CHATTONELLA AND FIBROCAPSA (RAPHIDOPHYCEAE) - FIRST OBSERVATION OF, POTENTIALLY HARMFUL, RED TIDE ORGANISMS IN DUTCH COASTAL WATERS

Species of the potentially toxic and red-tide-forming marine-phytoplan kton genera Chattonella and Fibrocapsa (Raphidophyceae) were observed for the first time in 1991 in samples taken in Dutch coastal waters; t hey were again recorded and enumerated in the following years. Chatton ella spp. cell numbers varied with the season, with a maximum in May o r June in the Dutch Wadden Sea. Cell numbers of Chattonella and F. jap onica Toriumi et Takano were up to 6.0 . 10(3) cells . dm(-3) in the D utch Wadden Sea, except at one station in June 1993 when over 10(4) ce lls . dm(-3) Chattonella were counted. In May 1993, a minor bloom (ove r 2.0 . 10(5) cells . dm(-3)) was observed at a station in the souther n central North Sea, 100 km northwest of the island of Terschelling. T he potentially neurotoxic species Chattonella marina (Subrahmanyan) Ha ra et Chihara was identified and discriminated from morphologically re lated species within the class of Raphidophyceae by immunofluorescence . F. japonica could only be clearly identified in live samples; in fix ed samples cell morphology was severely affected. The identification o f this species was supported by the presence of mucocysts, structures that can be observed readily by optical and electron microscopy.