch and bathymetry waves have travelled over (Denny
1988). Erosion of rocky shores generally occurs during storms when elevated sea
levels and large waves attack the base of cliffs, resulting in undermining and failure
(MfE 2004a). Cliffs also erode slowly under wetting and drying processes. Increasing
SLR will result in increased erosion of these habitats potentially altering species
composition, alongside the gradual migration of species up-shore. Increased
sedimentation has been shown to affect the settlement and germination of the spores
of habitat-forming intertidal algal species (Schiel et al. 2006). Much like estuarine
habitats, coastal squeeze of species can also occur, but this would be more noticeable
on steeply sloping shores or those bordered by cliffs. In areas where seawalls and hard
protection measures are installed to protect against SLR, species may colonise these
structures if appropriately designed and constructed. Inappropriately designed
protective structures, can lead to displacement of erosion pressures laterally along the
beach.
Climate change and the New Zealand marine environment 11
2.2.4 Shallow subtidal reefs
Shallow reefs are very productive habitats (Taylor 1998) and support a large
proportion of New Zealand’s coastal biodiversity, despite forming a relatively small
percentage of the continental shelf habitat. Rocky reefs also support a large number of
endemic species, and their topographical complexity means that they contain many
habitat types within a small geographical area.
There are likely to be few long-lived sessile organisms unable to alter their vertical
distribution on reefs in the face of projected SLR. Rather, the effects on shallow reef
assemblages are likely to be more subtle and result from indirect effects of SLR,
including increased erosion and wave exposure, subsequent inundation by sediments
and detrital matter (Bishop & Kelaher 2007), and resuspension and transport of
sediments during more frequent severe storm events. Seaweeds may be especially
vulnerable to such impacts. Seaweeds provide very important ecological services
(Schiel 1990, Taylor 1998; Shears & Babcock 2004) such as primary production,
physical habitats, refugia for invertebrates (Taylor & Cole 1994; Anderson et al. 2005)
and fishes (Choat & Ayling 1987; Willis & Anderson 2003), nutrient cycling (Taylor
& Rees 1998, Tyler & McGlathery 2006), and food resources for rocky reef
communities (Zemke-White & Clements 2004; Taylor & Brown 2006). Reduced light
levels, scouring and inundation by sediment at the base of reef systems may become
more common reducing algal depth limits, whereas, storm surges could lower the
upper limits for algal assemblages (Graham 1997). The loss of habitat-forming algae
can cause cascading effects for other species resulting in unforeseen reductions in
some species (Moore et al. 2007). Increased SLR could however offset any impacts
currently present due to increased UV resulting from reduced stratospheric ozone
concentrations. Another subtle effect could result from vertical range squeeze when
abiotic stress shifts the vertical range of one species into the vertical range of a
consumer or competitor (Harley et al. 2006).
The effects of overfishing reducing keystone predator species in reef ecosystems may,
however, overshadow SLR and climate change impacts on important habitat-forming
algal communities as seen in California (Steneck et al. 2002). When the predator
species, such as rockfish, at the top of the food chain are removed, then the species
that they normally eat, such as snails and barnacles, begin to increase in number.
Many of these are herbivores that eat kelp. When herbivore numbers increase, they
decrease the amount of kelp, in turn changing how kelp forests look and the type of
species that are associated with the kelp forest. Thus, managing overfishing of
keystone species may be more important to make reef communities more resilient to
climate change (Folke et al. 2004).
Climate change and the New Zealand marine environment 12
2.2.5 Open coast sand beaches
Coastal sandy beaches, while not supporting particularly diverse communities as
compared with rocky reef systems, play an import role in buffering the land from
wave and wind energy. Increased SLR will be most hazardous to areas of the coastline
bordered only by foreshore beaches and sand dunes, where run-up of waves can reach
more than 6 m above MSL leading to blow-outs of dunes and flooding low-lying areas
behind the dunes (MfE 2004a). The subsequent erosion and increased sediment
transport will impact on bordering reef systems, and soft-sediment communities
below. In situations where beaches are bounded by hard artificial structures, protection
from coastal inundation is dependent on the height, slope and type of structure. In
general, the lack of dissipation of energy from these structures results in higher wave
run-up than would occur on natural beach materials. This will be exacerbated by the
increased storminess expected with climate change.
3. Wind and rainfall patterns
Climate models predict that for mid-range temperature change projections, the mean
westerly wind component across New Zealand will increase by approximately 10% in
the next 50 years (Mullan et al. 2001b, MfE 2004a) with scenarios leaning strongly
towards increasing westerly flow, particularly in the annual mean. The mid-range
projection for the 2080s is a 60% increase in the annual mean westerly component of
the flow. Projected changes in the north-south wind component are less clear. Strong1
winds are associated with intense convection (expected to increase in a warmer
climate) and with intense low-pressure systems that might also become more common.
Thus, an increase in severe wind risk could occur, which has been identified relating
to the increasing number of intense cyclones in the North Atlantic (Knippertz et al.
2000). For mid-range temperature change scenarios, the highest wind speed expected
to occur once per year could increase by about 3% by 2080. Over the sea or flat land
the annual frequency of occurrence of winds of 30 m/s or above might increase by
about 40% by 2030 and 100% by 2080 (MfE 2004a). There is however considerable
uncertainty in these predictions. How extreme winds affect different parts of New
Zealand is also likely to change in the future. The regional distribution of wind
extremes is probably dependent on the stability of the air approaching the land from
the ocean, which may change.
1 A "strong" wind is in the range 22-27 knots, or 11-14 m/sec
Climate change and the New Zealand marine environment 13
Figure 2. Highest expected annual precipitation change in New Zealand between 1971-2000 and 2071-2100.
A warmer atmosphere can hold more moisture (about 8% more for every 1°C increase
in temperature), so more intense rainfall events are "very likely over many areas"
(McCarthy et al. 2001). Despite a lot of variability among models in the 2080s annual
mean rainfall, the regions of Taranaki, Manawatu-Wanganui, West Coast, Otago and
Southland tend to show increased rainfall for all scenarios (Figure 2), compared to
Climate change and the New Zealand marine environment 14
Hawkes Bay and Gisborne which show rainfall decreases for all scenarios. Seasonally,
the largest decreases occur in the north and east of the North Island in spring (MfE
2004).
For a modelled 2°C change in temperature during a storm over New Zealand
mountains a 6-7% increase in both maximum and catchment averaged rainfall was
predicted (Gray and Larsen 2003). Similar increases were predicted for a 10% increase
in wind speed. Increasing both wind speed and temperature together led to a 16%
increase in rainfall. Various modelling studies suggest that heavy rainfall events will
occur more frequently in New Zealand over the coming century, but the likely size of
this change is uncertain. Of importance to South Island rivers, snow cover will
decrease and snowlines rise as the climate warms, but as warmer air holds more
moisture more winter snow is expected at high elevations, so warming does not rule
out increased winter snowfall and spring discharges to the sea.
3.1 Projected effects
Predicted increased intensity of storms will manifest as increased intensity winds and
rainfall events. These will impact the coastline by increasing erosion due to higher
intensity wave forces eroding the coastline, and increased erosion of terrestrial
catchments respectively. These will exacerbate drainage and flooding risks, increasing
the volume of sediment discharged to the coast, and increase the resuspension of soft
sediments in shallow environments. The resulting increased turbidity will further
decrease light levels. Increased rainfall intensity will also depress salinity levels in
estuaries affecting stratification, sediment transport and deposition rates.
3.2 Vulnerable habitats and species
3.2.1 Estuaries and soft sediment communities
A 7 mm inundation of terrestrial sediment has been shown experimentally to reduce
soft sediment macrofaunal individuals and species by 50% (Lohrer et al. 2004). A
thicker deposit of 2 cm thick can cause underlying sediments to become anaerobic,
killing all infauna, with incomplete recovery seen after 603 days (Thrush et al. 2003,
Thrush et al. 2004). Heavy inundations of sediment can completely bury infaunal and
epifaunal bivalves (McKnight 1969) unless waves and currents can disperse sediment
plumes. Such catastrophic events severely compromise subtidal habitats. More
importantly, are the frequent and widespread sublethal impacts of terrestrial sediment
contamination which cause chronic physiological stress to plants and animals leading
to degenerative change (Thrush et al. 2004, Poloczanska et al. 2007). Following
Climate change and the New Zealand marine environment 15
catastrophic events the loss of suspension feeding bivalves can uncouple the seafloor
and water column processes, allowing for regime shifts towards primary production
dominated by phytoplankton (Dame 1993, Kemp et al. 2005). This is exacerbated by
reduced light levels reducing benthic primary production because seaweeds and
seagrasses typically require more light for photosynthesis than phytoplankton (Duarte
1991, Markager & Sand-Jensen 1992).
3.2.2 Mangroves
As with SLR above, mangroves are predicted to expand in range in areas where
increases in temperature allow for their colonisation to higher latitudes, and with this
expansion will be increased conflict over the aesthetic values of mangroves and the
pressures from coastal urban developments (Morrisey et al. 2007). Because mangroves
are habitat modifiers that trap sediment, they may mitigate SLR in parts of the country
exposed to increased sedimentation from climate change induced rainfall increases
such as the west coast of the North Island. However, if mangroves were to spread
further south to historic southern limits in Poverty Bay (Mildenhall 1994), they may
be less able to cope with SLR there due to predicted drier conditions reducing
sediment inputs, which could hinder their spread during periods of drought. With SLR
and increased rainfall, mangroves are expected to outcompete salt marsh plants
leading to the loss of salt-marsh habitats (Poloczanska et al. 2007). Hydrodynamic
modifications resulting from urban and rural irrigation and drainage are however
likely to be overriding factors in the expansion of mangroves (Poloczanska et al.
2007).
3.2.3 Subtidal rocky reefs
Laboratory and in situ experiments on a gradient of sediment contamination between
Whitianga Harbour mouth and Hahei demonstrated both direct and indirect impacts of
terrestrial sediment on biodiversity of rocky reefs (Schwarz et al. 2006). Indirect
effects were decreased photosynthetic potential of Ecklonia radiata, with the greatest
degree of acclimation to low light levels at the high sediment sites. This suggested
reduced production of all primary producers. Of greatest concern was the large
decrease in epifuanal biomass colonising E. radiata, since epifauna are estimated to be
responsible for about 80% of flow of energy and materials through rocky reef
communities (Taylor 1998). The direct effects of sedimentation were sublethal
impacts on filter feeders with evidence of increased energy requirements compounded
by synergistic effects with duration of exposure. Mean survival of the amphipod Aora
typica decreased logarithmically in increasing suspended sediment concentrations, and
paua and kina larval bioassays showed lethal effects at high concentrations and again
Climate change and the New Zealand marine environment 16
synergistic effects with duration of exposure. In addition, Walker (2007) has shown
that fine sediments can inhibit the settlement of kina larvae, and reduce the survival
rate of recruits. Disturbingly, thresholds of “minimum concentration of effect”
recommended by Schwarz et al. (2006) for chronic and toxic impacts of sediment
contamination fell well below levels that some rocky reef environments experience at
both Whitianga and Hutt River.
