Marine Estate Research Report

Feasibility study – Potential locations for macro-algae farming

off East Anglian coast

© Crown Copyright 2014

ISBN: 978-1-906410-61-2

Published by The Crown This report is available on The Crown Estate website at www.thecrownestate.co.uk

Dissemination Statement This publication (excluding the logos) may be re-used free of charge in any format or medium. It may only be re-used accurately and not in a misleading context. The material must be acknowledged as Crown Estate copyright and use of it must give the title of the source publication. Where third party copyright material has been identified, further use of that material requires permission from the copyright holders concerned.

Disclaimer The opinions expressed in this report are entirely those of the authors and do not necessarily reflect the view of The Crown Estate, and The Crown Estate is not liable for the accuracy of the information provided or responsible for any use of the content.

Suggested Citation Capuzzo, E., Stephens, D., Aldridge, J., Forster, R.M. 2014. ‘Feasibility study – Potential locations for macro-algae farming off the East Anglian coast’ The Crown Estate, 37 pages. ISBN: 978-1-906410-61-

2

Feasibility study – Potential locations for

macro-algae farming off the East Anglian

coast

Authors: Elisa Capuzzo, David Stephens, John Aldridge, Rodney

Forster

Commissioned by The Crown Estate

Head office

Centre for Environment, Fisheries & Aquaculture Science

Pakefield Road, Lowestoft, Suffolk NR33 0HT, UK

Tel +44 (0) 1502 56 2244 Fax +44 (0) 1502 51 3865

www.cefas.co.uk

Cefas is an executive agency of Defra

Executive Summary

The natural populations of seaweeds (macro-algae) around the coasts of the UK have

historically been intensively harvested for use as food, soil improvers and for mineral

extraction. This activity has declined throughout the twentieth century to a very low level of

use, but there has been a recent resurgence of interest in the use of macro-algae. The larger

algae, particularly the kelps, can be used for cosmetics, food, hydro-colloids and other high-

value chemicals, fertilisers, and also as biomass for energy generation via anaerobic

digestion. In the future, with increasing demand, it is likely that algae will be harvested less

from natural populations in favour of farming of particular high value species.

The majority of the recent scientific research in the field of macro-algae farming has been

focussed on the west coast of Scotland (e.g. Aldridge et al. 2012), but achieving a wider

uptake of macro-algae in large-scale supply chains will need a range of sites around the UK

to be explored.

An earlier study by Cefas (Aldridge et al. 2012) showed that nutrient concentrations in

winter and early spring can be an important factor in determining the yield of an algal crop

during the following spring-summer growth period. Therefore it could be expected that sites

with nutrient enrichment would deliver higher biomasses of kelp at harvest, compared to

sites with similar conditions of light and temperature but lower nutrient concentration. For

this reason, and for social-economic reasons such as proximity to advanced biotechnology

facilities on land and access to a skilled labour force, the eastern coast of England could be a

promising location for macro-algal development.

The aim of this study was to provide an assessment of the suitability of East Anglian

waters for the large-scale farming of macro-algae, using a GIS-based approach to

identifying optimal sites for potential farms based on environmental data layers.

The key environmental variables, affecting growth and composition of macro-algae,

adopted in the GIS study included: minimum and maximum sea surface temperatures, light

climate (as depth at which the available light is 10% of the surface light), maximum tidal

velocity, wave height, and nutrient concentrations. The range of each environmental

variable was considered and ranked in optimal, sub-optimal, or unsuitable intervals, for

macro-algae growth. A composite layer of the rankings of the different variables was made

in order to find the sites with the highest suitability. The sites suitable for macro-algae

farming were then compared to publicly-available GIS layers of existing and planned uses

and constraints of this sea region, in order to locate areas which could potentially support a

large seaweed farm capable of producing upwards of 20 000 tonnes dry weight per year

(e.g. with dimensions 4 km by 4 km, as modelled in Aldridge et al., 2012). The layers used for

activities included current or future wind farms, planned Marine Conservation Areas, and

areas of high shipping traffic. Three potentially sites were identified, presenting suitable

environmental conditions for macro-algae growth with minimal conflict with existing uses.

The GIS-based approach of intersecting relevant layers (environmental data, constraints,

and conflicting uses) provided a useful and flexible tool for selecting suitable sites for macro-

algae farming. The composite layer of the ranking of the different environmental variables

showed that there are no sites in which all environmental variables were in the ‘optimal’

range for macro-algae growth. The highest rated areas, in terms of suitability for macro-

algae farming, were located off the north Norfolk coastline and off the Humber estuary. In

particular, three sites were selected for detailed consideration:

o Site 1 is located on the north-east of Wells-next-the-Sea; it is the deepest site and

potentially the least turbid.

o Site 2 is the least exposed to waves, and has an optimal level of nutrients during

winter; it is also the closest to port (Wells-next-the-Sea) and has the lowest

indicated vessel traffic and the least conflicts. However it is also the most turbid

site.

o Site 3 is the most northerly site off the Humber estuary; it has optimal

temperature range. This site is the most exposed with the highest maximum tidal

velocity and wave height, as well as being the furthest from port (Grimsby).

Comparison with historical species records showed that the kelp Saccharina latissima, which

is a possible target species to farm, has in the past been recorded along the Norfolk coast,

close to the most suitable sites. This lends support to the site selection procedure.

The report did not consider co-management options such as integrating macro-algae farms

with windfarms or other aquaculture options. This could be explored further to optimise

uses of sites with suitable conditions and maximise economic returns on existing

equipment. Further access constraints, such as distance to plant/processing areas on land,

as well as engineering constraints (in relation to the physical structure of the farm) could

also be taken into account to improve the site suitability selection.

