Occurrence of Toxic Bivalve Molluscs during a Gymnodinium breve “Red Tide”

Abstract

Abstract Extensive fish mortality has been associated with Gymnodinium breve “red tides” along the west coast of Florida. Toxicological evidence has strongly incriminated G. breve as being the primary source of two toxic components detected in oysters and clams exposed to increased numbers of G. breve. From August to November 1967, G. breve “red tide” conditions were reported from the mouth of Tampa Bay to Redfish Pass, south of Charlotte Harbor on the west coast of Florida. The present study examines the relationship of increased numbers of G. breve to the occurrence and distribution of toxic oysters and clams. The most severe G. breve “red tide” conditions occurred during the first day of sampling. G. breve cell counts averaged 1500–2400 organisms/ml in the offshore waters, 300 organisms/ml in the surf zone, and 820 organisms/ml in Venice Inlet. Water collected offshore and from the head of the Inlet contained an ether-soluble substance that was toxic to mice. At this time a large number of dead fishes ...