3.2.4 Intertidal coastlines, animals and seabirds
While natural disturbances like storms may be important for maintaining diversity in
coastal ecosystems, increased frequency and severity of storms may reduce their
resilience by detaching coastal plants and animals, further destabilising coastlines
(Poloczanska et al. 2007). While ex-tropical cyclones might be slightly less likely to
reach New Zealand later this century, their impact may be greater (MfE 2004a).
Cyclones are considered a major threat for breeding colonies of some seabirds in
northern Australia (King et al. 1992; Garnett & Crowley 2000) and also account for
turtle kills and destruction of breeding and feeding habitats (Limpus & Reed 1985).
Storms also account for Antarctic fur seal deaths and mother-pup separations in the
Shetland Islands (Boveng et al. 1998), thus, an increase in storm severity or return
times could affect New Zealand fur seal populations especially on the west coast of
the South Island where wind and storms are predicted to increase.
In wave surge zones on exposed rocky shores, changing wave climate and resulting
hydrodynamics will affect the resilience of alga to stay attached. Algae larger than
around a tenth of a millimetre extend beyond the protection of the viscous boundary
layer (Denny 1988) and have to adapt to surviving the energy forces generated by
larger waves (Stevens et al. 2004). For survival and propagation, large seaweeds like
Durvillaea antarctica reduce the loading by around 30% due to frond interactions
between neighbouring individuals (Stevens et al. 2004). Therefore, if localised
catastrophic loss occurs, recovery may be difficult under a global warming scenario at
exposed sites. However, determining the role of climate change will be difficult as
recruitment of D. antarctica has been shown to be influenced by grazing by butterfish
Odax pullus in the absence of cover by adult kelp (Taylor & Schiel 2005). ENSO
climate variations have also been shown to affect kelp populations in southern
California with reduced density during extended periods of above normal sea surface
temperatures and increased precipitation associated with El Niño events (Grove et al.
2002).
Climate change and the New Zealand marine environment 17
4. Ocean acidification
4.1 Projected effects
A recent review of ocean acidification by the UK Royal Society has stimulated
significant concern and considerable international research activity into ecosystem and
biogeochemical impacts of decreasing pH in the surface ocean (Royal Society 2005).
The uptake of anthropogenic CO2 from the atmosphere has already resulted in a pH
decrease of 0.1 pH units since 1750 (Trenberth et al. 2007) with a further decrease in
surface ocean pH of 0.4 pH units predicted by 2100 (Caldeira & Wickett 2003; Feely
et al. 2004). This is outside the range of natural variability and will impact biological
processes such as ocean productivity, food web structure and carbon sequestration.
Recent work (Le Quére et al. 2007) has suggested that strengthening westerly winds
over the Southern Ocean (expected under IPCC scenarios) has reduced the capacity of
the ocean to act as a CO2 sink (Sabine et al. 2004). This occurs by outgassing of CO2
back into the atmosphere by wind-driven upwelling. This phenomenon may reduce the
previously projected rates of acidification, but the Southern Ocean is still a significant
sink for CO2 (Ho et al. 2006).
The only NZ study that collects relevant information is the bimonthly Munida Time
Series collected along a transect off the Otago shelf, which has not identified any
significant change in pH in Sub-Antarctic Water over the 8-year survey period (K.
Currie, unpubl. data), despite a steady increase in atmospheric CO2 during this period.
It should be noted that the expected decrease in pH induced by increases in
atmospheric CO2 is small relative to the intra-annual variability and that a trend in
acidification may become evident a the time-series is extended. Time-series
measurements of longer duration in the Atlantic and Southern Ocean have identified
increasing acidification of surface waters consistent with increasing atmospheric CO2
(Santana-Casiano et al. 2007; Yoshikawa-Inoue & Ishii 2005).
Some experiments are currently being undertaken in NZ examining pH sensitivity of
coralline algae (C. Hurd, University of Otago), but there are no studies currently
underway to determine whether NZ EEZ or Southern Ocean ecosystems will adapt or
collapse in response to acidification.
Organisms that have a carbonate exoskeleton will be most susceptible as acidification
will reduce the saturation state, and so availability, of calcium carbonate. Most
vulnerable will be groups such as pteropods (zooplankton that are a dominant
component of the pelagic food web, particularly in the Southern Ocean),
coccolithophores, cold water corals, benthic littoral and sub-littoral molluscs,
Climate change and the New Zealand marine environment 18
echinoderms and crustaceans (Orr et al. 2005; Langer et al. 2006). Current evidence
suggests that the pteropods, zooplankton with a calcareous shell that are a dominant
component of the Ross Sea pelagic food web, are most susceptible with shell
dissolution occurring within 48 hours when incubated at 2100 CO2 levels in laboratory
experiments (Orr et al. 2005). The pteropods are an integral part of the Southern
Ocean foodweb and replace krill as the dominant zooplankton in the Ross Sea, but it is
currently unknown whether acidification will shift their geographical range to the
north or whether they will be replaced in the food chain.
In addition, there will be impacts on non-calcifying organisms, including autotrophic
bacteria, cyanobacteria and higher organisms such as fish and squid.
4.2 Vulnerable habitats and species
Calcifying organisms in the ocean use two polymorphs of CaCO3, calcite and
aragonite, which differ in their physico-chemical properties. Aragonite is more
sensitive in terms of pH-dependence, and availability is temperature-dependent with
aragonite saturation being reduced most in colder waters. This suggests that ecosystem
response to acidification may become apparent first in Southern Ocean and sub-
Antarctic waters, as supported by recent observations that polar waters will be
undersaturated with aragonite within 50 years (Orr et al, 2005) (Figure 3).
Consequently organisms that use this form, including corals, pteropods, and some
calcareous algae, are likely to respond to lowering pH before other groups (Table 3).
This does not mean that taxa that depend primarily on calcite are not at risk. Some
groups use a Manesium-Calcite combination that is potentially more susceptible to
lower pH than aragonite.
Increasing acidity is likely to put all calcifying taxa under physiological stress, with
possible consequences for growth and productivity across the board, especially in high
latitudes where calcium concentrations are already naturally low. Indeed, recent
research has found that long term reconstructions of past climate variability are
possible using δ18O-time series in crustose coralline red algae (Halfar et al. 2007).
Thus, despite the increased resistance to acidification of calcite forms, they will
eventually become vulnerable. This has implications for the stability of ecosystems
including calcareous species that are major predators and/or grazers. For example sea
urchins (Evechinus chloroticus) are known to be important grazers of macroalgae on
northern New Zealand reefs (Andrew & Choat 1982), and spiny lobsters important
predators of urchins (Babcock et al. 1999; Shears & Babcock 2002).
Climate change and the New Zealand marine environment 19
Figure 3. Distributions of (A) aragonite and (B) calcite saturation depths in the global oceans. The level at which aragonite and calcite are in thermodynamic equilibrium is known as the saturation depth. This depth is significantly shallower for aragonite than calcite, because aragonite is more soluble in seawater than calcite (from Feely et al. 2004. Science 305: 362-366. Reprinted with permission from AAAS).
Increasing CO2 levels have the potential to reduce productivity of all marine fauna by
increasing the energetic demands of respiration. Although large increases in CO2
concentration are likely to have only minor direct effects on oceanic productivity from
phytoplankton (Beardall & Raven 2004, Giordano et al. 2005), CO2 and acidity
covary, making it difficult to separate the effects of increasing CO2 concentration and
decreasing pH. Where primary productivity is dependent on calcareous organisms
(such as coccolithophores), acidification could result in the collapse of whole food
webs, at least at local scales. Coccolithophores, however, are not major contributors to
southern ocean productivity (F.H. Chang, pers. comm.), and projected changes in pH
are unlikely to have major effects on primary production in the short- to medium-term.
They are however a potentially significant source of the trace gas, dimethylsulphide
(DMS) which influences aerosol production in the marine troposphere and
subsequently the albedo (reflectance) of the atmosphere.
Climate change and the New Zealand marine environment 20
Table 3. Comparison of the characteristics of the aragonite and calcite forms of CaCO3.
Aragonite Calcite
Structure Orthorhombic triagonal
Solubility High Low
Calcifying species Corals, pteropods, macroalgae Foraminifera, macroalgae, coccolithophores, Crustacea
No significant evidence yet exists of acidification effects on coastal ecosystems
(Nicholls et al. 2007). Some experimental evidence indicates that increasing CO2
levels may have indirect, but variable, effects on kelp growth and may delay decay
processes resulting in reductions in shallow-water nutrient recycling (Swanson et al.
2007), which can have consequences for productivity. Projections indicate that
aragonite saturation levels will decrease considerably by 2100 (Figure 4), and calcite
will probably follow suit. Although New Zealand waters contain photosynthetic corals
– already known to be extremely vulnerable (Royal Society 2005; Poloczanksa et al.
2007) – only at the Kermadec Islands (Schiel et al. 1986), reefs from shallow coastal
habitats to deepwater seamounts possess corals that form important habitats
throughout the region (Cairns 1995). Indeed the unique shallow cold-water coral
ecosystems in Fiordland are particularly exposed and so vulnerable to acidification2. It
has been recently mooted that changing aragonite saturation levels are likely to place
70% of the world’s known deep-sea bioherm-forming corals in unsaturated waters by
2100, making these habitats increasingly marginal for coral survival (Guinotte et al.
2006; Turley et al. in press).
Acidification may become a threat to the profitability of the New Zealand aquaculture
industry and some fisheries if it causes cooler, more southern coastal waters to become
calcium-deficient. Crustacean and mollusc species may allocate relatively more
energy to maintaining chemical balances at the expense of growth and reproduction.
