how global warming and climate change may be accelerating...

How global warming and climate change How global warming and climate change may be accelerating losses of may be accelerating losses of Chesapeake BayChesapeake Bay seagrassesseagrasses..

Dr. Ken Moore

The Virginia Institute of Marine ScienceSchool of Marine Science

College of William and MaryGloucester Point, VA USA

What Are Underwater Grasses?• Rooted, vascular plants

– does not include marsh grasses or algae

• Completely submerged• Have flowers and seeds• 17 common species in

Chesapeake Bay• Grow in fresh and salt

shallow tidal waters• Only one true seagrass

species in Chesapeake Bay (eelgrass)

Underwater grasses of Chesapeake Bay

Only “True”Seagrass

Underwater grass communities are important in Chesapeake Bay

• Food for waterfowl

• Increase water clarity

• Habitat for fish and crabs

http://rds.yahoo.com/S=96062883/K=duck+photo/v=2/SID=e/l=IVI/SIG=11t091ma1/*-http%3A//www.all-creatures.org/works/images/w-bid-duck.jpg

Underwater grass communities are widely distributed in Chesapeake Bay

ZosteraZostera marinamarina‘‘eelgrasseelgrass’’

York RiverYork River

Ruppia maritimaRuppia maritima‘‘widgeongrasswidgeongrass’’

St MarySt Mary’’s Rivers River

http://www.vims.edu/bio/sav/2004_SAV_Photo_Gallery/St._Marys_2.jpg

Underwater grass communities are by distributed salinity

Chesapeake Bay Underwater Chesapeake Bay Underwater Grass CommunitiesGrass Communities

Moore, Wilcox,Moore, Wilcox, OrthOrth (2000) Estuaries 23:115(2000) Estuaries 23:115--227227

FreshwaterFreshwater PotamogetonPotamogeton

RuppiaRuppia ZosteraZostera

ZOSTERA ZOSTERA Community Zostera marina*Ruppia maritima

RUPPIA RUPPIA Community Ruppia maritima*Potamogeton perfoliatusPotamogeton pectinatusZannichellia palustris

POTAMOGETONPOTAMOGETON Community Potamogeton perfoliatus*Potamogeton pectinatus*Elodea canadensisPotamogeton crispus

FRESHWATERFRESHWATER Community Myriophyllum spicatum*Hydrilla verticillata*Vallisneria americana*Ceratophyllum demersumHeteranthera dubiaNajas minorElodea canadensisNajas guadalupensisPotamogeton crispusNajas gracillimaPotamogeton pusillus

*Dominant Species

CHESAPEAKE BAY UNDERWATER GRASS CHESAPEAKE BAY UNDERWATER GRASS COMMUNITIESCOMMUNITIES

Saltwater

Freshwater

There are very few underwater grass species

TERRESTRIAL250,000 + SPECIES

FRESHWATERSUBMERSED

400-500 SPECIES

SEAGRASS55-60 SPECIES

FRESHWATER WETLAND?? SPECIES

Our only seagrass

Zostera marina (eelgrass)

•Temperate coastal distribution

•Monoecious, Sub-surface pollination (threadlike pollen)

•Sexual reproduction through seeds

•Asexual reproduction through rhizomes

•High salinity tolerance (10-40)

Chesapeake Bay Eelgrass Meadow Landscape

Underwater grasses have

declined in the Chesapeake Bay over the past 60

years.

Less than 50% present today compared to

1950s

Eelgrass populations have also declined

Pre 1930s 1960s 2000

• Pre-1630 Forested Watershed; < 1% land cleared• 1630-1720 Initial European settlement; <20% land

cleared• 1720-1880 Developing Agriculture; 20-40% land

clearance• 1880-1930s Intensive Agriculture 60-80% land

clearance, mechanization, deep plowing, fertilization

• 1930-1950s Farm abandonment, re-forestation, 40% land clearance, initial urban growth, storms

• 1950s-Present Urban Growth(Tropical Storm Agnes 1972 and others)

Chesapeake Bay Historical Land UseChesapeake Bay Historical Land Use

Brush and Hilgartner 2000

Recent Decreases in York River Eelgrass Bed Abundance and Density

2004 Seagrass

1996 2006

Loss of eelgrass in last 10 years is problematicGoodwin Island – York River

Effects of Climate Change on Chespeake BaySeagrasses and Other Underwater Grasses

• Atmospheric Changes– Rainfall Patterns– Increase Nutrient and Sediment Inputs (100% loading increase for C.

