coastal plant communities and sea level rise: is the sediment suitable for seagrass growth?

Coastal plant communities and Coastal plant communities and sea level rise: Is the sediment sea level rise: Is the sediment suitable for seagrass growth?suitable for seagrass growth?

E. Caroline WicksE. Caroline Wicks

January 23, 2006January 23, 2006

SAV WorkgroupSAV Workgroup

www.dnr.state.md.us

T. CarruthersE. Koch

Outline of talk

• Sea level rise

• My research– Hypotheses

– Methods

– Results

• Conclusions– My research

– The big picture

Positive effects of marsh-seagrass interactions

• Transport of organic matter and nutrients between systems (Whiting et al. 1989)

• Marshes reduce eutrophication of shallow waters by filtering out land-based nutrients (Valiela and Cole 2002)

• The effect of linked ecosystems for associated fauna (Irlandi and Crawford 1997)

www.nwrc.usgs.gov www.deq.state.va.us

TM Marsh Index: Healthy, Moderate Deterioration, Severe Deterioration

The ramifications of sea level rise

• Relative sea level rise – Enhanced effects of

extreme meteorological events (flooding)

– Shoreline erosion

• 3 mm yr-1 on Maryland’s Eastern Shore

• 70% of marshes in Chesapeake Bay are degraded (Kearney et al. 2002)

• 31% of Maryland’s coastline (4360 miles) is eroding (State of the Beach 2004)

The impact of sea level rise on seagrasses

• Shifts in distribution and community structure (Short and Neckles 1999)

• Shallow marine sediment erosion leads to seagrass loss (Duarte 2002)

• Seagrasses should be able to colonize newly inundated land, but total coverage should not change (Duarte 2002)

• Mill’s Island, Chincoteague Bay, Maryland– Retreating marsh

shoreline with an eroding dune

– Seagrass bed in subtidal area adjacent to retreating marsh

Study site

www.ian.umces.eduwww.vims.edu/sav

Processes affecting seagrass distribution adjacent to retreating marshes

• Marsh shoreline retreat• Sand from eroding dune

transported along shore• A layered sediment

environment for seagrasses

Old marsh peat

Sand

E. Koch

www.vims.edu/bio/sav

• 80 cm depth contour through seagrass bed• 15 points along transect to sample the

range of sand layer depths• Sediment organic content, seagrass

density, biomass, leaf and root length quantified E. Koch

Field survey at Mill’s Island, Chincoteague Bay

Hypothesis 1: Organic content of sediments adjacent to retreating marshes (i.e. old marsh

peat) is limiting to seagrass growth

Seagrass density decreased with increasing sediment organic content at Mill’s Island

Controlled mesocosm experiment

• 4 seedlings per compartment

• 8 weeks• Quantify biomass,

length and growth rate (Dennison 1990)

Does seagrass growth show a trend with sediment organic content?

0.1%1.2% 4.4%

Seagrass biomass is significantly different between treatments

• One way ANOVA, p < 0.05

• Pairwise comparison using Least Squares Method, p < 0.05

• Sand layer depth measured at 15 points

• Seagrass growth parameters

Old marsh peat

Sand

Hypothesis 2: A thin layer of sand overlaying organic rich sediments adjacent to retreating

marshes allows for seagrass growth

Seagrass density as a function of sand layer depth

Polynomial regression

Controlled laboratory experiment

• 5 treatments• 3 replicates of each,

6 replicates of 0 SLD• 3 seedlings per core• Water change every

week• Ran for 8 weeks• Quantify biomass and

length

Sand layer depth determines root length

Plant morphology may explain conflicting results

• Sediment organic content– Mesocosm experiment shows the sediment organic

content adjacent to retreating marshes is not limiting seagrass distribution or growth parameters

– Field results suggest the opposite trend– Plant morphology

Seagrass morphology in different sediments – How does wave energy

affect the plants?

E. Koch

Summary of processes affecting seagrass growth at Mill’s Island, Chincoteague Bay

Seagrass migration towards land may depend on local factors

Thank you!

CommitteeDr. Evamaria KochDr. Bill Dennison

Dr. Court Stevenson

Computer HelpDave Kimmel

IAN GroupLamere Hennessee, MGS

Tom Fisher Greg Radcliffe

Dave Wilcox, VIMS

Field and Lab HelpBill Severn

Ralph KimesGordy Dawson

Lois LaneJack Seabrease

Angie HengstJames Kampmeyer

Blaise Brown

Friends and FamilyShih-nan Chen Angie Hengst

Erin and Chris MarkinDaidipya Patwa

Jeremy TestaJane Thomas