Crustaceans may spend longer periods unable to feed after moulting, and remain
vulnerable to predation for longer. Some molluscs may experience a reduction in shell
strength. For example, abalone shell is formed from layers of aragonite along with
calcite and proteins (Belcher et al. 1996) and may be vulnerable. Bivalves are
particularly susceptible at the juvenile stages when their surface area: volume ratio is
higher. Although New Zealand’s main aquaculture species, Perna canaliculus,
possesses a strong periostracum making it less vulnerable to calcium loss, continuing
2 Note this does not include the iconic black coral Antipathella fiordensis, as this species is not calcified.
Climate change and the New Zealand marine environment 21
acidification could conceivably result in a more brittle shell, reducing market value
and increasing handling costs. Experimental work is needed to determine the likely
risk to cultured species. It should be noted that coastal regions experience greater
variation in pH than open-ocean regions, and so organisms in the latter region may be
more susceptible to ocean acidification. Estuarine systems in particular often have
high CO2, and so it is likely that the extant calcifying species are adapted to this.
Figure 4. Historical and projected changes in the saturation levels of the aragonite form of calcium in world oceans (from Feely et al. in press, with permission, available through http://iodeweb3.vliz.be/oanet/FAQacidity.html).
There will also be other impacts on non-calcifying organisms via biogeochemical
changes in nutrient and carbon supply and availability. In warmer sub-tropical water
recent evidence (Hutchins et al. 2007) indicates that elevated CO2 increases cell
growth and nitrogen fixation by Trichodesmium, a large colonial cyanobacterium.
Cyanobacteria have relatively inefficient carbon-concentrating mechanisms and are to
some extent carbon-limited in the present day ocean; consequently increasing
Climate change and the New Zealand marine environment 22
dissolved CO2 increases cellular uptake via diffusion, so allowing diversion of energy
to growth and nitrogen fixation. Trichodesmium sp. may not be the only potential
“winner”, as nitrogen fixing cyanobacteria are responsible for significant new nitrogen
supply and support community primary productivity and carbon export in nutrient
poor sub-tropical waters. Consequently the positive response to acidification may be
reflected in increased productivity of sub-tropical waters, although there is also the
possibility that this may be limited by the ecosystem being driven into phosphate
limitation.
Impacts on the upper food chain may be more direct as well and not limited to indirect
effects such as loss of prey species. Physiological responses such as hypercapnia, the
acidification of the blood, is a potential problem for fish in high CO2 water where the
elevated CO2 gradient between the blood and water in the gills results in increased
acidosis of the blood and decreased oxygen-carrying capacity. Deep-sea fish and squid
are particularly sensitive to increases in seawater CO2 (Ishimatsu et al. 2004); there is
a pH effect on oxygen binding by the main blood pigment, haemocyanin, in squid that
effectively ceases to hold oxygen at a pH of 7.2.
Potential adaptation to acidification is a major uncertainty. Recent research on
coccolithophores suggests that some species, at least over relatively long time periods
(104-105 years), have the capacity for adaptation whereas others do not (Langer et al.
2006). Timeframe is a source of uncertainty in the interpretation of short-term
acidification experiments. Laboratory cultures of the freshwater algae,
Chlamydomonas did not display any adaptation to decreased pH over 1000
generations (Collins & Bell 2004). Conversely morphological adaptation has been
identified in scleractinian corals maintained in low pH water, with calcium carbonate
skeleton dissolution and dissociation of the colonial form accompanying successful
growth of the organism in the naked hydroid form (Fine & Tchernov 2007). It should
be noted that the rate of change in atmospheric CO2 and decreasing pH in the ocean is
more rapid than at any time in the last 800,000 years and likely longer, which may
limit the capacity for adaptation.
It should also be noted that the response to and impact of acidification will be
influenced by synergistic interaction with other climate change variables. This may be
at the physiological level where increased energy diversion to the process of
calcification reduces organism capacity to cope with other environmental pressures
such as increased temperature. Some susceptible groups are not mobile and will have
difficulty adapting their geographical zone; whereas other groups, such as corals, may
be caught in a “crunch’ zone whereby migration to waters of higher calcium carbonate
saturation may be limited by their temperature range.
Climate change and the New Zealand marine environment 23
5. Current patterns and ocean warming
The coupled atmosphere-ocean global climate models do not include enough detail to
show the narrow ocean currents that flow around New Zealand, and very little analysis
has been done of future patterns. This means that no quantitative statements about
these climatic features can be made at this stage.
The upper 700 m of the global oceans on average have warmed about 0.6°C since
1950 (Bindoff et al. 2007). This warming was not uniform spatially. Two thirds of the
increased heat content of the oceans has gone into the upper 700m. In addition, there
are significant horizontal variations, with the New Zealand region showing
particularly strong warming through the 1990s.
There have also been significant global salinity changes, with the general pattern
being freshening at high latitudes and increasing salinity in the tropics and subtropics,
consistent with an acceleration of the hydrological cycle (Wong et al. 1999; Curry et
al. 2003). This pattern means the surface ocean north of New Zealand region is
increasing in salinity, while the surface ocean south of New Zealand is freshening.
The changes in upper ocean temperature and salinity have impacts on stratification,
with warming and freshening serving to increase stratification. Increased stratification
could be expected to decrease nutrient fluxes from the deeper ocean into the euphotic
zone. However, this relationship may not be simple, with complicated feedbacks in the
coupled ocean/atmosphere system.
There are also both observed and predicted changes in deeper water masses, e.g. a
freshening of intermediate water masses. These deeper changes are not discussed here
because, while they are important for climate issues, they are incidental to ecosystem
changes.
There are predictions from global models of what changes are likely in the regional
and global wind patterns. Changes in winds hold clues as to what might be expected in
the ocean (Mullan et al. 2001b). The warm currents flowing down the eastern coast of
the North Island are part of the subtropical gyre (Stanton et al. 1997) and are driven
primarily by the ‘twisting’ action of the winds over the subtropical South Pacific. The
wind patterns over the subtropics show little change in the model runs; however,
westerly winds are projected to increase at higher latitudes and are likely to have
impacts on the current systems. Recent research (Roemmich et al. 2007) has linked the
~1°C warming around New Zealand through the 1990s to a ~20% spin-up of the
subtropical gyre resulting from an enhanced Southern Annular Mode (SAM), i.e.,
Climate change and the New Zealand marine environment 24
increased westerlies south of New Zealand. The predicted future increased high-
latitude westerlies could therefore be expected to result in a spin-up of the subtropical
gyre with stronger current flows and warmer conditions in the gyre centre (i.e., around
NZ).
Figure 5. Major ocean current systems of the New Zealand region
The cold Antarctic Circumpolar Current (ACC) would also be expected to accelerate
as a result of the strengthened high-latitude westerlies. This current system presently
reaches as far north as the southern flank of Campbell Plateau (Figure 5) where it
forms the Subantarctic Front. There are no predictions as to the detailed structure
south of New Zealand, but it is quite likely that the strength of the SAF may change.
Much of the complexity of the current systems is controlled by bottom topography
(Tilburg et al. 2001), reducing the likelihood of large changes in position of major
Climate change and the New Zealand marine environment 25
features, although analysis of recent trends suggests that the core of the SAF flow may
move south and accelerate (Gille 2007).
The predicted increased high-latitude westerly winds also have other implications.
Higher winds will result in more mechanical stirring in the mixed layer and will
increase the likely wave and swell field. There is also the likelihood of increased
localised coastal upwelling.
5.1 Projected effects
Increasing water temperatures should cause a general pole-ward movement in the
distribution of many species, a phenomenon that will be most strongly felt in depths
where water temperatures are most prone to short-term fluctuations (e.g. Helmuth et
al. 2006). Most marine species are adapted to a particular temperature range, and
physiological stress generally occurs when these limits are approached (e.g. Pörtner &
Knust 2007). Metabolic rate is also affected by increasing temperature, and tends to
shorten the duration of the planktonic larval stage of marine organisms. This implies
that a general increase in SST is likely to influence the dispersal of larvae, and may
reduce gene flow between populations (O’Connor et al. 2007).
The observation that warming has been most strongly seen in the upper 700 m of the
water column indicates that coastal and shelf habitats are those most likely to be
vulnerable (Harley et al. 2006). Elsewhere, significant changes in species distributions
have already been documented, particularly in the North Sea (Southward et al. 1995;
Perry et al. 2005), Mediterranean (Sabatés et al. 2006), and North America
(Roemmich & McGowan 1995; Smith et al. 2006). A strengthening series of
southward-flowing currents down the east of the North Island is likely to distribute
warm-temperate species toward Cook Strait and the northern South Island. East Cape
is regarded as something of a biogeographic break point, dividing the warmer Bay of
Plenty from cooler East Coast faunas (e.g. Adams 1994; Roberts & Stewart 2006).
This demarcation is likely to move south or disappear altogether. The process will
have the concomitant effect of reducing or eliminating cooler water species from east
Northland.
Shifts in species composition in assemblages may not necessarily be the direct result
of increasing temperatures, but may occur by cascading responses to changes in
abundance of habitat forming taxa (Schiel et al. 2004). Species that occur in temperate
zones are subject to much greater natural variability in temperature than those
occurring in tropical or polar regions, and therefore tend to have a much wider
tolerance range to temperature per se (Compton et al. in press).
Climate change and the New Zealand marine environment 26
The combination of spin-up of the subtropical gyre together with a warming ocean is
likely to see more tropical pelagic species in New Zealand waters. There were media
reports that sea turtles were seen off Northland in 1998, and marlin were caught as far
south as New Plymouth and Wairarapa. Our knowledge of the current systems of
northeastern New Zealand and the biological effects of their variability, coupled with
observations from previous ENSO events, allows us some ability to predict likely
effects on reef fishes.
The reef fish fauna of east Northland is known to be strongly influenced by the East
Auckland Current (EAUC), which is formed as an offshoot of the East Australian
Current that traverses the Tasman Sea (Stanton et al. 1997). In years when the EAUC
is strong, it facilitates recruitment of subtropical species (probably originating from
coastal Australia, the southern Great Barrier Reef and Norfolk Island) on the
Northland coast and shelf (Francis & Evans 1993). Studies at the Poor Knights Islands
have shown that variability between years is high, and this variability is reflected in
the fish fauna because most subtropical fish recruits do not persist when SST drops
(Choat et al. 1988; Denny et al. 2003). Responses in certain species, particularly
wrasses (Labridae) are rapid. A SST increase of c. 1˚C seen in the Tasman Sea during
1998-2000 (Sutton et al. 2005) followed a switch in ENSO from El Niño to La Niña
and was felt as a 0.5-1.7˚C increase over the long term average SST in the Hauraki
Gulf from late 1998 until mid-2000 (Leigh Marine Lab Climate Records). Fish
surveys in May 1999 detected strong recruitment pulses of Coris sandageri, Coris
picta, Pseudolabrus luculentus and Suezichthys aylingi at the Poor Knights (Denny et
al. 2003). Two of these (C. sandageri and P. luculentus) persisted at only slightly
reduced densities for 2 further years, whereas C. picta and S. aylingi decreased
continuously in density once the La Niña phase of ENSO pattern ended and SST
returned to average values. The latter species therefore probably have less tolerance of
lower temperature than the former. Juveniles of the tropical wrasse Thalassoma
lutescens were also commonly seen during early 1999 (T.J. Willis, pers. obs.), but not
detected subsequently. These observations suggest that rises in mean SST of more
than about 1˚C will establish subtropical species for which Northland is currently
marginal habitat, and result in increasing incidences of truly tropical fishes. The
likelihood of a species becoming established is probably less dependent on changes in
the annual average temperature than changes in winter minima.
