Blooms of the dinoflagellate Ceratium hirundinella in large enclosures placed in Lake Biwa

Abstract

Blooms of the dinoflagellate Ceratium hirundinella in large enclosures placed in Lake Biwa were followed from late July to mid September 1996 with special reference to the physico-chemical environment. We detected two blooms of C. hirundinella. The first occurred during a low dissolved inorganic nitrogen (DIN) period. C : N molar ratios of seston, however, indicated that phytoplankton were not limited by nitrogen during that period. The occurrence of the first bloom of C. hirundinella was attributable to the ability of the dinoflagellates to use scattered nutrient sources, since the literature has noted theoretically that large-sized, motile algae such as C. hirundinella are superior to other phytoplankters in exploiting the environmental heterogeneity of nutrient distribution. The second bloom commenced after a fresh supply of DIN due to rainfall when the abundance of C. hirundinella was still comparatively high among that of phytoplankton. Hence, it is likely that the flagellate advantageously utilized the supplied DIN, suggesting that the abundance of C. hirundinella in the present study was controlled by nitrogen availability.