Bay)– Frequency/Intensity of storms

• Sea Level Rise– Salinity Changes– Increases in Water Depth, Water Motion and Tidal Circulation– Increased Shoreline Erosion

• Temperature Rise– Physiology, growth, reproduction

A variety of components reflect or absorb sunlight in seawater

Sunlight

Algae

Sediment

Color

Seagrass

Epiphytes

Light Intensity

Dep

th

SeagrassSeagrass responsive to light responsive to light reductionsreductions

Healthy seagrass

Physiological responses•Amino acids

•Chl a/b

•δ13C

Impacted seagrass

Seagrassloss

Morphological responses•Biomass•Shoot density•canopy height•Root/shoot

Period of light deprivation

The greater the underwater

light…

The deeper the underwater grass growth

and

The greater the abundance

2m

1m

0m Mid Estuary

Current Distribution Historic Extent

2m

1m

0m Lower Estuary


2m

1m

0m


Upper Estuary

York River current and historical

eelgrass depth

distribution

Reduced light has been a

factor!

Cerco and Moore 2001

Restoration of SAV to 1 m

MLW depths will initially require reduction in

suspended solids concentrations

Langland and Hainly 1997

Full storage of sediment inFull storage of sediment in ConowingoConowingo Dam Reservoir in Dam Reservoir in next 15next 15--20 years20 years

(Annual average sediment inputs will increase 3(Annual average sediment inputs will increase 3--fold)fold)

Scour during storm events will increase estuarine sedimentation.

(16x annual sediment inputs during one 1996 winter flood)

Image provided by Kawartha Fisheries Association

Excessive Nutrients Promote Excessive Growth of Epiphytes

Impacts of storms onseagrasscan be

significant

AIR AND WATER IN MOTION

Due to the higher density of water (998.2 kg m-3 freshwater)

than air (1.2 kg m-3),

the force exerted by the same velocity on an organism is 827

times stronger in the water than in the air.

But, in highly wave exposed areas,seagrasses are limited to protected

areas

Dan et al. 1998

Japan, Zostera marina, 2 m waves

Chesapeake Bay 1 m waves

Scour and deposition lasting for weeks after storms can result in landscape

scale changes to seagrass beds

Deposition ScourPost Storm SurfacePost Storm Surface

10 meters

Post Storm SurfacePost Storm Surface

The effects of tropical storms observed in eelgrass beds in lower Chesapeake Bay

York River – Goodwin IslandsJune 2004

York River – Goodwin Islands

October 2003

Salinity changes can modify underwater grass distribution and abundance

Chesapeake Bay Underwater Chesapeake Bay Underwater Grass CommunitiesGrass Communities

Moore, Wilcox,Moore, Wilcox, OrthOrth (2000) Estuaries 23:115(2000) Estuaries 23:115--227227

FreshwaterFreshwater PotamogetonPotamogeton

RuppiaRuppia ZosteraZostera

Waves appear to affect the minimum depth of distribution of seagrasses and sealevel rise

can restrict shallow water habitat.

Shoreline erosion can create chronic turbidity for local

waters.

Global distribution of eelgrass (Zostera marina)

Eelgrass near southern limits of range on Atlantic Coast of US

Reprinted from Moore et al. 1997

Light requirements of eelgrass increase with increasing temperatures

Investigate if temperature or some other factor is affecting Chesapeake Bay Seagrass?

1. Quantify the patterns of inter-annual variability and spatial distribution ofseagrass in areas of the lower Chesapeake Bay.

2. Compare the patterns of long-term change in these areas.

3. Relate these patterns to environmental and water quality conditions.

Monitoring Sites

GI 1

GI 3

GI 2

GP 1

GP 2

GP 3

Gloucester Point

Goodwin Island

Fixed continuous WQ monitoring stations:

DO, Phytoplankton, Turbidity, Salinity, pH, Temp

Bi-weekly WQ sampling:

Phytoplankton, Water Column Nutrients, Suspended Sediments, Underwater Light

Seagrass Sampling Methods• Monthly Sampling• Measurements made every 10 m

Ring is placed in densest patch of vegetation within the square

PVC square (0.25m-2

diameter) tossed 3 times every 10 m

York River

Goodwin Is.