Incursions of the EAUC on to the continental shelf at points south of the Mokohinau
Islands have been linked to the strength of episodic periods of easterly winds
(Sharples 1997). Since climate models predict an increase in westerly wind flow,
transport of warmer EAUC water into coastal ecosystems may be reduced, although
the EAUC will remain strong offshore. Limited evidence suggests that increases in the
Climate change and the New Zealand marine environment 27
mean SST in northern New Zealand are likely to reduce the ranges of species with
cold-water affinities. For example, fish monitoring at Hahei, eastern Coromandel
Peninsula, showed density reductions in blue cod (Parapercis colias) during the La
Niña conditions of 1998-99 (Willis et al. 2003). This result is correlative, however,
and research is needed on temperature tolerances of this species to make links between
water temperature and coastal fish density.
The effects of the potential changes in current flow on local-scale eddy and upwelling
systems is unknown over large scales, however changes in the position and
distribution of these is likely to alter patterns of recruitment. Chiswell & Booth (1999)
found distributions of rock lobster Jasus edwardsii larvae to be contained by the
Wairarapa Eddy off the eastern North Island, and suggested that this containment is
necessary to maintain the population. A shift in position or breakdown of the eddy
may have negative consequences for future lobster recruitment. Local-scale upwelling
systems of northeastern New Zealand are seasonal and appear to be driven to a large
extent by interactions between the strength of the EAUC and wind climate (Zeldis et
al. 2004). These upwellings are rich in nitrate that is limiting for the growth and
composition of the phytoplankton assemblage (Chang et al. 2003b; Zeldis 2004).
General increases in SST are likely to alter the reproductive cycles of many marine
species, resulting in earlier spawning times. Centres of productivity (e.g. upwelling
systems) may be influenced by temperature changes where these exceed the normal
tolerance range of primary producers.
Increasing SST over the last few decades has been implicated in an increase in the
reported incidence of disease in marine environments (Harvell et al. 1999, 2002; Ward
& Lafferty 2004). Mass mortality events caused by disease, or interactions between
disease agents and other factors, can cause large-scale changes in assemblage
structure, particularly where they affect habitat-forming species. Natural disease
outbreaks in New Zealand marine species are not well documented, although the
information base is improving through study of pathogens and parasites associated
with the aquaculture industry. Recent natural mortality events have affected pilchards
Sardinops neopilchardus (and S. sagax in Australia), and kelp Ecklonia radiata (Cole
& Babcock 1996) in northeastern New Zealand. Pilchard die-offs were attributed to a
herpes virus (Whittington et al. 1997) and climatic influences were eliminated as a
direct cause (Griffin et al. 1997). Viruses were also implicated in kelp die-offs (Easton
et al. 1997), but other factors, including light limitation from algal blooms and grazing
by epifaunal amphipods (Haggitt & Babcock 2003), were not eliminated as possible
explanations (Cole & Syms 1999).
Climate change and the New Zealand marine environment 28
5.2 Vulnerable habitats and species
Changes in currents and SST are likely to bring about changes that may be felt
throughout entire marine ecosystems, from primary productivity through to apex
predators like sharks, marine mammals (Trites et al. 2007; Simmonds & Issac 2007),
and seabirds (Frederiksen et al. 2006). All elements of the system may therefore be
regarded as vulnerable to change, although in some cases a warming scenario will
have beneficial effects.
It is generally accepted that there are links between ocean climate and the productivity
of many fisheries (Roessig et al. 2004; Ottersen et al. 2006; Brunel & Boucher 2007)
although the exact mechanisms for these links are not always clear. Francis (1993)
discovered a positive correlation between SST and the year class strength of snapper
Pagrus auratus in northern New Zealand, which further investigation has attributed to
larval competence in a superior feeding environment (Zeldis et al. 2005), whereas
Beentjes & Renwick (2001) have correlated recruitment of red cod (Pseudophycis
bachus) with cooler water temperatures.
There has been some research on the possible impacts of warming through the 1990s
on the New Zealand hoki (Macruronus novaezelandiae) fishery (Francis et al. 2006).
This research showed no definitive link between the ocean warming and the declining
hoki stocks, but did illustrate one of the main difficulties in this type of analysis: a
lack of intermediate connecting data between the physical conditions and the fish (e.g.
nutrient data, data about intermediate steps in the food chain). This point was
reinforced by Willis et al. (2007) whose analysis of southern blue whiting
(Micromesistius australis) recruitment on the Campbell Plateau found no link with
SST, but predicted that “good” recruitment years should be expected where sea
conditions were rough in winter, followed by a relatively calm spring. Similarly, and
ten years earlier, Renwick et al. (1998) had found correlations between the
survivorship of pre-recruit southern gemfish (Rexea solandri) and SST along with
increases in south-westerly winds. As with subsequent studies, causal mechanisms
could only be inferred. Potential solutions are to either continue to increase the time
series of data available for analysis, or seek to obtain data at spatial scales likely to
reflect biological influences on recruitment and survivorship. Useful (but currently
unavailable) information might include detailed data on mixing or stratification of the
water column, distributions and relative availability of major prey species through
early development, or the ways in which conditions affect the distribution of
predators.
Climate change and the New Zealand marine environment 29
6. Indirect effects
6.1 Primary production
The production of organic matter by marine phytoplankton is the driving force behind
ocean ecosystems in New Zealand as throughout the world. The process is termed
“Net Primary Production” (NPP), and measured as milligrams of organic carbon
produced by photosynthesis per square metre per day (mgC/m2/d). Net Primary
Production can be measured accurately from ships, but they cannot adequately map
NPP over areas the size of the New Zealand EEZ. Over the last decade, methods have
been developed to estimate NPP using satellite observations of the ocean which
observe the whole world every 2 days. More than ten different approaches have been
tried and there are significant differences in their results. None of the methods has
been adequately validated in New Zealand waters but work to date suggests that the
model based on Behrenfeld & Falkowski (1997) best fits the measurements made at
sea.
6.1.1 Carrying capacity
Average NPP places an upper limit on the carrying capacity of marine ecosystems: the
amount of production by predators such as fish, shellfish, marine mammals, and
seabirds that can be sustained in the long term. There is significant complexity in the
relationship between NPP and predator abundance. Organic matter produced by
phytoplankton is not directly consumed by these higher predators. Instead, a range of
organisms, including zooplankton, link phytoplankton to higher predators through the
ocean food-web. These linking organisms have varied life histories which affect the
number and type of predators that can be supported by a given amount of NPP.
Nevertheless, large scale changes in NPP due to oceanographic regime shifts would
significantly affect New Zealand’s marine ecosystems and fisheries, so that
monitoring NPP is an important component in ecosystem-aware fisheries
management.
6.1.2 Primary production around New Zealand
Net primary production is high close to the New Zealand shore (within 80 km in
Figure 6). Results using satellite methods can be inaccurate near land so these
production rates should be treated with caution. In the open ocean, NPP is highest to
the east of New Zealand in the Subtropical Front where subantarctic and subtropical
waters mix together. There is a clear seasonal cycle in NPP for the New Zealand
region (Figure 7). Highest production rates occur in spring when warming stabilises
Climate change and the New Zealand marine environment 30
the surface layer of the ocean. Long-term changes in average PP over the New
Zealand region are small and variable. There is a suggestion of a 1% per year decrease
on average, with a realignment occurring in mid-2002.
Figure 6. Primary Production (PP) for the New Zealand region estimated from the Vertically Generalized Production Model of Behrenfeld & Falkowski (1997) and based on MODIS satellite ocean colour data. Data shown are the log-average values for July 2002 – October 2006.
6.1.3 Global primary production
On a global scale, high NPP and high fisheries yields go together (see Figure 8). The
central oceans are comparative deserts. Most of the world’s fisheries yield comes from
ocean less than 500 km from land. Conspicuous areas of high NPP (and high fisheries
yields) include the Benguela upwelling system off the west coast of South Africa, the
Chilean upwelling system, European shelf seas, and the Canary upwelling system off
West Africa. Australasian waters generally have low productivity – there are no
extensive shallow continental shelves or upwelling systems, the two features
responsible for the highest productivities around the world. New Zealand sits astride
the Subtropical Front which boosts primary production in the New Zealand region.
Climate change and the New Zealand marine environment 31
100
200
300
400
500
600
700
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Date
NP
P (
mgC
m-2
d-1
)
-20
-10
0
10
1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007
Date
Res
idu
al (
%)
Figure 7. Top: Average Net Primary Production (NPP) over the New Zealand region estimated from the Vertically Generalized Production Model of Behrenfeld & Falkowski (1997) and based on two sets of satellite ocean colour data (MODIS: red, and SeaWiFS: blue). Bottom: Change from the average monthly condition.
Sixty-two “Large Marine Ecosystems” have been recognised by a number of
international organisations (Figure 8). NPP in the New Zealand region, as estimated
from satellite data, is just above the global average for these ecosystems, at 24th out of
62. Globally, there are about the same number of increasing trends as decreasing
trends in NPP in the 62 large marine ecosystems over the last decade, with New
Zealand in the middle of the decreasing half.
Climate change and the New Zealand marine environment 32
Figure 8. Global Net Primary Production (NPP) estimated from the Vertically Generalized Production Model of Behrenfeld & Falkowski (1997) and based on MODIS satellite ocean colour data. Data shown are the log-average values for July 2002 – October 2006. White lines indicate boundaries of the 64 “Large Marine Ecosystems” of the world as used by organisations including World Conservation Union (IUCN), Intergovernmental Oceanographic Commission of UNESCO (IOC), and US National Oceanic and Atmospheric Administration (NOAA), and publications including Duda & Sherman (2002).
