Diarrhetic shellfish toxicity in relation to the abundance of Dinophysis spp. in the German Bight near Helgoland

Abstract

Diarrhetic shellfish toxicity is caused by the accumulation of okadaic acid and its deriv- atives, which are produced by particular species of Dinophysis Ehrenberg 1839 and Prorocentrum Ehrenberg 1833 (Dinoflagellata). In the German Bight (North Sea) around the island of Helgoland, 4 toxic Dinophysis species occur, of which 2 exhibited successive biomass maxima in summer 2000 (D. norvegica Claparede et Lachmann 1859 with cell concentrations of max. 400 cell l -1 and D. acumi- nata Claparede et Lachmann 1859 with max. cell concentrations of over 4000 cells l -1 ). In contrast to findings in other marine areas, toxicity of Mytilus edulis Linne 1758 could be clearly attributed to the observed increases in cell abundances of both species. In several Mytilus samples toxin concentra- tions (max. 460 ng diarrhetic shellfish poisoning (DSP) toxins g -1 hepatopancreas) were in a range which is considered dangerous for human consumption. While mussel toxicity coincided with concentration increases of both Dinophysis species, toxicity of the particulate substance in the water (max. 26 ng l -1 ) could be detected only during cell concentration maxima of D. acuminata. Mussel toxicity lasted 3 wk after the end of the D. acuminata bloom, and this is attributed to extended toxicity of decaying Dinophysis cells and detritus. Elevated summer temperatures and low silicate concen- trations evidently supported the development of high concentrations of D. acuminata.