Goodwin Island

Gloucester Gloucester PointPoint

Distance (m)0 20 40 60 80 100

Dep

th (c

m M

LLW

)

-160

-140

-120

-100

-80

-60

-40

-20

0 Gloucester Point

Distance (m)

100 300 500 7000 200 400 600

Dep

th (c

m M

LLW

)

-100

-80

-60

-40

-20

0

York River

Bottom Topography

100 300 500 7000 200 400 6000

20

40

60

80

100

100 300 500 7000 200 400 600

Goodwin Island Eelgrass Cover

Distance (m)

0 100 200 300 400 500 600 700

100 300 500 7000 200 400 6000

20

40

60

80

100

100 300 500 7000 200 400 600 100 300 500 7000 200 400 600

Per

cent

Cov

er

May 2004 July 2004 Oct 2004

Per

cent

Cov

er

April 2005 July 2005 Oct 2005

Goodwin Island Eelgrass Cover

100 300 500 7000 200 400 6000

20

40

60

80

100

100 300 500 7000 200 400 600 100 300 500 7000 200 400 600

April 2006 May 2006 July 2006

Per

cent

Cov

er

Distance (m)

Re-growth largely from seedlings

Goodwin Island Eelgrass Bed Mean Percent Cover

Date (mm/yy)01/04 07/04 01/05 07/05 01/06 07/06 01/07 0

20

40

60

80

100Pe

rcen

t Cov

er

0 20 40 60 80 1000

20

40

60

80

100

0 20 40 60 80 100 0 20 40 60 80 100

0 20 40 60 80 1000

20

40

60

80

100

0 20 40 60 80 100 0 20 40 60 80 100

May 2004 June 2004 September 2004

April 2005 July 2005 October 2005

Gloucester Point Eelgrass CoverP

erce

nt C

over

Distance (m)

0 20 40 60 80 1000

20

40

60

80

100

0 20 40 60 80 100 10 30 50 700 20 40 60 80

April 2006 May 2006 July 2006

Per

cent

Cov

er

Distance (m)

Gloucester Point Eelgrass Cover

Very few seedlings found

01/04 07/04 01/05 07/05 01/06 07/06 01/07 0

20

40

60

80

100

Perc

ent C

over

Date

Gloucester Point Eelgrass Bed Mean Percent Cover

Is Turbidity a Factor?

Gloucester Point

Date (month)Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan

Turb

idity

(NTU

)0

20

40

60

80

100

120

140

20042005

Goodwin Island

Date (month)Feb Mar Apr Jun Jul Aug Oct Nov Dec Jan May Sep Jan

Turb

idity

(NTU

)

0

10

20

30

40

50

60200420051997-2003

Turbidity (NTU)

5 15 25 350 10 20 30

Perc

ent T

ime

0

2

4

6

8

10

12

14

16

18

20

Goodwin Island 2004Goodwin Island 2005Gloucester Point 2004Gloucester Point 2005

Turbidity Frequency Distribution for Goodwin Island and Gloucester Point

2004-2005

Sources of oxygen for seagrass metabolismLight – photosynthesis and water column

Dark – water column only


Dis

solv

ed O

xyge

n (m

g l-1

)0

2

4

6

8

10

12

14

16

20042005

Date (month)Jan Feb Mar May Jun Jul Sep Oct Nov Jan Dec Apr Aug Dec

Dis

solv

ed O

xyge

n (m

g l-1

)

0

2

4

6

8

10

12

14

16

1997-200320042005

Goodwin Island Gloucester Point

Water Column Dissolved Oxygen

Dissolved Oxygen (mg L-1)

0 2 4 6 8 10 12 14

Perc

ent T

ime

0

2

4

6

8

10

12

14

16 Goodwind Island 2004Goodwin Island 2005Gloucester Point 2004Gloucester Point 2005

Water Column Dissolved Oxygen Frequency Distribution for Goodwin Island and Gloucester

Point July and August 2004-2005

Are High Water Temperatures a Problem?

Goodwin Island

Date (month)Feb Mar Apr Jun Jul Aug Oct Nov Dec Jan May Sep Jan

Tem

pera

ture

(C)

0

5

10

15

20

25

30

35

200420051997-2003

Gloucester Point


Tem

pera

ture

(C)

0

5

10

15

20

25

30

35

20042005

Temperature (C)

20 22 24 26 28 30 32 34

Perc

ent T

ime

0

10

20

30

40GI 2004 GP 2004 GI 2005 GP 2005

Water Temp Frequency Distribution for Goodwin Island and Gloucester Point 2004-2005

H co

mp (h

ours

)

0

12

34

56

78

910

1112

Jan Jun De c

Curre ntly Ve g e tatedHis to ric ally Ve g etate d

HOURS PER DAY ABOVE SAV LIGHT COMPENSATION IS VERY IMPORTANT

Light below compensation for 20 days

Summary• The remaining eelgrass beds have been experiencing

increasing frequency of summertime diebacks in shallow and deep regions.

• Global warming and climate change can affect Chesapeake Bay eelgrass survival through multiple ways:– Elevated temperatures can stress growth – Increased frequency and intensity of storms

• Given the long term effects of increases in temperature and turbidity due to global warming and climate change are problematic for continued success of eelgrass populations in this system ….

Thanks!

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