6.1.4 General conclusions
Net primary production in New Zealand is close to the global average for marine
ecosystems which support significant fisheries. Our ocean productivity is generally
high within Australasia, but low compared with upwelling or shelf-sea ecosystems.
Changes in NPP over the world show a range of (generally small and variable)
changes over the last decade. The suggestion of a small decrease in NPP in the New
Zealand EEZ on average (1%/y) is within the global envelope. The high interannual
variability in the data, lack of validation to date, and relatively short length of the time
series means that these changes should not be considered definitive or likely to
continue. The changes are extremely unlikely to be affected by local New Zealand
human activities, and more likely to be connected to variability in climate-related
processes (see discussion of processes affecting algal blooms, Section 6.2). Validating
the satellite estimates of NPP, monitoring medium and long-term changes in NPP, and
continuing to investigate the climate-ocean-ecosystem processes which may affect
NPP are important to determine if the changes are genuine, and to understand why the
changes may be occurring.
Climate change and the New Zealand marine environment 33
6.2 Algal blooms
Microalgae are tiny, free-floating marine plants. Physical conditions such as water
temperature, light, and nutrients are the main parameters which regulate their growth.
When the conditions are right (e.g., favourable temperatures, optimal light, plentiful
nutrients), these microscopic algae can grow rapidly and build up to very high
concentrations in a matter of days. This population explosion is commonly referred to
as an algal bloom. Most blooms are harmless and contribute to ocean primary
productivity, but a few algal species can be harmful. The build-up of these species,
known as a harmful algal bloom, can cause human illnesses and damage marine
ecosystems.
In New Zealand numerous blooms occur each year. Most happen either in spring or
autumn. Many of these probably go unnoticed. But from time to time some of them
become visible either through strong displays of surface discolouration (Chang 2000,
2003) or because of their direct impacts on marine life and the environment (e.g.,
Chang et al. 1995; Chang 1999; Chang & Ryan 2004).
6.2.1 Observations of short-term ‘climate change’ on algal blooms
In New Zealand there is now ample evidence that major, large-scale, alongshore algal
blooms occurred during periods of “unusual weather” (Chang and Uddstrom 2002).
Most notably these are shorter-term oscillations on scales from a few years such as El
Niño/Southern Oscillation (ENSO) to tens of years such as Interdecadal Pacific
Oscillation (IPO). The IPO has a positive (warm) and negative (cold) state. The
climatic shift to a new state of IPO (from positive to negative values) and interaction
of this with El Niño/La Niña events seems to influence the nature of algal blooms
(Chang and Mullan 2003). Generally, the shift from neutral to either the cold (El
Niño) or warm-phase (La Niña) with a temperature anomaly of 1 to 2°C (either
positive or negative) can occur short-term for a few months to over a year, which may
be exacerbated by a change of IPO state.
Typical El Niño conditions in New Zealand are accompanied by the general
strengthening of westerly winds, and also more frequent and stronger south-westerly
and/or north-westerly winds on the western coast of South Island and north-eastern
coast of North Island respectively. South-westerly winds may drive along-shelf
upwellings on the western coast of South Island (Heath and Gilmour 1987; Viner &
Wilkinson 1987; Shirtcliffe et al. 1990) and north-westerly winds on the north-eastern
coast of North Island (Sharples 1997; Zeldis et al. 1998; Black et al. 2000; Chang et
al. 2003b). Increases in frequency and strength of these winds in spring and summer
are expected not only to strengthen along-shelf upwelling particularly in these two
Climate change and the New Zealand marine environment 34
major coastal systems, but also to contribute to the general cooling of sea surface
temperature (SST) throughout New Zealand (Figure 9). Coastal currents (e.g.,
Westland, East Auckland Currents) might also play a part in driving along-shelf
upwelling (Stanton 1976; Shirtcliffe et al. 1990; Sharples 1997), but little is known
about their role during an El Niño event. Cold, nutrient-rich, upwelled water brought
to the surface from the deeper depth promotes phytoplankton growth and also
contributes to extensive blooms on west and north-east coasts of South and North
Island respectively (Bradford et al. 1986; Chang et al. 2001, 2003b).
Figure 9. January 1998 sea surface temperature (SST) anomaly relative to the 1993-1997 mean – general cooling of SST throughout New Zealand, with plumes of cold-upwelled waters (marked by arrows) detected both on the north-eastern coast of North Island and north-western coast of South Island.
It appears that in the last 20 years or so (in the positive phase of IPO, from 1978-99)
New Zealand experienced stronger and more frequent El Niño conditions than the
previous 30 years (Chang and Mullan 2003). During this period a disproportionately
high number of algal blooms were reported throughout New Zealand (e.g., Cassie
1981; Taylor et al. 1985; Chang 1988, 1999; Chang & Ryan 1985, 2004; Chang et al.
1989, 1995, 2001, 2003a; Rhodes et al. 1993; MacKenzie et al. 1996, 2002). Most
notably a large number of these blooms were either associated with outbreaks of
marine life kills (Taylor et al. 1985; Chang & Ryan 1985, 2004) or shellfish poisoning
(Chang et al. 1995, 1996; MacKenzie et al. 1996) on the northeast coast (Figure 10).
With the exception of the 1983 blooms which were dominated by diatoms, the rest
were dominated by dinoflagellates. In the 1998 toxic outbreaks, increased transports in
Climate change and the New Zealand marine environment 35
the East Auckland Current and East Cape Current were observed (P. Sutton, pers.
comm.) and these were suggested to have contributed to the spread of a marine life
killing dinoflagellate species further south along the central east coast of New Zealand
(Chang et al. 2001).
Figure 10. Major nuisance/harmful algal blooms reported from 1950 to 2002: s, nuisance ‘slime’ events; A-I, other major HAB events. IPO phases (both negative and positive) are marked. (see The Climate Update, May 2000, October 2000, and November 2003 for discussion of the IPO)
Typically, La Niña conditions are accompanied by more frequent and stronger north-
easterly winds and result in warmer than usual surface waters around New Zealand
(Fig. 11). From 1950 to 1980, the warmer than usual conditions during La Niña
appeared to strengthen in the negative phase of IPO (Figure 10) (Chang and Mullan
2003). Warming also leads to thermal stratification and hence water-column stability.
The warmer than usual conditions in coastal waters during La Niña events are
expected to decrease nutrient fluxes from deeper waters into the euphotic zone and
thus slow down phytoplankton growth. These cause phytoplankton biomass
(chlorophyll a) to be drastically reduced around New Zealand, particularly in the two
major coastal upwelling systems in summer (Chang unpubl. data). North-easterlies
could conceivably enhance upwelling on the North Island east coast south of East
Cape, but no data exist to verify this.
Elevated water temperature would affect both the seasonal composition of the
phytoplankton and probably bring the spring/summer-blooming species (e.g.,
favouring dinoflagellates) forward to form blooms in winter/spring. In the past 50
years or so, the most notable outbreaks associated with massive build-up of slime
Climate change and the New Zealand marine environment 36
occurred in late winter and spring, and sometimes in summer during La Niña events
(Chang & Mullan 2003). Some of these outbreaks were associated with a slime-
producing dinoflagellate (MacKenzie et al. 2002) (Figure 10). Another major
dinoflagellate species which was associated with harmful algal blooms (PSP) during
the La Niña event started in winter, extended through spring and ended in early
summer (MacKenzie & Adamson 2000; Chang et al. 2003).
Figure 11. January 1999 sea surface temperature (SST) anomaly relative to the 1993-1997 mean. Warming (marked in arrows) occurred during the 1999 La Niña event in most parts of New Zealand, in particular on the northeast and central east coast of the country.
6.2.2 Projected climate effects on algal blooms in New Zealand
The predicted changes in the New Zealand region are: a temperature rise of approx.
1°C, an increase of westerly winds at higher latitude, south of New Zealand
particularly in winter/spring, and strengthening of north-easterly winds in summer. It
is anticipated that a more “La Niña-like” condition will prevail (Mullan pers. comm.).
As temperature is just one of several factors that regulate growth, temperature as such
may not be the dominant factor in phytoplankton response, in particular if the
magnitude of the rise is predicted to be about 1°C (Roemmich et al. 2007).
Climate change and the New Zealand marine environment 37
Since 2000 the IPO index has continued its downward trend, from positive to negative
(Mullan pers. comm.). It is anticipated that in the next decade or so La Niña events
will become stronger and more frequent if the IPO stays negative. Thus nuisance
‘slime’ outbreaks are expected to occur more frequently in some parts of the country,
especially when the warm “La Niña-like” conditions experienced in the future are
exacerbated by more frequent, stronger, ‘true La Niña’ events. In summer the
predominant north-easterly winds will reduce upwelling and result in warmer than
normal temperature over much of New Zealand. This in turn results in decreased
nutrient fluxes from the deep into the upper water column. Hence in summer very few
algal blooms are expected, in particular in the two major coastal systems on both the
north-eastern and western coast of North Island and South Island respectively.
In the last 50 years or so only one toxic outbreak, dominated by Gymnodinium
catenatum was reported during the 2000 La Niña event (MacKenzie & Adamson
2000; Chang et al. 2003). Given that cysts produced by G. catenatum are now found
virtually in all ports and harbours of the entire North Island (Chang et al. in press), in
the La Niña-like condition PSP blooms dominated by this species are expected to
become more common. Besides the direct effect of elevated temperatures, in La Niña-
like conditions PSP-producing dinoflagellate might bloom earlier (changes in seasonal
succession) and migrate faster to new areas as coastal currents are expected to
strengthen in some parts of the country. It is also likely that this species might spread
to higher latitudes in some parts of South Island (change of biogeographical
boundaries). As increased temperatures often cause increased stratification in the
upper water column which favours dinoflagellates (Chang et al. 2003), it is anticipated
that this group of flagellated phytoplankton could dominate in most of the blooms.
Another common feature accompanied by La Niña is wetter conditions in the north.
Cyst beds and low salinities are probably necessary to initiate the PSP-producing
Alexandrium minutum bloom (Cannon 1989). It is anticipated that in the future La
Niña-like conditions, freshening of nearshore waters might increase germination rate
of cysts of A. minutum, and thus initiate blooms a little more often on the northeast
coast (Chang et al. 1996).
6.3 Vulnerability to invasive species
New Zealand is subject to a continuous influx of foreign marine species arriving
through international shipping (Coutts & Dodgshun 2007), several of which have
already become established in our coastal waters (Cranfield et al. 1998; Willis et al.
