Growth and Physiology of Eastern and Suminoe Oysters and the Implications of Increased Habitat Complexity for Associated Oyster Reef Fauna

The introduction of a non-native oyster species (Crassostrea ariakensis) into Chesapeake Bay has been proposed as a way to help restore the oyster fishery and enhance the ecological services historically provided by eastern (Crassostrea virginica) oysters. A comparison of growth, mortality, and physiology between diploid C. ariakensis (Oregon strain) and diploid C. virginica was undertaken in quarantined mesocosms simulating mesohaline Chesapeake Bay. Growth of C. ariakensis was greatest during the late winter and early spring periods, with oyster condition substantially reduced during the summer due to low clearance rates and elevated respiration rates. Stunted growth and high mortality characterized the C. virginica treatment, although the reasons for this are unknown. Additional quarantined laboratory studies, conducted in Florida for both oyster species in conditions simulating a subtropical estuary examined the potential of C. ariakensis to expand southwards. While growth of C. ariakensis was comparable to that of C. virginica, mortality of C. ariakensis reached 100% by the end of the study, but remained relatively low for C. virginica. Physiological studies under quarantined temperate euhaline conditions (Wachapreague, Virginia) confirmed that C. ariakensis is physiologically intolerant to warmer water (> 20ºC) because of low clearance rates. Oysters create reefs that provide refuge for prey species, and enhanced foraging opportunities for predatory fish species. Predator-prey interactions between organisms found on oyster reefs, such as grass shrimp (Palaemontes pugio), white perch (Morone americana), and striped bass (Morone saxatilis) were conducted on habitats of varying complexity. Habitats consisted of flat sand, and medium and high complexity structures constructed in mesocosms from PVC pipe. As structural complexity increased so did the attraction of grass shrimp and white perch to structure regardless of the provision of food resources or presence of striped bass. The attraction of grass shrimp to structure decreased when high densities of conspecifics were present. The presence of prey and/or predators enhanced white perch utilization of structure and increased complexity decreased their swimming and shoaling activity. Habitat complexity and the threat of predation interact to alter grass shrimp and white perch behavior under intermediate levels of structural complexity