Dinoflagellate cysts in recent estuarine sediments from aquaculture sites of southern South Korea

Assemblages of organic-walled dinoflagellate cysts collected from 23 surface sediment samples distributed in shallow estuarine waters along the southern South Korean coast show high abundance and diversity. A total of 47 cyst types, representing 27 genera of three orders, were identified and distribution maps of the most common taxa have been produced. The cyst assemblages were dominated by Spiniferites (Gonyaulax cf. spinifera), Brigantedinium spp. (Protoperidinium spp.), and Dubridinium spp. (Diplopsalis spp.). Total cyst concentration varies from 1000 to 8900 cysts per gram of dry sediment, with the highest values observed in the most southern sites of the Marine Fish Ranching Ground (MFRG) of Dongdo Bay, near Saryang Island, and the Outer part of Buk Bay. The Inner Buk Bay and the south-western sites of the MFRG were recognized to be subjected to eutrophication, as indicated by the elevated proportional increase in cysts of heterotrophic species of the genera Dubridinium, Polykrikos and Protoperidinium.Cysts of HAB's causing ichthyotoxic Cochlodinium polykrikoides were not found in Buk Bay, and were otherwise found in most of the studied sites in low proportions, except in Gosung Bay where it comprised up to 41% of the cyst assemblage. This is in agreement with previously observed blooms of C. polykrikoides in Gosung Bay.