Purple Marsh Crab and Cordgrass Population Densities within South

Carolina’s ACE Basin

Alejandra Luna, Ramsey Millison, & Tara Poyer

Estuaries

“Provide more services per unit area than any other ecosystem worldwide” (Gedan K. B. et al. 2011)

Salt Marsh

Are transitional areas located along intertidal zones of estuaries (Wenner, 2010).

Serve as shoreline erosion prevention.

Salt Marsh Die-Off in Cape Cod, Massachusetts

Cordgrass die off on seaward edge of salt marsh Area critical to marsh

development and maintenance. Decreasing barrier capabilities

Gedan K. B. et al. 2011

Gedan K. B. et al. 2009

Ecosystem Population Relationships

Secondary Consumer

Primary Consumer

Primary Producer Blue Crab

Purple Marsh Crab

Cordgrass

Cordgrass Die Off Due to Purple Marsh Crab

Found that all die-off areas had over 100 crab burrows/m2

Speculated overpopulation is due to overfishing of predators of purple marsh crab.

(Holdredge et al. 2008)(Smith et al. 2013)

= die-off marsh = healthy marsh

110

25

Purpose of the Study

1. Establish baseline populations for both cordgrass and purple marsh crab in relatively unfished areas.

2. Characterize population relationships between cordgrass and purple marsh crab.

3. Assess populations of other crab species present.

ACE Basin

Our Study

QUESTION: What are the population characteristics of purple marsh crab and cordgrass? How do they compare to those studied in Cape Cod,

Massachusetts? HYPOTHESIS: As the population of purple marsh crab

changes, the population of cordgrass will change. PREDICTION: As the population of purple marsh crab

increases the population of cordgrass will decrease.

Survey Sites in the A.C.E. Basin

Population Surveys

Burrow Counts (burrows >19mm)

Excavation SizesBotany Bay A- 6.67m x 0.7mBotany Bay B- 2.05m x 0.7mAshepoo C- 3.09m x 0.7m

Path High Tide

Excavation(all crabs collected for analysis)

50m

0.5m2

Population Surveys

Burrow Counts (burrows/m2)

.5m2

Path High Tide

Excavation

Cordgrass counts (stalks/m2)

50m

0.5m2

0.5m2

Results: Correlative Analysis

0 5 10 15 20 25 30 35 40 450

50

100

150

200

250

300

350

f(x) = − 3.28588235294117 x + 219.392941176471R² = 0.113144527272696

Botany Bay A Botany Bay B Ashepoo

Purple Marsh Crab (burrows/m2)

Cord

gras

s (st

alks

/m2)

Population Density Comparisons Between South Carolina ACE Basin and Cape Cod Massachusetts

Ashepoo Botany Bay A Botany Bay B0

50

100

150

200

250

Stal

ks/m

2

Ashepoo Botany Bay A Botany Bay B0

5

10

15

20

25

Burr

ows/

m2

ACE Basin

‘Unhealthy’ Area

Cape Cod

‘Healthy’ Area

Cordgrass

Purple Marsh Crab

270 stalks/m2 0 stalks/m2

25 burrows/m2 110 burrows/m2

(Holdredge et al. 2008)

Botany Bay A

Botany Bay B

Ashepoo

male= = female=

Results: Purple Marsh Crab Size/Sex Distribution

male= 1 female=18

male= 6 female= 3

male= 18 female= 22

xP = 11.8 SD = 3.54

xP = 13.1 SD = 1.48

xP = 14.8 SD = 3.97Num

ber o

f Pur

ple

Mar

sh C

rabs

Results: Community Interactions

Salt Marsh Mud Crab (Panopeus obesus)

Atlantic Mud Crab (Panopeus herbstii)

Squareback Marsh Crab (Armaces cinereum)

Botany Bay

A n=45

Botany Bay B

n=44

Ashepoo n=72

Diet Predators

Squareback marsh 11.11% 75.00 % 27.78% Cordgrass,

leaves, aphids Birds, mammals, larger

crabs

Atlantic Mud Crab 6.67% 0 2.78% Periwinkle

Snails Blue Crab (C. sapidus)

Salt Marsh Mud 17.78% 2.27 % 0 Periwinkle

Snails Blue Crab (C. sapidus)

Purple Marsh Crab 64.44% 22.73% 69.44% Cordgrass Blue Crab (C. sapidus)

Salt Marsh Mud Crab Atlantic Mud Crab

Squareback Marsh Crab

Blue Crab

Purple Marsh Crab

Cordgrass Periwinkle Snail

Conclusions

Purple marsh crab and cordgrass populations are equally healthy in comparison to the healthy salt marshes of Cape Cod.

Purple marsh crab populations appear to affect cordgrass populations, however more populations assessments are needed throughout the ACE basin

Acknowledgements

DePaul University Department of Biological Sciences for funding this research.

Special thanks to South Carolina’s Department of Natural Resources for allowing us to work in the salt marshes and providing room and board during our research.