Table of contents

1 Introduction ................................................................................................................................... 1

1.1 GIS-based analysis for site suitability for aquaculture ............................................................ 4

2 Methods .......................................................................................................................................... 6

2.1 Work approach ....................................................................................................................... 6

2.2 Input data ................................................................................................................................ 8

2.2.1 Sea surface temperature ................................................................................................ 8

2.2.2 Tidal velocity and wave height ........................................................................................ 8

2.2.3 Depth of light penetration .............................................................................................. 9

2.2.4 Dissolved inorganic nitrate concentration ...................................................................... 9

2.2.5 Bathymetry...................................................................................................................... 9

2.2.6 Legal and environmental constraints, competing uses ................................................ 10

2.2.7 AIS marine traffic observation ...................................................................................... 10

2.2.8 Distance to port ............................................................................................................ 10

2.2.9 Historical macro-algae observations ............................................................................. 10

2.3 Data analysis ......................................................................................................................... 11

2.3.1 Definition of optimal/suboptimal/unsuitable environmental conditions .................... 11

2.3.2 Combining layers into environmental suitability index ................................................ 11

2.3.3 Identifying potential sites ............................................................................................. 12

2.3.4 Detailed comparison of sites......................................................................................... 12

3 Results ......................................................................................................................................... 13

3.1 Environmental data ............................................................................................................... 13

3.2 Classified environmental data .............................................................................................. 16

3.3 Combined layers into suitability index .................................................................................. 18

3.4 Potential sites identified ....................................................................................................... 19

3.5 Qualitative assessment of site selection process ................................................................. 24

4 Discussion ................................................................................................................................... 26

4.1 Ranges of environmental variables ....................................................................................... 26

4.2 Site selection ......................................................................................................................... 29

4.3 Comparison with historical in situ observations ................................................................... 32

5 Conclusions and recommendations ......................................................................................... 33

6 References ................................................................................................................................... 34

1

1 Introduction

The natural populations of seaweeds (macro-algae) around the coasts of the UK have

historically been intensively harvested for use as food, soil improvers and for mineral

extraction. This activity has declined throughout the twentieth century to a very low level of

use, but there has been a recent resurgence of interest in the use of macro-algae. The larger

algae, particularly the kelps, can be used for cosmetics, food, hydro-colloids and other high-

value chemicals, fertilisers, and also as biomass for energy generation via anaerobic

digestion. In the future, with increasing demand, it is likely that algae will be harvested less

from natural populations in favour of farming of particular high value species. The majority

of the recent scientific research in the field of macro-algae farming has been focussed on

the west coast of Scotland (e.g. Aldridge et al. 2012), but achieving a wider uptake of macro-

algae in large-scale supply chains will need a range of sites around the UK to be explored.

The Crown Estate has begun to investigate the potential for large-scale production of

macro-algae and the wider ecosystem effects of large-scale extraction of these seaweeds

(kelp).

In previous work commissioned by The Crown Estate, Cefas adopted two model-based

approaches for assessing the potential environmental impact of macro-algae farms situated

in four hypothetical locations on the west coast of Scotland (Aldridge et al. 2012). In

simulations, it was found that the winter and early spring nutrient concentration in the

water was important in controlling the yield of kelp biomass during the following months. A

site in the outer Clyde estuary, with a winter nutrient concentration of 10 mmol m-3

(compared to an ambient level of 7 mmol m-3 for other sites on the west coast of Scotland),

was predicted to have a correspondingly higher potential yield of Saccharina latissima

(Aldridge et al. 2012).

Work by Drew and co-authors (e.g. Conolly and Drew 1985) at St. Andrews in the 1970s

showed that natural kelp populations in the proximity of a waste water discharge grew

faster than those located in lower nutrient water. Therefore it could be expected that sites

with nutrient enrichment would deliver higher biomasses of kelp at harvest, compared to

sites with similar conditions of light and temperature but lower nutrient concentration.

2

The winter nutrient concentrations in the southern North Sea, and the East Anglian coast in

particular, are among the highest in the UK (Hydes et al. 1999; Lenhart et al. 2010; Proctor

et al. 2003). For this reason, and for economic reasons, such as proximity to advanced

biotechnology facilities on land, the eastern coast of England could be a promising location

for macro-algal development.

The area off East Anglia is a zone of elevated turbidity, as result of the coalescing of the

Humber, Thames and Wash estuaries (Bristow et al. 2013; Dyer and Moffat 1998). This

turbid area is also known as the East Anglian plume (EAP) and it extends across the Southern

Bight of the North Sea, the Dutch sector and eventually reaches the German Bight (Dyer and

Moffat 1998). The water column in the EAP is vertically mixed and characterised by high

suspended sediment concentration, as result of coastal erosion and freshwater runoff (van

Raaphorst et al. 1998).

The Humber, Thames and Wash estuaries introduce dissolved nutrients into the coastal

waters off East Anglia; the Humber total dissolved inorganic nitrogen input is estimated at

57.4 x103 t year-1 and 95% of this is exported to the North Sea (Jickells et al. 2000). During

winter, when phytoplankton is light-limited, the EAP transports inorganic nutrients (nitrate)

towards continental Europe (10,340 x103 kgN in March; Weston et al. 2004). Contrarily,

during spring and summer, the EAP transports nitrogen mainly in the form of ammonium

and Particulate Organic Nitrogen (PON), due to phytoplankton uptake. Consequently, the

plume is an important region of the southern North Sea for nutrients processes and organic

matter (Weston et al. 2004).

Due to the high level of nutrients in the area off East Anglia, it could be expected that yields

of a farm in this location should accordingly be higher, if the other environmental conditions

(i.e. temperature, light climate, tides and waves) are also favourable for macro-algae

growth. At the same time the coastal seas of southern England are already heavily exploited

by many other users and space is at a premium (Limpenny et al. 2011).

This study is therefore aimed at identifying potential locations for macro-algae farming off

the Norfolk and Suffolk coasts (see extent of the study area in Figure 1), presenting suitable

environmental conditions for macro-algae growth with minimal conflict with existing uses.

