MORTALITY OF THE VEINED RAPA WHELK, RAPANA VENOSA, IN RELATION TO A BLOOM OF ALEXANDRIUM MONILATUM IN THE YORK RIVER, UNITED STATES

Veined rapa whelks (Rapana venosa), carnivorous marine gastropods experienced significant mortality during an Alexandrium monilatum bloom in the lower York River, VA in September 2007. Rapa whelks stopped feeding as dissolved oxygen and chlorophyll concentrations increased with the development of the bloom. Whelk mortality was preceded by external signs of stress including reduced ventilation, inability to attach to hard Substrates, periodic Pumping of the opercular plate, and increased mucus production over a period of 24-48 h prior to death. High concentrations (2-7 mu g g(-1) tissue) of goniodimum A, a toxin produced by A. monilatum, were observed in bivalves attached to the shells of rapa whelks. Concentrations of goniodimum A in whelk foot tissue ranged from 0.02-8.39 mu g g(-1). Mortality of rapa whelks was 100%. Mortality of oysters (Crassostrea virginica) and northern quahogs (Mercenaria mercenaria) in the same flow through system was 0%. The symptoms displayed by the rapa whelks in the 24-48 h prior to death were indicative of paralysis and followed a similar time Course documented for other molluscs exposed to toxic A. monilatum.