1999; Francis et al. 2003). Between 2005 and 2007, more than 430 marine species
(many non-indigenous) were collected from merchant, fishing, cruise and recreational
Climate change and the New Zealand marine environment 38
vessel hulls in NZ ports. These originate from a variety of geographic areas and
climates, and thus it is likely that changing climate conditions will not alter the general
level of vulnerability to bioinvasions. It has recently been suggested that the greatest
effects of climate change on biological communities may be due to differences in
summer temperature maxima and winter minima (Stachowicz et al. 2002). If earlier
projections in this report (Section 5) are reasonable, we may expect an increase in the
number of invasive taxa of tropical and subtropical origin in northern New Zealand.
The corollary of this phenomenon is that the range of cold-temperate invasive species
such as the laminarian kelp Undaria pinnatifida should contract southward (Thornber
et al. 2004).
6.4 Vulnerability to disease and parasites
Warming SST may introduce the possibility of new parasites, diseases and vectors of
disease arriving in New Zealand waters, which may have implications for the fishing
and aquaculture industries as well as the structure of natural systems. In an acidifying
ocean, calcifying organisms will have to devote increasing amounts of energy and
metabolic activity to maintenance of their calcium carbonate shells, making them
more vulnerable to disease and parasites.
Recent reviews indicate trends towards increased frequencies of outbreaks in
invertebrate taxa (Ward & Lafferty 2004). Disease dynamics of marine organisms and
their consequences on population dynamics are not well understood, and in New
Zealand research effort has been focussed primarily on commercially exploited
species and those cultured in the aquaculture industry. Little knowledge is available to
predict the effects of pathogens on habitat-forming taxa.
7. Potential indicators
The following suggestions are given bearing in mind that effective indicators are those
taxa or habitats that exhibit sensitivity to changes over measurable time scales. A
recurring theme in this report is that climate trends are detectable over decadal time
scales or more, whereas natural variability over shorter time scales is high (e.g.
through ENSO events, Pacific interdecadal oscillations, or natural variability between
years). Selecting suitable indicators is an exercise constrained by understanding of the
tolerance of individual taxa to natural variability, and the likelihood of climate-
induced shifts occurring that exceed those tolerance levels. If the rate of climate
change accelerates (as has been predicted), this task will become easier, but a long-
Climate change and the New Zealand marine environment 39
term commitment to consistent monitoring programmes is required if changes are to
be detected and quantified.
7.1 Sea level
Indicators of the impacts of SLR are likely to be localised vertical zonation range
reductions of ephemeral short lived species. These may be most evident at locations
where species are already physiologically stressed due to anthropogenic impacts
derived from for example deforestation, erosion, industrial developments and
agriculture runoff. Determining the magnitude of the effects of SLR in such locations
may however be futile or prohibitively expensive to test because of the difficulty in
establishing relevant controls for valid comparisons.
Seagrass beds are likely to become more fragmented leading to their decline in some
areas. This will be due to a range of potential impacts arising from climate change
including: SLR (as above); reduced light levels resulting from SLR, increased
turbidity (greater wind/wave forces); competition from mangroves; increased
eutrophication from increased runoff leading to increased competition with
phytoplankton and synergistic reductions in light levels; and increased physical
disturbance (Turner & Schwarz 2006, Kemp et al. 2005, Short & Neckles 1999). This
fragmentation will have wider ecosystem impacts leading to changes in macro-
invertebrate abundance and diversity which differ between dense and sparse Zostera
beds (Mills 2006) and also reduced secondary production (Hailes 2006).
7.2 Wind and rainfall
Physical indicators of climate change are likely to be increases in sedimentation and
wave climates (west coast), and decreases in water clarity and salinity (freshwater
flux). These are likely to lead to increased frequency and duration of stratification
events, especially those driven by freshwater flux. Biotic indicators are likely to be
sudden sharp regime shifts (Folke et al. 2004). For example, in Chesapeake Bay, USA,
a benthic primary production system shifted to phytoplankton-dominated primary
production (Kemp et al. 2005). This change can, in extreme cases, lead to anaerobic
dead zones developing adjacent to highly eutrophied discharge points during periods
of stratification (Kemp et al. 2005). Impacts on a few leverage species or ecosystem
engineers (Coleman & Williams 2002) could also lead to trophic cascades. Episodic
sedimentation events have the potential to cause large changes in reef systems with
increasing frequency and intensity, and key structuring organisms such as kina may be
directly impacted at local scales (Walker 2007).
Climate change and the New Zealand marine environment 40
Storms can also affect seaweeds like Carpophyllum flexuosum which prefers more
sheltered conditions. This seaweed has become more abundant in north-eastern New
Zealand in the last 30 years correlated with significant decrease in storm frequency
over that period (Cole et al. 2001; de Lange & Gibb 2000). Increasing severity of
storms could therefore lead to localised reductions of this species in locales
susceptible to the effects of climate change.
7.3 CO2 and acidification
Carbon dioxide increases and consequent lowering of pH will be strongly felt in
surface waters of the Southern Ocean. It is therefore most likely that any effects of
acidification will be felt in calcareous organisms in southern New Zealand, especially
those that utilise aragonite. Potential biological indicators may include coralline algae
on shallow reefs, planktonic pteropod molluscs in the Southern Ocean, and
brachiopods and red corals in Fiordland.
Baseline surveys of calcifying organisms in NZ waters are urgently required. These
should be added to existing time-series studies and, where possible, augmented by
remote-sensing technologies. For example, remote sensing of coccolithophores is now
practical in the surface ocean which offers a mechanism for hind-casting and future
monitoring of spatial and temporal abundance in NZ waters.
Over long timeframes many organisms might be expected to be affected by sustained
changes in pH. Metabolic efficiency and growth will be impaired even in species that
use calcite rather than aragonite. Recent work has shown that pH levels below 7.5 may
be fatal for marine bivalves (Michealidis et al. 2005), so monitoring the health and
shell structure of the cultured mussel Perna canaliculus may provide a simple means
of signalling biological changes brought about by increasing acidity.
However, manganese and iron in the periostracum of a mollusc can act as a defensive
buffer against degradation from acid conditions (Swinehart & Smith 1979). It is
conceivable that increasing seawater acidity may prompt the uptake of these metals by
marine molluscs. However lower pH does also mobilise potentially toxic trace metals
such as aluminium.
In sub-tropical waters (which occupy > 40% of the NZ EEZ) the positive response of
Trichodesmium may be monitored using remote-sensing algorithms tuned to this
species (Trichodesmium is positively buoyant and forms large surface blooms).
Climate change and the New Zealand marine environment 41
7.4 Ocean warming and currents
Although overall ocean warming effects are, according to model runs, less likely to be
strongly felt in northern New Zealand relative to more southern latitudes, the reef fish
fauna of the northland east coast and offshore islands have been demonstrated to be
sensitive to incursions of subtropical water masses (Choat et al. 1988; Francis &
Evans 1993; Denny et al. 2003). Monitoring of these assemblages can give a clear
signal of the relative strength and longevity of these events, which can then be used to
examine effects on habitat-forming components of reef assemblages.
Little is known about reef fish assemblage dynamics in the South Island. The best
sources of information may be available from as yet unpublished marine reserve
monitoring reports that provide a time series of observations at certain locations.
It is well known that the distributions of tunas and large game fish are determined by
the position of warm water masses, although the position of upwellings that
presumably increase productivity and other variables also play a part (e.g. Holdsworth
et al. 2003; Willis & Hobday 2007). Examination of annual and seasonal trends in
catch rates of large pelagic predators from commercial and game fishing records may
provide an overview of large-scale changes in productivity in New Zealand shelf
waters.
Other sentinel species that may prove useful for monitoring purposes for detecting
consistent temperature effects might include cool-water algae such as Macrocystis
pyrifera, which would be expected to disappear from the northern limits of its range.
Long-lived sessile invertebrate species such as corals may provide long-term records
(through growth patterns and chemical analyses) of historical changes in temperature
that may partially mitigate the dearth of long-term monitoring data.
8. Research gaps and priorities
8.1 Summary of future work needed to improve climate modelling predictions at varying spatial and temporal scales
With every new IPCC Assessment Report comes a suite of new GCM output datasets
generated by the latest generation of climate models. The frequency of Assessment
Reports is approximately every 6 years, thus we can expect to update the AR4-derived
Climate change and the New Zealand marine environment 42
projections for New Zealand around 2013. There is still quite a lot of inter-model
variability, particularly at the New Zealand scale. With refinements to and increased
resolution of GCMs this variability is likely to reduce.
The statistical down-scaling methodology (Mullan 2001a) has not changed over the
last 7 years. However, the resolution of the down-scaled data has changed. The
resolution is now 0.05° lat/long (approximately every 5 km), matching the interpolated
“virtual climate station data” resolution (these virtual station data are now used for the
down-scaling compared with a set of 58 temperature and 92 rainfall stations in the
2001 analysis).
A significant development at NIWA is the recent capability to run a regional (as
opposed to global) scale climate model (RCM) for New Zealand. Modern climate
models represent as accurately as possible the conditions and forces which influence
the climate. Our regional model is ‘nested’ inside the UK Met Office’s global model,
but produces much more detailed results over New Zealand. The resolution of the
model is 30 km and the model domain covers most of the EEZ. Recently NIWA used
the model to simulate New Zealand's climate from 1970 to 2000 and found it
accurately reproduced the average regional distributions of temperature and rainfall of
that time.
This year, NIWA produced the first climate change simulations using the RCM for
New Zealand. One of the advantages of a regional climate model (over statistical
downscaling) is that it provides daily or even hourly data – essential for looking at
short, sharp events like intense downpours where we want to know how the return
periods may be changing.
We used a moderately high and a moderately low greenhouse gas emission scenario to
span a reasonable range of possible futures, and ran the model for the 30-year period
2071–2100 inclusive. The results are still being analysed but temperatures rise, heavy
rain increases, and snow cover shrinks under both scenarios. We can feed climate
change model results into riverflow models, notably NIWA’s TopNet, to look at the
downstream implications including flood frequency and intensity, and the effect of
climate change on sedimentation and water quality.
Climate change and the New Zealand marine environment 43
8.2 Ocean warming and currents
8.2.1 Models
The coupled atmosphere-ocean global climate models do not include enough detail to
show the narrow ocean currents that flow around New Zealand. This means that no
quantitative statements about these climatic features can be made at this stage.
However, the model technology is now maturing to the level where the models are
sufficiently accurate and have high enough resolution that detailed examinations of the
predictions around New Zealand would be useful.
