This study examined the population densities of purple marsh crabs and cordgrass in three sites within South Carolina's ACE Basin estuary. Population surveys found varying densities of purple marsh crabs (6.67-25 burrows/m2) and cordgrass (219-270 stalks/m2) across sites. A correlational analysis showed a weak negative relationship between crab and cordgrass populations. Compared to an unhealthy marsh in Cape Cod, the ACE Basin sites showed equally healthy crab and cordgrass densities, suggesting crab overpopulation is not negatively impacting cordgrass there as was seen in Cape Cod. The study aims to establish a baseline of these populations for future monitoring.

1. Purple Marsh Crab and Cordgrass
Population Densities within South
Carolina’s ACE Basin
Alejandra Luna, Ramsey Millison, & Tara Poyer

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

3. Salt Marsh
 Are transitional areas located
along intertidal zones of
estuaries (Wenner, 2010).
 Serve as shoreline erosion
prevention.

4. 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

5. Ecosystem Population Relationships
Secondary
Consumer
Primary
Consumer
Primary
ProducerBlue Crab
Purple Marsh Crab
Cordgrass

6. 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

7. 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

8. 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.

9. Survey Sites in the A.C.E. Basin

11. Population Surveys
 Burrow Counts
(burrows >19mm)
Excavation Sizes
Botany Bay A- 6.67m x 0.7m
Botany Bay B- 2.05m x 0.7m
Ashepoo C- 3.09m x 0.7m
Path
HighTide
 Excavation
(all crabs collected for analysis)
50m
0.5m2

12. Population Surveys
 Burrow Counts
(burrows/m2)
.5m2
Path
HighTide
 Excavation
 Cordgrass counts
(stalks/m2)
50m
0.5m2
0.5m2

13. Results: Correlative Analysis
y = -3.2859x + 219.39
R = -0.336
0
50
100
150
200
250
300
350
0 5 10 15 20 25 30 35 40 45
Cordgrass(stalks/m2)
Purple Marsh Crab (burrows/m2)
Botany Bay A Botany Bay B Ashepoo

14. Population Density Comparisons Between South
Carolina ACE Basin and Cape Cod Massachusetts
0
50
100
150
200
250
300
Ashepoo Botany Bay A Botany Bay B
Stalks/m2
0
5
10
15
20
25
Ashepoo Botany Bay A Botany Bay B
Burrows/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)

15. 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
x̅ = 11.8 SD = 3.54
x̅ = 13.1 SD = 1.48
x̅ = 14.8 SD = 3.97
NumberofPurpleMarshCrabs

16. 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)

17. Salt Marsh Mud Crab Atlantic Mud Crab
Squareback Marsh Crab
Blue Crab
Purple Marsh Crab
Cordgrass Periwinkle Snail

18. 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

19. 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.