This work does not cover regulatory constraints which may occur as a result of national or

international legislation, but would add to the information necessary for marine spatial

3

planning in the East of England (MMO 2014). The existing marine plan states “The main

issue with respect to aquaculture in the East marine plan areas is to help enable the broadly

recognised opportunity for growth in the sector and to ensure this growth is sustainable. An

assessment of the optimum sites for future expansion of the industry was identified as a

requirement (commenced by the Marine Management Organisation with published report

Marine Management Organisation 1040) along with further research into the possibility for

co-location of aquaculture with other activities, and carrying capacity of areas for

aquaculture.”

Although legislatory frameworks are in place to control the harvesting of wild macro-algae

populations in Europe, there are very few precedents for offshore seaweed farming. A

preliminary assessment of the relatively few legal documents relevant to macro-algae

mariculture is presented by Benson et al. (2014), and case studies of regulations impacting

seaweed development in Northern Ireland (Strangford Lough) and The Netherlands are

given by Parker et al. (2014; personal communication to R. Forster).

Figure 1. The extent of area investigated in this study, for identification of sites suitable for

macro-algae farming, is highlighted in red.

4

1.1 GIS-based analysis for site suitability for aquaculture

There are many examples in the literature of GIS-based analysis for site suitability for

aquaculture of fish and shellfish (see list of examples in Kapetsky and Aguilar-Manjarrez

2007; Nath et al. 2000). The application of this technique for selection of sites for macro-

algae farming is novel, therefore there are fewer examples available in literature (e.g.

Kapetsky and Aguilar-Manjarrez 2007; Radiarta et al. 2011; Rosijadi et al. 2011).

In general, a GIS-based analysis for site suitability for aquaculture aims to define sites where

the production of fish/shellfish/seaweed is maximised and the conflicts (with other

potential uses of the sites) is minimised (Rosijadi et al. 2011; Kapetsky and Aguilar-

Manjarrez 2007). The analysis uses two sets of variables:

1. selection factors;

2. selection constraints.

The first set includes all those variables that affect the potential productivity of the site (e.g.

environmental variables), while the second set include all those variables which make an

otherwise desirable site unsuitable for development (Rosijadi et al. 2011). Examples of

selection constraints could be regulations or competing uses for space (e.g. windfarms,

fishing grounds). Rosijadi et al. (2011) divide the selection constraints into access constraints

(e.g. distance to port), legal constraints (e.g. military and conservation zones),

environmental constraints (e.g. critical habitat, restoration zones), and competing uses

constraints (e.g. shipping, oil platforms, cable, dredge disposal sites, aggregates extraction).

Once selection factors and constraints are identified, they are combined together (e.g.

intersected) for identifying the most suitable areas for macro-algae farming.

Focusing on the selection factors (i.e. environmental variables), Kapetsky and Aguilar-

Manjarrez (2007) consider coastlines, winds, currents, and bathymetry for identifying

suitable sites for Gracilaria farming in northeast Brazil. For identification of sites suitable for

cultivation of Laminaria japonica in Japan, Radiarta et al. (2011) took into account sea

surface temperature, suspended solids (proxy for turbidity), bathymetry and slope of the

bottom. The authors defined suitable ranges of the different environmental parameters

based on literature and expert opinion; they also ranked the importance of the variables

from 1 (least important) to 9 (most important; Radiarta et al. 2011). Rosijadi et al. (2011)

considered in their analysis for site selection for macro-algae farming off Southern California

5

and New England: sea surface temperature, chlorophyll concentration, salinity, turbidity,

irradiance, and sea surface winds.

A final example is given in a recent report by the MMO (2013), where a broad-scale GIS

approach with four input layers (substrate type, combined seabed energy, depth and

distance from shore) was used for investigating the suitability of the east coast of England

for macro-algae farming. Water quality parameters such as turbidity, nutrients and

temperature were not included in the analysis, either because not thought to have sufficient

data coverage in the region, or because not considered important (MMO 2013).

6

2 Methods

2.1 Work approach

Based on the outcome of previous projects commissioned by The Crown Estate (Capuzzo et

al. 2012; Stephens et al. 2014) and on similar studies (Kapetsky and Aguilar-Manjarrez 2007;

Radiarta et al. 2011; Rosijadi et al. 2011; MMO 2013), the key environmental variables, or

selection factors, considered in this project are:

1. minimum sea surface temperature;

2. maximum sea surface temperature;

3. light availability (expressed as depth at which the available light is 10% of the surface

light);

4. maximum tidal velocity;

5. maximum wave height;

6. nitrate concentration;

7. depth.

Ranges of these environmental variables for optimal, suboptimal and unsuitable macro-

algae growth were identified (based on literature and expert opinion) and intersected. The

optimal/sub-optimal/unsuitable ranges were identified based on the growth requirements

of Saccharina latissima, as this species is native to the East Anglian coast and has suitable

attributes for farming (rapid growth, high energy content, edible). The resulting intersected

areas were ranked, based on the suitability score from more to less suitable for macro-algae

farming. To these suitable areas, selection constraints were then applied (e.g. windfarms,

protected areas, shipping routes).

Finally, three sites, presenting the highest suitability score and the minimum conflict with

existing uses, were identified and described in details.

The process undertaken to identify potential sites viable for macro-algae cultivation is

summarised in Figure 2. Section 2.1 focuses on the environmental data (or selection factors)

and marine usage data (or selection constraints) which were used as base for the suitability

analysis (green rectangles in Figure 2).

7

The 4 main steps of the analysis (blue rectangles in Figure 2), described in Section 2.2, were

carried out using R version 3.1 (R Development core team, 2014) and ArcGIS version 10

(ESRI, 2014).

Figure 2. Flow chart summarising the approach used for identifying sites suitability for

macro-algae farming off East Anglia.

