MORPHOLOGICAL AND NUCLEAR ANALYSIS OF THE BLOOM‐FORMING DINOFLAGELLATES GYRODINIUM CF. AUREOLUM AND GYMNODINIUM NAGASAKIENSE1

Abstract

ABSTRACTTwo red‐tide forming naked dinoflagellates, the Japanese species Gymnodinium nagasakiense Takayama et Adachi and the north European species Gyrodinium cf. aureolum Hulburt, were compared with regard to their external morphology, chromosome number and DNA content. Morphological studies were performed using both light and scanning electron microscopy; analytical flow cytometry was used to compare DNA contents. Our strains of G. cf. aureolum and G. nagasakiense were morphologically indistinguishable, and both closely fit the original description of the latter species. In contrast, several details, including the shape and position of the nucleus, differed between our strains and the original description of Gyrodinium aureolum. However, despite an equal number of chromosomes, the Japanese taxon possessed about 40% more DNA than the European one. Moreover, the latter taxon was able to form two subpopulations of vegetative cells, which we called “small” and “large,” whereas the former one only formed “large” cells. These discrepancies cast doubt upon the conspecificity of G. cf. aureolum and G. nagasakiense. The appellation Gymnodinium cf. nagasakiense is therefore proposed for the species encountered in the northern European seas, waiting for a future reconsideration of both the genera and the species.