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

From June 1955 through May 1957, stations on three oyster reefs were sampled quantitatively at intervals and all oysters and associated macroscopic organisms were recorded per unit area. Station I was a privately leased “natural” reef, consisting of higher places exposed at low water, with a salinity range of 22.7-36.6 o/oo and was fairly productive. Station II, depth ca. two meters, was the least saline, range 1.2-29.3 o/oo, and was considered very productive for natural reef. Station III, depth one meter, salinity range 7.5-35.7 o/oo, was depleted although there was an abundant spatfall. Depth and bottom types as well as salinity were found to delimit certain species of animals. Analysis of past records showed that the bay had formerly been less saline; there was an extended drought in the watershed before and during the investigation. As a result several species of animals less euryhaline than oysters became established on some of the reefs. At Station III, two serious oyster enemies, Thais haemastoma Say and Menippe mercenaria Conrad were abundant. A field experiment at this station during the second year pointed to these two enemies as the main cause of the depletion of the reef. Near the end of the investigation rainfall became more nearly normal and the lowest salinities were recorded at this time. The reduction in salinity, especially at Station III, eliminated many of the less euryhaline species, including drills and stone crabs, and the reef later regained its former productivity