8

2.2 Input data

2.2.1 Sea surface temperature

Daily sea surface temperature data for a 12 year period (2001-2013) was obtained from the

Ocean Sea Temperature and Ice Analysis Product (OSTIA; Donlon et al. 2012) of the UK Met

Office with delivery via the MyOcean data portal (http://www.myocean.eu/). The extreme

values of the 95% data interval (2.5 and 97.5 percentile values) were calculated on an

annual basis and used to set a temperature range (in this way it can be expected that at

least 95% of daily temperature values fell within this range). This approach was used

considering that the effects of macro-algae exposure to extreme temperatures is more

severe when exposure is prolonged; for example it has been observed that Saccharina

latissima disintegrated after exposure for 7 days at 23 °C (Bolton and Lüning 1982). In other

words, for the study area while extreme values may occur outside the specified range, these

events will be likely to persist for a short period of time.

The water column in the EAP is vertically mixed (van Raaphorst et al. 1998), therefore is

assumed that temperature values are uniform throughout the water column.

2.2.2 Tidal velocity and wave height

Wave and currents were modelled on the Southern North Sea and English Channel with a

grid resolution of approximately 2 km (1/40 degree east-west, 1/60 of a degree north-

south). Results used here were for the year 2000. Depth mean tidal and wind driven

currents were calculated using the POLCOMS model (Holt and James 2001) forced with 15

tidal constituents (Q1, O1, P1, S1, K1, 2N2, μ2, N2, ν2, M2, L2, T2, S2, K2, M4) and hourly

wind and pressure at 12 km resolution from the UK Met Office mesoscale atmospheric

model. The maximum annual current was selected as the output layer, because extremes

are more important than means in this context. Using the same meteorological forcing, the

WAM spectral wave model (Osuna and Wolf 2004) was used to provide the peak seasonal

significant wave height (Spring = March/April/May; Summer = June/July/August; Autumn =

September/October/November; Winter = December/January/February). Only autumn

values of wave height were used for site suitability analysis, considering that largest waves

usually occur in this period.

9

All other environmental variables were resampled to the same (2 km) grid as the tidal

current and wave height data so the analysis could be performed on a consistent grid.

2.2.3 Depth of light penetration

Daily maps of the light attenuation coefficient from MODIS (Kd(PAR); Gohin et al. 2002),

generated by Ifremer (Brest, France; http://www.ifremer.fr/nausicaa/marcoast/index.htm),

were averaged by month across 10 years (from 2002 to 2012). The derived Kd(PAR) for

spring (March/April/May) was used to calculate the depth of the available light is equivalent

to 10% of surface light, using Equation 1.

Ez10% = 0.1 * E0 = E0 * e-Kd(PAR) * z10% (1)

Where Ez10% is the irradiance (PAR) at depth z10%; E0 is the irradiance (PAR) just below the

surface; and z10% is the depth at which the irradiance is 10% of the surface irradiance.

2.2.4 Dissolved inorganic nitrate concentration

A compilation was made of all available measurements of water column nitrate within the

months when concentrations are highest (January to March), based on a climatology of in

situ (ship-based) measurements. The sampling stations were not equally distributed across

the study area, with more points located inshore than offshore. Kriging was used to produce

a continuous raster layer (at 0.05 degree resolution) suitable for nutrient quality

assessment.

As for temperature, it is assumed that nitrate concentration is uniform throughout the

water column.

2.2.5 Bathymetry

The bathymetry used was a 1 arc-second grid produced by Astrium Oceanwise for DEFRA

(Astrium OceanWise 2011). Although the grid was at 1 arc-second resolution (approximately

30 m), the underlying data was of a variable quality. More details on the bathymetry layer

are given in Stephens et al. (2014).

10

2.2.6 Legal and environmental constraints, competing uses

DEFRAs Marine Reference dataset (collated by the Joint Nature Conservation Committee

2011) was used to delineate restriction and exclusion zones (military practice areas,

dumping ground/disposal sites, cables/pipelines, fishing activities), offshore production

areas and windfarms. Special Areas of Conservation (SACs), Marine Protected Areas (MPAs)

and Marine Conservation Zones (MCZs, designated and proposed) were also considered.

2.2.7 AIS marine traffic observation

Marine vessel AIS (Automatic Identification System) ping data was obtained from exactEarth

Ltd. (http://www.exactearth.com/) for the year of 2013. The ping density was calculated for

each grid cell, which was then classified into quartiles (low, low-moderate, moderate-high,

high) to provide a relative scale of vessel traffic.

2.2.8 Distance to port

Port locations were obtained from the World Port Index, WPI (msi.nga.mil/NGAPortal).

Distance from the centre of each grid cell was calculated to the nearest port. Wells-next-

the-Sea did not appear in the WPI layer however observations from Marine Traffic AIS data

suggested that the port of Wells is regularly used servicing the Sheringham Shoal windfarm

off north Norfolk coast. Therefore, considering this port potentially viable for serving macro-

algae farm, it was added to the analysis.

2.2.9 Historical macro-algae observations

In situ observations of macro-algae presence were obtained from The Crown Estate (June

2014). Observations were collated by the Natural History Museum, in an ESRI geodatabase

(WGS1984) and clipped from Flamborough Head to the Thames.

11

2.3 Data analysis

2.3.1 Definition of optimal/suboptimal/unsuitable environmental conditions

The first stage of analysis (Figure 2, stage 1) was to classify the environmental data

according to conditions suitable for macro-algae cultivation. A literature search was used in

order to identify suitable thresholds (Table 1 and Discussion); this information was

supplemented with expert knowledge.

A 3 tier classification was used for each environmental variable:

unsuitable = conditions considered unsuitable for macro-algae growth;

sub-optimal = macro-algae growth is potentially viable although conditions are not

optimal;

optimal = most suitable conditions for macro-algae growth.

Table 1. Details of the thresholds chosen for each environmental variable and references.

