Date of Award

Spring 2011

Document Type

Legacy Thesis

Degree Name

Master of Science in Coastal Marine and Wetland Studies

Department

Coastal and Marine Systems Science

College

College of Science

First Advisor

Keith R. Walters

Second Advisor

Erin J. Burge

Third Advisor

John J. Hutchens, Jr.

Additional Advisors

Martin Posey

Abstract

Predation on reef-forming bivalves can be important to reef formation and community composition. As a reef resident, mud crabs (Panopeus herbstii) have the potential to increase juvenile oyster (Crassostrea virginica) and mussel (Geukensia demissa) mortality. While mud crabs have the capacity to consume significant numbers of bivalves, mud crab prey preferences have not been studied. Reef surveys were conducted on three reefs within Hog, Murrells, and North Inlets to assess various physical and biological parameters along with mud crab densities along the northern South Carolina coast. Subsequent experiments were set up using mussels in flow-through sea water tanks at the Baruch Marine Field Laboratory in Georgetown, SC and loose seed oysters in closed-system mesocosms at Coastal Carolina University. Each experiment used treatments of various sized mud crabs, which included small (10-18 mm), medium (18-27 mm), and large (27-40 mm) sized mud crabs. Mussel experiments in flow-through sea water tanks investigated differences in male and female crab prey consumption, crab mussel size preference, and crab competition. Experiments in closed-system mesocosms investigated crab prey preferences using mussels and oysters, crab prey consumption using attached and loose oysters, and crab oyster consumption using various depths of water coverage. There was no difference between feeding rates of similar sized male and female mud crabs. All sizes of mud crabs consistently fed on smaller (10-15 mm) than larger (15-25 mm) sized mussels. There was no evidence of consistent mud crab competition among various size combinations. Mussels had a greater ash free dry mass (AFDM) than oysters. Crabs did not exhibit a preference between mussels and oysters. However, when consuming similar numbers of mussels and oysters, crabs consumed a greater amount of AFDM from mussels. Crabs consumed a significantly greater number of loose versus attached oysters, and also consumed a greater number of oysters in submerged versus exposed treatments. Based on parameters from reef surveys and experiments, maximal crab consumption rates were calculated to be applied to oysters and mussels in the field. A medium (18-27 mm) sized crab could consume 28% of mussels/m2 per day or 1.8% of attached oysters/m2 per day. Actual consumption rates in the field are probably much lower due to refuge availability and the presence of other predators; however these numbers offer a maximum feeding rate, which indicates that mud crabs can have a major impact on juvenile mussels and oysters.

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