Intraspecific life history variation in the southern oyster drill, Stramonita haemastoma: Patterns and causes

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Along the Louisiana coast of the Gulf of Mexico, the southern oyster drill, Stramonita haemastoma (Gray), reached peak densities at an exposed, coastal location, with lower but more constant densities in an estuarine oyster reef. Average oyster drill size in field samples was largest at the estuarine, intertidal reef and smallest at the exposed location. Caged oyster drills grew more rapidly and were more fecund at the subtidal, estuarine oyster reef than at the exposed location, resulting in higher biomass and production estimates. Life histories thus changed from slower growth, and delayed and semelparous reproduction at the exposed location to rapid growth, and earlier and iteroparous reproduction at the subtidal, estuarine oyster reef. When oysters were added to cages at the exposed location (where they are rare), oyster drill growth and reproductive rates increased dramatically. Trapping revealed no obvious differences in the abundances of crab predators between the estuarine and exposed site, nor were there any differences in gastropod shell thickness (e.g., vulnerability to predators). We conclude that the availability of profitable prey like oysters plays a greater role in explaining oyster drill life history variation than predation risk, and that wave exposure has only indirect effects, by limiting the availability of oysters or forcing oyster drills to feed on smaller prey.

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Journal of Shellfish Research

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