Variable Optimal Suboptimal Unsuitable Reference

Minimum Temperature (°C) 4 2-4 <2 Bolton and Lüning (1982)

Maximum Temperature (°C) < 16 16-18 >18 Bolton and Lüning (1982)

KPAR 10% light depth (m) >4 2-4 <2 This study

Tidal velocity (m s-1) 0.25-1 <0.25 & 1-2 >2 Buck and Buchholz (2005)

Significant Wave height (m) 1-4 <1 & 4-6 >6 Buck and Buchholz (2005)

Winter Nitrate (mmol m-3) >20 10-20 <10 Aldridge et al. (2012)

Bathymetry (m) 10-30 30-50 <10 & >50 Radiarta et al. (2011)

2.3.2 Combining layers into environmental suitability index

In order to create an overall map of environmental conditions suitable for macro-algae

growth and cultivation, the classified layers produced from the step 1 of the analysis

12

(Section 2.2.1) were intersected. The suitability index is simply a count of the number of

‘optimal’ variables divided by the number of variables taken into account.

The index ranges between 0 (no variables are in the optimal range) and 1 (all variables in

optimal range). A total of 7 variables were used (Table 1); if, for example, 5 variables were in

an optimal range the suitability index score would be 5/7 = 0.71.

Only grid cells where all variables were at least ‘sub-optimal’ were considered in the next

stage of analysis, i.e. if any variables were considered ‘unsuitable’ the grid cell was given a

null classification (disregarded from the analysis).

2.3.3 Identifying potential sites

Once the suitability index was generated the next stage was to examine legal and

environmental constraints and competing uses for potential sites; thus to select sites which

were suitable for macro-algae growth as well as presenting minimal conflicts with other

uses. The possibility of placing macro-algae farms within conservation areas in not

considered an option in this study.

In addition to legal and environmental constraints and competing uses, distance from port

and AIS traffic were also taken into account. Based on the intersection of the environmental

layers with the different constraint layers, 3 potential sites (4 km x 4 km in size) were

chosen.

2.3.4 Detailed comparison of sites

The strengths and weakness of each of the 3 potential sites, in terms of environmental

conditions and conflicting interests, were summarised and compared.

13

3 Results

3.1 Environmental data

Minimum sea surface temperature, SST, (of the 2.5 percentile) ranged from 4.5 oC, around

the Wash, to approximately 7 oC approaching the straits of Dover (Figure 3a), while

maximum SST (of the 97.5 percentile; Figure 3b) varied from approximately 15.5 oC, in the

north of the study area, to 19 oC off mainland Europe.

The depth of the 10% surface irradiance in spring (Figure 3c) ranged between 1 m near the

Thames estuary to more than 6 m at offshore areas. The East Anglian plume (EAP) is clearly

visible as a turbid area stretching out into the southern North Sea (Figure 3c).

Maximum tidal velocity was highest off the straits of Dover (> 2 m s-1) and along the Norfolk

coast between Cromer and Great Yarmouth (between 1 and 2 m s-1), while minimum values

were predicted to occur in the Thames estuary (Figure 3d).

In terms of wave height in autumn, a clear transition is noticeable between the inshore

areas (Humber, Wash and Thames estuaries), characterised by less than 3 m wave height,

and the offshore areas with wave height in excess of 6 m (Figure 4a).

The nutrient layer showed features similar to the result of biogeochemical modelling of the

North Sea given in a previous report (e.g. Figure 6 in Aldridge et al. 2012), with highest

values of dissolved inorganic nitrate in The Wash, in the Essex estuaries and in the Thames

and Humber.

For bathymetry, the majority of the study area falls between 20 and 40 m depth (Figure 4c);

the Thames and Wash estuaries are shallower with average water depth of less than 10 m.

14

a b

c d

Figure 3. Minimum (a) and maximum (b) temperature in °C, depth of the 10% surface

irradiance in m (c), and maximum tidal velocity in m s-1 (d), for the study area.

15

a b

c

Figure 4. Maximum wave height in autumn in m (a), winter dissolved nitrate concentration

in mmol m-3 (b), and bathymetry, m (c), for the study area.

16

3.2 Classified environmental data

The result of the application of optimal, sub-optimal and unsuitable ranges (Table 1) to the

environmental variables (Figures 3 and 4) is given in Figure 5.

Minimal SST is within the optimal range for macro-algae growth in all the study area (Figure

5). Contrarily, only a small proportion of the study area is considered optimal for the

maximum SST for S. latissima, with the majority of the area considered sub-optimal, and the

Thames estuary deemed unsuitable due to maximum SST above 18 °C (Figure 5).

With regards to maximum tidal velocity, a large section north and north-east of the Norfolk

coast is considered optimal as well as areas in the Thames estuary. Most of the remaining of

the study area presents sub-optimal conditions for macro-algae growth, with only a small

section of unsuitable conditions in the Straits of Dover (Figure 5).

Almost the entire East Anglian coastline is characterised by optimal wave height, with north

Norfolk and Thames estuary presenting the largest areas of continuous optimal conditions.

The depth of 10% surface light showed an opposite spatial distribution to wave height, with

unsuitable turbid areas around the coast, particularly in the Thames estuary and along the

Suffolk coast, due to the influence of the EAP (Figure 5). Only exception to this pattern is the

north Norfolk coastline, which present a sub-optimal light climate.

As can be reasonably expected, dissolved nutrient concentration is in the optimal range in

the estuaries of the Wash and Thames, with the remaining part of the East Anglia coast

falling in a sub-optimal range. Moving offshore, nutrient concentration become unsuitable

for macro-algae farming (Figure 5).

In term of bathymetry the majority of the East Anglian coastline is within the optimal range,

with the exception of the shallow areas of the Wash and Thames estuaries which are

classified as unsuitable (Figure 5). The deepest point (Inner Silver Pit; > 60 m depth) was

classified as unsuitable.

In summary, the Thames and Wash estuaries are characterised by ideal conditions in terms

of nutrients, wave height and tidal velocity, however these areas are likely to be too turbid

and shallow for macro-algae farming, as well as potentially too warm (the latest particularly

for the Thames estuary). The area north of the north Norfolk coast is classified either as

optimal or sub-optimal by all the 7 environmental variables (Figure 5).

