Study on the dinoflagellate cysts in ballast tank sediments of international vessels in Chinese shipyards.

The problem of aquatic invasive species caused by discharge of ballast water and sediments from ships' ballast tanks has become extremely prominent. Seventeen sediment samples taken from ballast tanks of different ships docked in two Chinese shipyards were examined to identify the variety of resting dinoflagellate cysts. Twenty-two dinoflagellate cyst taxa were identified in these samples, including 11 photosynthetic and eleven heterotrophic species. These species represent 10 genera with the dominating assemblages of Alexandrium minutum, Scrippsiella acuminata, Lingulodinium polyedra, Protoperidinium sp. and Protoperidinium conicum. The total abundance of the dinoflagellate cysts ranged from 36 to 448 cysts g dry weight, which demonstrated a wide range of diversity for different ships. It was observed that the number of taxa and concentrations of cysts in ballast tank sediments were slightly greater for ships performing short voyage than ships performing longer voyage. The compositions of dinoflagellate cysts in sediments from ships sailing diverse routes were more variable than those sailing same routes. Sediment moisture content proved to be well correlated to the total cyst abundance (r = 0.7422, P < 0.01). Furthermore, nine toxic and harmful species were observed from all sediment samples, which indicated a wide range of distribution and potential risk of harmful algal blooms if being discharged to Chinese waters. As a result, full attention should be drawn to the studies on dinoflagellate cysts in the ballast tank sediments from ships arriving at China, this is of great significance for preventing introduction of toxic and harmful dinoflagellate cysts and protecting native marine biodiversity.