Eastern oysters offer no pearl, but they might be in peril: understanding how lethal and non lethal predator effects influence oyster distribution and reef community




Johnson, Keith


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The purpose of this dissertation research was to investigate how predation affects oyster distribution and reef community structure by examining: 1) non lethal predation effects on bivalves by size of prey; 2) the lethal and non lethal effects that influence survival and resource allocation in oysters; 3) predation affects distribution patterns of oysters; 4) top-down forces and seasonal effects on oyster reef community structure. Although Eastern oysters, Crassostrea virginica, are ecologically and economically important, oyster populations are declining in many areas and have decreased 85% worldwide. Like many communities, predation or top-down forces can have significant effects on the structure and function of oyster reef communities. The purpose of this study was to ascertain how oyster recruitment, survival, growth and distribution as well as oyster reef community structure were influenced by lethal and non lethal effects of predators. Results from a series of manipulative field experiments indicate that predators have significant effects on oyster reef community structure and oyster recruitment, but, these effects are significantly more important in the fall than spring. Oyster recruitment and spat survival is strongly affected by the abundance of intermediate consumers, most notably the Atlantic mud crab (Panopeus herbstii). In the absence of higher order predators including blue crabs (Callinectes sapidus) and red drum (Scianops ocellatus), mud crabs increased in number and preyed more heavily on newly settled oysters. Mud crabs also caused oysters to change their resource allocation to more shell and less tissue at a cost of lowering fecundity. Finally, oysters are limited to intertidal habitats in Corpus Christi Bay, and these results indicate that oysters are restricted to intertidal habitats by predators. This study elucidates how predators have significant lethal and non lethal effects on oysters and their associated fauna and that top-down forces should be considered when developing oyster reef conservation, management, and restoration efforts.


A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Coastal Marine Systems Science


Crassostrea virginica, oyster reef community, mud crab, top down forces, lethal and non lethal effects, blue crabs, red drum



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