Larval Crassostrea bivalve and Artemia brine shrimp bioassays to assess toxicity and micropredation by the heterotrophic dinoflagellates Cryptoperidiniopsis brodyi and Pfiesteria piscicida from Australian waters

摘要

The capability of the heterotrophic Australian marine dinoflagellates Cryptoperidiniopsis brodyiudand Pfiesteria piscicida to impact on larval Pacific oyster (Crassostrea gigas) and brine shrimpud(Artemia salina) nauplii was investigated. An attractant response of the heterotrophs towardudactively swarming Artemia was not observed and no mortality occurred. In contrast, the dinoflagellatesudbecame active and exhibited attacking behavior toward planktonic oyster larvae (below 1 mmudsize) within a few seconds. The oyster larvae survived 2500 cells mL21 for 2 days, but mortalityudincreased to 82–88% by day 12. Aqueous dinoflagellate cell extracts collected from the bioassayudthat induced oyster kills were tested in a further larval bivalve bioassay but no mortality wasudobserved. Oysters over 2 mm in size survived the physical attack by the heterotrophs and remainedudalive during the bioassay period. Changes in zoospore and cyst abundances in the presence of oysterudlarvae were also documented. More actively swarming zoospores and 2.5-fold higher cell numbersudwere produced in the presence of oysters compared to control cultures. These results indicate thatudmortalities of the planktonic larvae can be induced by micro-predatory feeding behavior ofudC. brodyi and P. piscicida.