Biotic potential and environmental resistance in the American oyster ( Crassostrea virginica) in Long Island Sound

Abstract

The American oyster ( Crassostrea virginica) in Long Island Sound was studied throughout its life span on commercial beds by conducting SCUBA surveys and supporting laboratory tests from 1966–1972. The oyster had a biotic potential of a magnitude large enough to cover the entire bottom of the Sound within a few years, given optimum environmental conditions. The limiting factors were mainly: low temperatures, a lack of clean shell substratum on which oyster larvae could set, and about 20 causes of mortality in sedentary oysters, the most substantial of which were: (1) predation by starfish ( Asterias forbesi), oyster drills ( Eupleura caudata and Urosalpinx cinerea) and crabs ( Cancer irroratus and Neopanope sayi); (2) competition by slipper-shells ( Crepidula fornicata and Crepidula plana) and other animals on shells; (3) suffocation by silt and (4) shell fracture during transplanting by oyster growers. Oyster mortalities occurred mostly from spring to fall and were negligible during winter. The mortalities were area-specific within beds, bed-specific and much higher in spat than in 1, 2 and 3-year-old oysters. The survival of oysters from setting of spat throughout their life span on cultured beds was estimated to be 2–5%. Few oysters could survive in the Sound without bed culture. During 1966 and continuing afterwards, the growers applied improved cultural methods and new technologies to remove a number of limiting factors from the beds, and this resulted in an oyster “abundance and production takeoff”.