17

Figure 5. Optimal, sub-optimal and unsuitable conditions for macro-algae growth for each

environmental variable (minimum and maximum temperature, tidal velocity, wave height,

10% light depth, nutrient and bathymetry). The ranges of the environmental variables are

given in Table 1.

18

3.3 Combined layers into suitability index

The classified data layers were combined into the suitability index (Figure 6) as described in

section 2.2.2. No grid cells had a suitability score of 1, indicating that in no areas were all

variables in the optimal range. The highest rated areas (darker brown, Figure 6) are all

located off the north Norfolk coastline and off the Humber estuary.

Figure 6. Suitable areas (optimal and sub-optimal areas combined) for macro-algae farming

off the East Anglian coast, obtained intersecting the environmental variables shown in

Figures 3 and 4. The colour scale highlights the proportion of the environmental variables

considered optimal in the analysis (where 0 is none, and 1 is all variables).

19

3.4 Potential sites identified

In order to identify potential farm sites it was necessary to assess the spatial extent of legal

and environmental constraints and conflicting sea uses (Figure 7). Some of the areas which

show the highest environmental suitability for macro-algae farming coincide with

conservation designations (such as The Wash and North Norfolk Coast SAC and Inner

Dowsing MPA), and existing windfarm sites (Sheringham Shoal Offshore windfarm).

Three potential sites were selected based on the most suitable environmental conditions

while minimizing conflicts with other uses (Figure 7). In particular:

Site 1: is located in a moderately high suitability area, on the north-east of Wells-

next-the-Sea. It borders Sherringham Shoal Offshore windfarm on the west.

Site 2: is the closer to the coast (off Wells-next-the-Sea), to the west of Site 1; it

borders the Wash and North Norfolk Coast SAC to the south and the Inner Dowsing

MPA to the north.

Site 3: is the most northerly site, off the Humber estuary, and almost at the limit of

the study area. It is directly to the west of the deep channel called Inner Silver Pit.

In the sites selection process it was also important to consider the distance from ports

(access constrains; Figure 8) and information on vessel traffic data (Figure 9). In relation to

the latter, the East Anglia coast showed the highest density of vessel traffic, except for the

shallow estuary of the Wash (Figure 9).

20

Figure 7. Environmental and legal constraints and conflicting uses for the study area, with

highlighted the suitable areas and the three potential sites.

21

Figure 8. Distance to ports, expressed as nautical miles (nmi). The three potential sites for

macro-algae farms are highlighted in pink.

22

Figure 9. AIS vessel ping density in the study area. The three potential sites for macro-algae

farms are highlighted in pink. [Includes material © 2014 exactEarth Ltd. and Vesseltracker

GmbH. All Rights Reserved]

23

The main environmental data and constraints for each of the 3 potential sites are

summarised in Table 2. Site 2 is the shallowest site with a mean water depth of 15 m, while

sites 1 and 3 are slightly deeper with approximate depth of 20 m (Table 2). The three sites

have a similar minimum SST (approximately 5 oC), with Site 2 presenting slightly cooler SST

(perhaps related to its proximity to the coast). Site 3 has a maximum SST of 1 oC cooler than

Sites 1 and 2 (Table 2).

All sites are estimated to have a peak tidal velocities of the < 1m s-1 and ranging between 0.7

(Site 2) and 0.97 m s-1 (Site 3). Site 3 is the most exposed to wind generated waves with

significant wave height of approximate 3 m. Site 2 appears to be the most suitable with

wave height < 2 m.

Site 2 is the closest to port (8.3 nmi), being less than half the distance than Site 1 (17.6 nmi)

and 3 (24.9 nmi). Furthermore Site 2 is the only site to have an ‘optimal’ nutrient range,

while the other Sites 1 and 3 have sub-optimal levels.

AIS ping density indicates that Site 2 is in an area of low vessel traffic, Site 1 is in an area of

moderate-high traffic, and Site 3 is in a moderate-low area.

In summary, Site 1 is the deepest site and potentially the least turbid. Site 2 is the least

exposed to waves, and has an optimal level of nutrients during winter; it is also the closest

to port (Wells-next-the-Sea) and had the lowest indicated vessel traffic. However it is also

the most turbid site. Finally, Site 3 has optimal temperature range but it is the most

exposed, with the highest maximum tidal velocity and wave height, as well as being the

furthest from port (Grimsby).

24

Table 2. Summary of the environmental data and constraints at the three potential sites for

macro-algae farming.

Site1 Site2 Site3 Longitude 1.252 0.952 0.622

Latitude 53.113 53.073 53.533

Mean water depth (m) 20.44 15.58 19.11

Minimum SST (°C) 4.9 4.72 5.12

Maximum SST (°C) 16.57 16.88 15.53

Peak Tidal Velocity (m s-1) 0.87 0.7 0.97

Wave height in autumn (m) 2.65 1.67 3.02

10% light depth (m) 3.16 2.36 3.14

Nitrate levels Sub-optimal Optimal Sub-optimal

Distance to port (nmi) 17.55 8.28 24.85

Nearest port Wells-next-the-Sea Wells-next-the-Sea Grimsby

AIS Traffic level Moderate/High Low Low/Moderate

3.5 Qualitative assessment of site selection process

The suitability index was compared to historical observations of Saccharina latissima

provided by The Crown Estate and The Natural History Museum (Figure 10). The

observations have been collected along the shoreline since the 1930s. The main

concentrations of observed presence records are along the northern coast of Norfolk, in the

Blackwater and Colne estuaries in Suffolk, and also along the Kent coast between Margate

and Ramsgate. The observations along the northern coast of Norfolk correspond well with

the output of the suitability analysis, while the observations to the south are not in

agreement with the analysis. This is due to these areas being deemed unsuitable because of

light climate (too turbid) and bathymetry (too shallow); this topic is further addressed in the

discussion (Section 4).

25

Figure 10. In situ observations of kelp (Saccharina latissima) presence along the East Anglia

coast. The three potential sites for macro-algae farming, as well as suitable areas, are also

highlighted in the map.