8.2.2 Observations
There are a very limited number of time series of ocean data; this is particularly true of
the subsurface. The two longest subsurface time series around New Zealand are
temperature measurements between the surface and 800m along commercial ship
tracks between Auckland and Suva/Honolulu (1987-present) and Sydney-Wellington
(1991-present). It should be noted that neither of these programmes are NZ instigated
nor led, although NIWA has been collaborating since the mid-1990s.
Apart from that, there are sea surface temperature (SST) measurements at two
locations: Leigh Marine Laboratory (University of Auckland) and Portobello (Otago
University) since 1967 and 1953 respectively. High resolution satellite measurements
of SST have been archived in the NZ region since 1989.
Satellite measurements of sea surface height, which are very useful for circulation and
heat content analyses began in 1992. A limitation of these measurements is that they
lack resolution on the continental shelf.
The global programme of drifting profiling floats (Argo) is now providing very
valuable information about the upper 1000-2000 m of the world’s oceans, but
significant coverage in the South Pacific dates back to only 2002, and it is only since
2004 that there has been adequate coverage for detailed analyses. Argo is a blue-water
programme and will not provide information in shelf/coastal regions, but will help to
assess variability and change in oceanic events which drive coastal processes.
There is an even worse lack of chemical and biological time series. There have been
moorings maintained and measurements made at two locations north and south of
Chatham Rise (in subtropical and subantarctic water) since 2000. There has been an
Climate change and the New Zealand marine environment 44
ongoing study of the Hauraki Gulf since 1996 that is starting to provide insights into
the function of shelf systems in that region (Zeldis 2004; Zeldis et al. 2004).
It is almost impossible to fund and maintain time series observations in the current
funding regime. Note that our four longest time series are either supported by student
volunteers or overseas funding. Without collecting time series it is impossible to
assess past changes or make future predictions in anything but the broadest sense.
Unfortunately at least a decade of data is normally necessary to interpret variability
and there is no sign of any commitment to supporting such long-term measurements.
Remotely-sensed data will become more useful (SST, SSH and Ocean Colour).
Unfortunately these data alone are normally not adequate to understand key processes.
The Argo programme will provide much-needed subsurface information (although not
over the continental shelf: i.e. much of the region of interest for ecology, and to date at
least, not chemical or biological).
There is also a total lack of supporting and linking information. As an example, the
warming conditions in the Tasman in the late 1990s provoked interest as to what
impact they could have on the food chain and, in particular, on the hoki stocks which
declined through that time period (Francis et al. 2006). Unfortunately, there were no
data collected on nutrients or biology (e.g. the food chain) through that time period
making any impacts of the physical changes very hard to gauge.
8.3 Mitigation of anthropogenic impacts to build resilience to climate change
Given that most of the changes due to climate change are likely to be exacerbated by
anthropogenic impacts, restoration efforts of keystone species and important habitats
should be given highest priority to build more resilience into ecosystems (Folke et al.
2004) to cope with the effects of climate change. To illustrate the complexities of this
task, we give an example of restoration of seagrass beds in Chesapeake Bay in the
U.S. Restoration of seagrass there, has been hampered by a range of non-linear
ecological feedback mechanisms (Kemp et al. 2005). In an unmodified benthos,
enhanced particle trapping and sediment binding associated with benthic plants
(seagrass, microalgae) help to maintain relatively clear water columns, allowing more
light to support more benthic photosynthesis. Restoration or degradation can be driven
either way by positive-feedback mechanisms. Enrichment creates turbidity, leading to
the decline of benthic plants, allowing more resuspension, decreasing light further
stressing benthic plants. Also, nutrient-enhancement stimulates phytoplankton growth
and their subsequent sinking supports increased benthic respiration leading to anoxia,
which causes more efficient benthic recycling of nitrogen and phosphorus which
Climate change and the New Zealand marine environment 45
supports further algal blooms and so on. Initial seagrass restoration efforts failed
without parallel oyster population restoration. Oysters are reported to provide negative
feedback control on eutrophication by reducing phytoplankton biomass and increasing
water quality, allowing the seagrass beds to recover (Fulford et al. 2007).
These efforts to manage and reverse areas of anoxic conditions and ecosystem
collapse not yet evident in New Zealand, have shown that removal of nutrient and
sediment contamination is not enough to restore communities. Rather, concomitant re-
introduction of keystone species is necessary to provide bio-feedback mechanisms to
reverse the effects of eutrophication and sedimentation to restore biodiversity,
community functions and processes. This will be essential for building ecosystem
resilience to cope with climate change effects. The trophic role of suspension-feeding
bivalves in shallow ecosystems cannot be underestimated, as they can exert both
bottom-up (algal grazing) and top-down (zooplankton grazing) control on the pelagic
food web (Nielsen & Maar 2007).
Soft sediments account for a significant portion (>70%) of shallow (<60 m depth)
continental shelf New Zealand habitats, and these euphotic depths are highly
productive in terms of supporting shellfish and fin-fisheries. After more than a century
of increasingly detrimental fishing practices and ever-increasing anthropogenic
growth, large areas of these soft sediment communities have been severely modified
(e.g. homogenised), by dredging and fishing (Thrush et al. 1995), physical
disturbance, sedimentation (MacKenzie & Adamson 2004) and eutrophication. These
impacts have been so pervasive that there are very few refuges remaining offering
glimpses of these communities in their unmodified state (Pauly 1995; Kirby 2004).
The impact on dependant fisheries is manifest in the cyclical boom and bust of
shellfisheries like oysters (Nell 2001) and scallops, and likely long-term changes in
finfish community compositions and flow-on food chain effects (Handley 2006).
Notwithstanding the general lack of knowledge of marine biodiversity, assemblages,
species biology, and species interactions in New Zealand waters, our confidence in
being able to predict the impacts of climate change is severely limited. For example,
we know very little in New Zealand about the processes structuring rocky reef
communities. One view is that top-down predatory and grazers structure reef
communities which in turn affect fish and invertebrate recruitment and survival. The
alternative hypothesis is that bottom-up processes via nutrient supply and primary
production pathways structure these communities, which in turn are affected by
anthropogenic eutrophication in some catchments. Overseas studies, as illustrated
above, have shown that eutrophication of coastal ecosystems can lead to trophic shifts
away from benthic primary production towards pelagic primary productivity, which in
Climate change and the New Zealand marine environment 46
extreme situations can lead to algal blooms and anoxia especially if the water column
is stratified (Kemp et al. 2005). The antithesis of this model is that predators are
controlling grazers which in turn structure rocky reef communities (Babcock et al.
1999; Valiela et al. 2004). For example, the sea urchin Evechinus chloroticus plays a
disproportionate role in structuring New Zealand reefs (Andrew 1988; Shears &
Babcock 2002) by removing macroalgae (Schiel 1982), which in turn influence
grazing by fishes (Andrew & Choat 1982; Choat & Ayling 1987). Until we know
more about these fundamental processes in New Zealand, we cannot predict the
impacts of climate change.
8.4 Prediction of the effects of climate change – key questions
Understanding and predicting the biological effects of climate change in the marine
environment are to some extent hamstrung by the high degree of uncertainty
surrounding predictions of the variability in primary drivers: sea level, acidification,
wind, current, and temperature. Even so, a series of scenarios based on changes in
these variables would be possible to generate if relationships between them and
specific biological processes were known. Although large-scale correlations have been
identified (e.g. between sea surface temperature and the recruitment of exploited fish
stocks), it is still uncertain which processes operate on which life history stages to
produce the correlations. The only exception is that of snapper Pagrus auratus
recruitment, which Zeldis et al. (2005) have tied (with very strong correlations) to
better food supplies in warm years, leading to more competent larvae that are less
subject to predation.
Part of the problem is a lack of significant time series data that can be used to monitor
biodiversity and map population dynamics of indicator species to environmental
conditions. Estimates of demography generally exist only for commercially-exploited
species that must be monitored for stock assessment purposes. Marine reserves may
have a key role in monitoring as the only environments not potentially directly
impacted by fishing activities, although at the present time they represent only coastal
habitats at small spatial scales. To be really effective tools they must be implemented
at appropriate spatial scales and represent all habitat types (Willis & Millar 2005).
Fundamental research to building resilience and managing and restoring of inshore
habitats includes addressing:
1. Determining key species and their ecosystem services required to restore or
build resilience into ecosystems to better cope with climate change in a New
Zealand context, by comparing impact and non-impact sites
Climate change and the New Zealand marine environment 47
2. What are the thresholds of stress for direct/indirect effects (tolerance ranges)
that tip the balance for keystone species?
3. Determine the requisite recovery timescales and size of reserve/fishing closure
areas needed to effectively restore key species/ecosystems to manage effective
restoration.
This knowledge will provide managers with better tools to manage inshore coastal
communities and dependent fisheries to ensure appropriate use whilst preserving
community stability to cope with climate change.
In terms of making predictions and constructing scenarios that can assist risk
assessment and environmental management in the face of climate change over the next
century, the following research questions should be addressed:
• Which species are most at risk, and consequently, which functional groups
and ecosystems are most sensitive?
• What is the baseline against which any changes can be assessed? That is,
what is the range of natural variability in physical and biogeochemical
systems at the present time?
• What are the natural tolerances of key species and/or major taxonomic
groups to changes in various predicted stressors to provide scenarios in
impact prediction?
• What are the rates of change in key ecosystems and what is the adaptive
potential key groups have to varying rates of change?
• How do the expected changes impact on the diversity, species mix,
population dynamics and functionality of large scale biogeochemical
processes, including primary productivity?
• What interactions might occur between climate-related stressors and the
energetic budgets of marine species and ecosystems?
• How might existing sources of anthropogenic disturbance interact with
projected climate changes to exacerbate problems?
Climate change and the New Zealand marine environment 48
• How vulnerable are New Zealand’s economic activities in the marine
environment – especially wild fisheries, aquaculture, and tourism – to
climate change in the short to medium term?
• Can local anthropogenic impacts be meaningfully separated from the
direct effects of climate change? And if not, should resilience
building/mitigation of potential impacts be more important priorities?
Although climate change is a gradual process that occurs on decadal time-scales, one
of the likely effects is an increase in the frequency of extreme events: abrupt changes
in weather systems that have immediately measurable consequences (Jentsch et al.
2007). These are evident on land, but may not be quite so apparent in marine systems.
