Seasonal and long-term dynamics of sand-dwelling dinoflagellates (Dinoflagellata) in Peter the Great Bay, the Sea of Japan
The seasonal and long-term dynamics of the species composition and abundance of dinoflagellates dwelling in subtidal sands in Russian waters of the Sea of Japan was studied for the first time. The overall species composition of sand-dwelling dinoflagellates in Peter the Great Bay was represented by 67 taxa belonging to 25 genera. Among them, 17 species were recorded for the first time from the seas of Russia, and 8 species were found from the Pacific coast of Russia for the first time. The greatest number of species belonged to the genera Amphidinium, Amphidiniopsis, and Thecadinium. A list of the species composition, including distribution of taxa throughout the localities and seasons, is presented. Most species of the microalgae are illustrated by light and scanning electron micrographs. The species richness varied from 18 to 44 during the year. In winter, at a water temperature less than 0<sup>o</sup>C, the species richness of sand-dwelling dinoflagellates (24-26 species) roughly coincided with that found in summer (20-44 species). The average abundance of dinoflagellates ranged from 16 to 1121 cells/cm<sup>3</sup> across localities and throughout the year. During the annual cycle, the highest cell abundances (595 and 2576 cells/cm<sup>3</sup>) were recorded in the winter-spring period and a slight increase in abundance was observed in fall. This was due to the high densities of dominant species Amphidiniopsis uroensis and Thecadinium kofoidii. Sand-dwelling dinoflagellates contributed 58 to 80% to the total annual abundance of the subtidal microphytobenthos in different localities of Peter the Great Bay.