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Habitat Preferences and Predation of the Softshell Clam, Mya arenaria, in the Lower Chesapeake Bay

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Author: Bovery, Caitlin Mary
Advisor: Swaddle, John P.
Committee Members: Seitz, Rochelle; Chambers, Randolph M.; Allen, Jonathan D.
Issued Date: 2010-05-14
Subjects: Marine science
URI: http://hdl.handle.net/10288/2024
Description: Soft-shell clams (Mya arenaria), once abundant, are currently in decline in the Chesapeake Bay, nearing disappearance from some areas in the lower Chesapeake Bay. Proposed explanations for these regional declines include residual effects of Tropical Storm Agnes (1972) and intense pressures from predators. This study was designed to examine the potential for restoring declining populations of M. arenaria in the Lynnhaven river system through transplanting juvenile clams. We used Manipulative field experiments to determine the survival and growth of transplanted juvenile M. arenaria in replicate plots at two locations: Broad Bay and Pleasure House Creek. We also utilized various substrate types (sand, gravel, oyster shell) and predator exclusion techniques (caged vs. open plots) to examine changes in M. arenaria survival and growth. At the conclusion of the study, survival of transplanted clams and abundance of ambient bivalves were both significantly higher in caged plots as compared to open plots, indicating a significant contribution of predation to clam mortality. High mortality rates were observed in all caged and open plots, suggesting that environmental conditions also contributed to mortality. In addition, the most abundant ambient bivalves were Aligena elevata, a bivalve that lives commensally with a polychaete, and Tagelus plebeius, a deep-dwelling bivalve. These two species appear to have developed mechanisms to survive in the face of predation pressures and were the species most suited to the Lynnhaven River System. Substrate type did not affect transplanted clam survival, though diversity of ambient clams was highest in gravel habitats. The results of this study indicate that future restoration efforts for M. arenaria in the Lynnhaven river system are likely to be most successful at establishing a resident population of M. arenaria if deeper, cooler-water locations are used and significant predator-exclusion cages or substantial amounts of structural substrate are used.
Degree: Bachelors of Science in Biology

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