At large scales, sudden shifts in marine current systems can alter whole ecosystems
(Francis et al. 1998; Anderson & Piatt 1999). Possibly one of the most rewarding
approaches to obtaining empirical estimates of the potential effects of warming New
Zealand seas may be to institute a monitoring programme aimed at quantifying the
variability brought about by La Niña events. Although the effects of ENSO
oscillations tend to be short term (one to two years), changes seen in present day La
Niña conditions may represent mean conditions in 50-80 years. Key systems for
monitoring purposes might include, for temperature change: east Northland and the
Hauraki Gulf in the north, and Tasman/Golden Bay in the south; for acidification:
Fiordland and Stewart Island systems, with emphasis on calcareous organisms; for
sedimentation: representative rocky reefs throughout the country, shallow soft
sediment systems in enclosed waters subject to high anthropogenic inputs, soft
sediment systems on the exposed west coasts of both North and South Islands; for sea
level effects: mangrove and seagrass dynamics. Over shorter time frames,
experimental manipulations of sediment influx events on reef fauna (e.g. Schiel et al.
2006), mechanical stress on algae and sessile animals expected under severe storm
conditions (Hurd 2000; Harder et al. 2006), and varying light regimes on productivity
of algal assemblages may prove fruitful. These experiments need to examine the
cumulative effects of varying frequencies of extreme events to determine the resilience
of our systems.
Our success in mapping biological mechanisms to large-scale correlations will
probably improve by refining the spatial resolution of individual environmental
studies. This means that detailed environmental data must be collected at local scales,
including sea temperature, wave heights, tidal heights, current patterns and interannual
or seasonal variability in current strength, upwelling systems, and primary and
secondary productivity. Detailed monitoring effort spread throughout the New
Zealand EEZ will give much more confidence in our ability to face future change and
Climate change and the New Zealand marine environment 49
deal with its consequences. We need to keep in mind the extent to which coastal
processes and events are driven by large scale oceanic influences, and maintain studies
which enable a better understanding of these surrounding oceanic drivers.
Research priority should be given to initiating long-term monitoring studies for those
oceanographic features for which data are currently lacking, and for characterising
biological assemblages and their natural variability at a national scale. Such a
programme is open-ended by nature and does not have specific goals, and thus will
not meet the criteria usually imposed for short-term research funding. It is, however,
imperative to possess such data if shorter-term experimental work is to be validated,
and to interpret the changes brought about by climate change so that effective
management interventions can be implemented, where warranted. Time series data in
the natural environment usually do not begin to have predictive power before at least
ten years have elapsed, but do provide information that forms the basis of more
specific experiments of shorter duration. Predicted climate changes over the next few
decades are relatively small, and thus are difficult to simulate effectively in
manipulative experiments. A first step would be to collate and coordinate existing
monitoring and measurement programmes with a view to identifying critical gaps.
Priority for short-term experimental work is likely to be driven by feasibility, but
should be concentrated on determining the effects of likely known impacts (e.g.,
temperature, pH, sedimentation) on influential taxa within different biomes.
Identification of these taxa is critical to progress in determining future ecosystem-wide
effects of incremental changes in climate.
9. Conclusions
There is considerable uncertainty not only in the direct consequences of
anthropogenically-induced (or anthropogenically-accelerated) climate change in the
marine environment, but also in the range of biological responses and tolerance to the
predicted changes. We are constrained to a large extent by limited knowledge of the
responses and tolerances of key species to changing environmental conditions as well
as a poor understanding of existing ecosystem dynamics. The dynamics of relatively
well-studied species are still not predictable with regard to changing climatic
conditions. For example, evidence linking the population dynamics of commercially
exploited fish species with large scale climate variability is generally still indicative,
rather than predictive in the New Zealand region (e.g. Francis et al. 2006; Willis et al.
2007). This situation arises partly because of strong interannual variability between
variables (e.g. in recruitment strength, weather patterns), meaning that correlations
often only appear on decadal time-scales for which time-series of suitable data are
Climate change and the New Zealand marine environment 50
rare. This variability is added to by unmeasured variance – many of the drivers of a
species population dynamics operate on smaller spatial scales than can be easily
measured. For example, a fish population may have a strong year class at the
population level because of a chance encounter between larvae and a patch of plankton
sustained by a short-term, local upwelling event. Temperature per se may be
positively correlated with many biological phenomena only indirectly.
In some cases, negative effects of climate change caused by one factor may be
counterbalanced by changes in another. For example, drowning of mangrove forests
by rising sea levels may be offset by increased rates of sediment accretion brought
about by terrestrial flood events. The likelihood of local extirpation of a particular
species will therefore vary at local scales that are much smaller than the limits of
current climate models. It is thus difficult to suggest whether particular areas are likely
to be more or less prone to major ecosystem shifts.
Some general predictions can be made at larger scales, however. The increasing
likelihood of drought in eastern regions along with a higher incidence of extreme
weather events indicates that eastern coasts are likely to be subject to episodic inputs
of terrestrial sediments. These will smother coastal shelf habitats. Whilst work in
Northland has shown that episodic sediment influxes can have large effects on
estuarine systems (Thrush et al. 2003, 2004), little experimental work has dealt with
sedimentation effects on coastal reefs or deeper soft-sediment systems (Airoldi 2003),
and less still is known about recovery rates.
Northern New Zealand is likely to be subject to a strengthening of the East Auckland
Current that should establish a greater number of tropical or subtropical species in the
region. Many of these species currently occur as vagrants in La Niña years or recruit
seasonally but do not form breeding populations. This area will also become more
vulnerable to human-mediated invasions of exotic species from warm biomes, but will
become less vulnerable to invasion from colder-water invasives such as the kelp
Undaria pinnatifida.
General southward shifts in species ranges are expected. Species with cooler water
affinities will become locally rare or extinct in the north. Major oceanographic
features are not expected to change position, but will strengthen or weaken depending
on large-scale ocean climate.
The general and limited nature of these predictions highlights not only the paucity of
climate change-directed research on marine organisms, but also the lack of
understanding of ecological processes and systems at the present time. Experimental
Climate change and the New Zealand marine environment 51
work on key organisms is needed to make long-term predictions of how marine
ecosystems are likely to change in the medium to long-term. Indications are however
that warming scenarios will induce stressors that in the short term (ie the next 50
years) may not have large effects on their own, but may act in synergy with those
existing at the present time to exacerbate current impacts on the marine environment.
These include:
• fishing, which acts directly through removal of biomass, and indirectly
through modifications to habitats (Jennings & Kaiser 1998),
• pollution, including terrestrial inputs of nutrients (especially from farming) or
point sources of contamination (e.g. from heavy industry),
• sedimentation from terrestrial sources brought about primarily by changes in
land use (especially deforestation) and landscape modification through urban
development, agriculture, mining, or road construction.
• modification of coastal morphology through construction of structures such as
piers, or anti-erosion measures like breakwaters and seawalls.
• introduction of exotic species through human vectors such as shipping.
• The southern spread of more warm water invasive species including disease
causing species.
The most effective measures that can be taken at the present time to mitigate the
potential effects of climate change are to minimise those impacts that might reduce the
resilience of existing ecosystems. Following the above categories, immediate actions
may include:
• Reducing total allowable catches in fisheries to diminish the risk of stock
collapse due to recruitment failure3, improving the selectivity of fishing gear
to reduce bycatch, and seeking alternatives to contact fishing gears,
• Taking measures to reduce nutrient and sediment inputs to coastal ecosystems
via terrestrial watersheds,
3 Note that some exploited stocks may benefit from climate change and may not require precautionary management intervention.
Climate change and the New Zealand marine environment 52
• Stabilisation of erosion-prone catchments through reforestation, appropriate
land use, and ensuring the effectiveness of sediment traps put in place
downstream of earthworks,
• Limiting coastal development, and ensuring that coastal protection measures
do not simply displace wave energy to other vulnerable locations,
• Maintaining vigilance in biosecurity: including increased surveillance, efforts
to predict likely invasive taxa, and understanding of likely ecosystem
consequences of new introductions.
Many of these measures will have economic and social consequences, and cost/benefit
analyses are required to determine their likely efficacy under changing environmental
and economic scenarios.
In this report we have put forward some of the possible changes to the New Zealand
marine environment expected under current climate change scenarios. At the same
time, it is apparent that we lack much of the knowledge needed to make specific
predictions at scales at which appropriate management measures can be taken. This
stems from three main gaps in marine ecological research: 1) the lack of long-term
time series of data with which to establish correlations with past environmental
fluctuations; 2) a limited understanding of the way ecosystems are structured by
interactions between species and their environment; and 3) little information on the
tolerances of habitat-forming species to variability in the environmental factors that
may be affected by climate change. Recent efforts to construct a geographically
explicit marine classification in the New Zealand region (Snelder et al. 2007) may,
with model refinement and more data input, provide a basis for assessing large-scale
biogeographical shifts associated with climate change.
Climate change and the New Zealand marine environment 53
10. Acknowledgements
For the Primary Productivity section (6.1): Data used courtesy of Oregon State
University “Ocean Productivity” project. SeaWiFS data used courtesy of NASA and
Geoeye Inc. MODIS data used courtesy of NASA. This work relies significantly on
funding from the Foundation for Research, Science and Technology project
(capability fund project CRCM063: “Bio-optical properties and productivity
algorithms”, and “Ocean Ecosystems: Their Contribution to New Zealand Marine
Productivity” C01X0223).
We thank Dr Richard Feely (NOAA, Seattle, USA) for permission to reproduce
Figures 3 and 4.
We thank Kim Currie, Janet Grieve, Caroline Hart, Rosie Hurst, and Alison
MacDiarmid for contributing materials and discussion. Helpful comments on the draft
report were provided by Russell Cole, Ken Grange, Clive Howard-Williams, Alison
MacDiarmid and Don Robertson.
Climate change and the New Zealand marine environment 54
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12. Appendix 1: Projected climate change over the New Zealand landmass
Figure A1. Projected changes in annual mean temperature (in °C) relative to 1990.
Climate change and the New Zealand marine environment 77
Figure A2. Projected changes in seasonal mean temperature (in °C), for the 2030s relative to 1990: middle of IPCC range
Climate change and the New Zealand marine environment 78
Figure A3. Projected changes in seasonal mean temperature (in °C), for the 2080s relative to 1990: middle of IPCC range
Climate change and the New Zealand marine environment 79
Figure A4. Projected changes in annual precipitation (in %) relative to 1990
Climate change and the New Zealand marine environment 80
Figure A5. Projected changes in seasonal precipitation (in %), for the 2030s relative to 1990: middle of IPCC range
Climate change and the New Zealand marine environment 81
Figure A6. Projected changes in seasonal precipitation (in %), for the 2080s relative to 1990: middle of IPCC range