Oyster Abundance in Apalachicola Bay, Florida in Relation to Biotic Associations Influenced by Salinity and Other Factors

Abstract

From June 1955 through May 1957, stations o n three oyster reefs were sampled qwntitatiuely at intervals and all oysters and associated macroscopic organisms were recorded per unit area. Station I was a priuately leased “natllral” reef, consisting of higher places exposed at low water, with a salinity range of 22.7-36.6 o/oo and was fairly productiue. Station 11, depth ca. t w o meters, was t h e least saline, range 1.2-29.3 o/oo, and was considered uery productiue for natural reef. Station I l l , depth one meter, salinity range 7.5-35.7 o/oo, wus depleted although there was an abundant spatfall. Depth and bottom types as well as salinity were found to delimir certain species of animals. Analysis of past records showed that t he bay had formerly been less saline; there was a n extended drought in the watershed before and during the inuestigation. As a result several species o f animals less euryhaline than oysters became established o n some o f t he reefs. At Station I l l , t w o serious oyster enemies, Thais haemastoma Say and Menippe mercenaria Conrad were abzrndant. A field experiment at this station during the second year pointed t o these t w o enemies as the main cause of t h e depletion of t he reef. Near the end of t he inuestigation rainfall became more Beady normal and the lowest salinities were recorded at this time. T h e reduction in salinity, especially at Station 111, eliminated many of t he less euryhaline species, including drills and stone crabs, and t h e reef later regained its former productiuity. 1 Contribution No. 213, Oceanographic Institute, Florida State University. This study was supported by a contract with the U. S. Fish and Wildlife Service through Saltonstall-Kennedy Funds.