IDENTIFICATION OF A DOMOIC ACID-PRODUCING PSEUDO-NITZSCHIA SPECIES (BACILLARIOPHYCEAE) IN THE DUTCH WADDEN SEA WITH ELECTRON-MICROSCOPY ANDMOLECULAR PROBES

Biological monitoring in the Dutch Wadden Sea between November 1993 an d July 1994 revealed Pseudo-nitzschia-like pennate chain-forming diato m species with cell numbers ranging from 10(2) to 10(5) per litre. Cul tured isolates and field samples were examined by electron microscopy, which revealed the majority to be Pseudo-nitzschia pungens. This spec ies dominated over other diatoms in the phytoplankton population durin g November 1993 and at the end of June 1994. At the beginning of June 1994, P. fraudulenta was also present; occasionally, P. delicatissima was observed. One isolate showed the characteristic morphology of P. m ultiseries. Species-specific polyclonal antibodies and large-subunit ( LSU) rRNA-targeted oligonucleotides for North American strains of P. m ultiseries and P. pungens applied to the European isolates, confirmed species designations based on electron microscopy. The isolate of P. m ultiseries from the Dutch Wadden Sea produced domoic acid; after 55 da ys of growth about 19 pg per cell was measured This is the first repor t of a domoic acid-producing P. multiseries isolated from European coa stal waters.