26

4 Discussion

4.1 Ranges of environmental variables

The optimal, sub-optimal and unsuitable ranges for the different environmental data (Table

1) were selected based on literature research and expert opinion. Considerations used for

determining optimal/sub-optimal/unsuitable ranges are provided in details below.

Temperature

Ranges were defined based on a Bolton and Lüning (1982) study on Saccharina latissima.

The authors observed that the optimal temperature range for growth of S. latissima is

between 10 and 15 °C, while at temperatures of 5 and 20 °C the growth rate is 60-70% and

50-70% of optimal growth rates, respectively. At 0 °C S. latissima is still able to grow but at

20-40% of the optimal growth rate; contrarily after 7 days at 23 °C plants disintegrate

(Bolton and Lüning 1982). As specified in the method (Section 2.1.1), the approach of using

the 95% of the observations for determining ranges was used considering that the effects of

macro-algae exposure to extreme temperatures is more severe when exposure is

prolonged.

Light climate

The absolute lower limit for kelp distribution (Laminaria hyperborea) is set by Lüning and

Dring (1979) at 0.7% of surface light. Saturation irradiance for Laminaria and Saccharina is

usually reached at irradiance < 150 μmol photons m-2 s-1 (100-145 μmol photons m-2 s-1,

Drew 1983; 50-70 μmol photons m-2 s-1, Lüning 1979; 20-100 μmol photons m-2 s-1, Bartsch

et al. 2008); however Han and Kain (1996) observed that the minimum irradiance required

for growth of young sporophytes of L. hyperborea is of just 1 μmol photons m-2 s-1.

The 10% surface light depth was chosen as descriptor of the light climate to make sure that

a portion of the water column fell in an optimal range of irradiance for photosynthetic

activity (not light limited). Kelp can still grow below the 10% irradiance depth but at a slower

rate, which potentially would not be economically viable. A deeper photic zone would give a

kelp farmer more possibilities to manage the exact depth at which the algae are located in

27

order to maximise the yield or the production of high value bio-molecules such as alginate

or carotenes.

Tidal velocity and wave height

The key reference for determining ranges of tidal velocity and wave height was the work by

Buck and Buchholz (2005), who studied drag forces of S. latissima in cultures in the German

Bight. During the study period (in 2002), the authors observed that the S. latissima

sporophytes at an offshore farm withstood maximum current velocity of 1.52 m s-1 and

wave height of 6.46 m. The authors observed that sporophytes which grew in tanks with low

water movement (e.g. simply by air bubbles) were significantly less resistant to dislodgment

and breaking forces, compared to sporophytes which were subjected to relative strong

currents since an early age. In fact it was observed that exposing the developing

sporophytes to strong currents > 1 m s-1 was a necessary pre-requisite for improving

attachment strength of the holdfast, resistance of the stipe to breakage, and for developing

a flat blade with smaller drag (Buck and Buchholz 2005).

In this study, tidal velocity > 2 m s-1 and wave height > 6 m were considered unsuitable for

macro-algae farming, although Buck and Buchholz (2005) suggested that cultivation in

environmental conditions above these thresholds would be still possible, as long as the

algae density on the rope was reduced (presumably to allow larger holdfasts to develop

around the rope). In this study, the unsuitability thresholds were determined on the base

that reduced density algae would provide a smaller yield, which would likely to be not

economically viable.

The probability of catastrophic loss of the farm during winter storm events must also be

factored into the site placement, and for this reason it would be necessary to study the local

wave climate in more details for extremely rare maximum wave height events e.g. using

WaveNet continuous data.

Low current speeds and low or absent waves were considered as sub-optimal conditions

because, as seen in Stephens et al. 2014 (and reference within), water movement around

the kelp plant is important for replenishment of nutrients, reducing self-shading and

presence of epiphytic and grazers. Vigorous water exchange around the algal thalli would be

more important if the farm structure uses a two-dimensional membrane system such as

28

that being trialled by the at_sea project (http://www.atsea-project.eu/). In this case,

nutrient replenishment from the water below the farm would be limited, and the farm sited

so that horizontal exchange would be maximised.

Bathymetry

Based on the study by Radiarta et al. 2011 for cultivation of Japanese kelp, a water depth

between 10 and 30 m was considered optimal for macro-algae farming using hanging-

culture on ropes. If other cultivation techniques are going to be used (e.g. two-dimensional

membrane systems) the optimal water depth could be reconsidered taking into account the

specific engineering requirements of the farm. A bathymetry of more than 50 m was

considered unsuitable due to likely higher operational costs and difficulties in the mooring

system.

Nutrients

As shown by Conolly and Drew (1985) elevated level of nutrient concentration increase the

growth rate of natural kelp populations. However, nutrients uptake by kelp can be affected

by different physical, chemical and biological factors, such as light availability, temperature,

and water movement around plants (Harrison and Hurd 2001). When nutrients are

abundant and their availability exceeds the metabolic requirements, kelp plants exhibit

what has been termed as ‘luxurious uptake’. Under such circumstances, plants continue

taking in nutrients which are stored in the plant tissues (Birkett et al. 1998), in both organic

and inorganic forms.

The maximum uptake rate (Vmax) for nitrate for S. latissima has shown to increase with

nitrate concentration up to 30 μM (Ahn et al. 1998), or with concentrations between 10 and

20 μM, according to Chapman et al. (1978).

Optimal/sub-optimal/unsuitable ranges for nutrient (nitrate) concentration were chosen

based on expert judgement, considering information available in literature of maximum rate

uptake (above), and results from a previous report (Aldridge et al. 2012). Certainly, macro-

algae grow at sub-optimal concentration although likely with a different growth rate

compared to optimal conditions.

29

Constraints and conflicting uses

Potential sites were chosen on the basis that that they would not intersect or overlap with

any other sea use. However, it is conceivable that shared uses may be possible in some

circumstances. For example, following the example of Buck et al. (2004), if an appropriate

co-management strategy is in place, a macro-algae farm could be integrated alongside an

existing windfarm. Also, the prospect of placing a macro-algae farm within an

MPA/SAC/MCZ could be explored with the relevant conservation bodies (Natural England

and JNCC).

AIS vessel traffic

The scale of vessel traffic, including commercial fishing activities by vessels large enough to

be fitted with AIS, used in this study was determined by a basic analysis to be interpreted as

a qualitative guide when exploring potential sites. A more comprehensive analysis would be

needed to consider other aspects such as vessel speed and size. It was assumed that high

vessel traffic has negative implications on selecting potential macro-algae farm sites

however the full implications of placing a farm in high traffic are not known. Furthermore,

the legal and safety implications regarding navigation of vessel traffic around potential

farms were not considered in this analysis.

4.2 Site selection

The GIS-based approach of intersecting relevant layers (environmental data, constraints,

and conflicting uses) was shown to be a useful and flexible tool in selecting suitable sites for

macro-algae farming.

The three sites identified as potential locations for macro-algae farm are representative of

the most suitable areas for cultivation; however they do not represent the only possible

solution, especially if farms with dimensions smaller of 4 km by 4 km are considered. The

size of the farm of 4 km by 4 km was chosen to be consistent with previous projects

commissioned by The Crown Estate (Aldridge et al. 2012; Stephens et al. 2014). Therefore

the 3 sites were chosen on the basis that they could fit these dimensions; a farm with

smaller dimension would increase the number of placement opportunities in suitable areas.

30

Suitable areas within SACs/MPAs or MCZs were excluded from the analysis. Considering that

areas of a high suitability scores occurred in planned or designated conservation areas, the

prospect of placing macro-algae farms within conservation areas should be discussed with

the relevant conservation authorities.

The three sites were selected minimising overlaps with existing uses; however, the presence

of an existing maritime activity does not wholly exclude an area for use as a macro-algae

farm site. In fact co-location of industries is an important part of marine spatial planning

(Gilliland and Laffoley 2008) and can have positive implications (e.g. economical,

maintenance).

To improve the site suitability selection analysis, further access constraints, such as distance

to plant/processing areas on land, as well as engineering constraints (in relation to the

physical structure of the farm) could also be taken into account.

Consideration by The Crown Estate of potential conflicts with other sea users is shown in

Figure 11. This indicates that of the three sites, Site 2 would be the easiest to develop in

having fewer conflicts.

31

Figure 11. Location of the three potential sites in relation to other activities.

32

4.3 Comparison with historical in situ observations

Historical observations from the north Norfolk coast corroborate the outcome of the

suitability analysis. However, the historical observations for Suffolk and Kent coast occurred

in areas which were deemed as not suitable for macro-algae cultivation by the GIS analysis,

because of water depth (too shallow for farming) and light climate (too turbid). The

potential reasons for this discrepancy are likely to be a result of one or more of the

following:

a) temporal discrepancy between environmental variables, used in the analysis, and in situ

observations; the latter were collected between 1930s and 1960s, while the analysis in this

study used modelled and remote sensing data from the last 10 years. The work of Capuzzo

et al. (2014, submitted) showed that underwater light penetration in the southern North

Sea has decreased over the past century. Reductions in the coverage of macro-algae due to

increased turbidity and eutrophication have also been observed in the Baltic Sea (Fleming-

Lehtinen and Laamanen 2012);

b) the depth of the 10% surface light was chosen assuming that a portion of the water

column has sufficient light to support optimal kelp growth. As discussed in section 4.1, this

does not preclude the growth of macro-algae outside these areas, although growth rate are

likely to be slower and/or not economically viable;

c) some of the areas classified as unsuitable had less than 10 m water depth therefore

classified as too shallow; this is concerning the cultivation of the kelp rather than the

presence of the natural population. It is obviously possible for kelp populations to grow in

depth less than 10 m; for S. latissima the natural habitat is the depth range from the low

water mark of spring tides to depths of 20 m. Competition with other kelps usually prevents

S. latissima from exploiting the full extent of its lower depth range.

33

5 Conclusions and recommendations

The key conclusion of this study is that the areas off the north Norfolk coast and off the

Humber estuary were identified to be the most suitable for macro-algae cultivation, in

terms of optimal/sub-optimal environmental conditions for macro-algae growth and

minimum conflict with other uses. Historical observations of Saccharina latissima presence

in the coastal area of north Norfolk support this result. Potential sites for location of farms

with dimensions of 4 km by 4 km were identified:

o Site 1 is located on the north-east of Wells-next-the-Sea; it is the deepest site and

potentially the least turbid.

o Site 2 is the least exposed to waves, and has an optimal level of nutrients during

winter; it is also the closest to port (Wells-next-the-Sea) and had the lowest

indicated vessel traffic and least conflicts. However it is also the most turbid site.

o Site 3 is the most northerly site off the Humber estuary; it has optimal

temperature range. This site is the most exposed with the highest maximum tidal

velocity and wave height, as well as being the furthest from port (Grimsby);

Recommendations arising from this study are:

1) to apply the Combined Kelp Phytoplankton model (CKP), developed during a

previous project (Aldridge et al. 2012), to simulate macro-algae growth, nutrient

uptake and potential effect of macro-algae farms at selected sites off the East Anglia

coast;

2) to run a trial (pilot farm) to ascertain the suitability of the environmental conditions,

as well as potential growth rates, and biochemical composition of the farmed macro-

algae at selected sites;

3) to discuss with relevant conservation authorities the prospect of placing macro-algae

farms within conservation areas (considering that areas of a high suitability occurred

in planned or designated conservation areas);

4) to explore option of co-management/co-location of industries, as integrating macro-

algae farms with windfarms or other aquaculture options could optimise uses of

sites with suitable conditions.

34

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The Crown Estate 16 New Burlington Place London W1S 2HX Tel: 020 7851 5080

www.thecrownestate.co.uk

ISBN: 978-1-906410-61-2