Dinoflagellate genus Cochlodinium Schütt has been documented to form blooms along the coastlines of many countries and caused mass mortalities of fish or shellfish.From October to November,2009,harmful algal blooms(HABs)caused by dinoflagellate Cochlodinium geminatum broke out in the coastal waters in Zhuhai,Guangdong.The bloom covers more than 300 km².In order to understand the toxicity of the bloom water,and provide some basis to the algae bloom management and further study of this species,acute toxicity of the bloom water against larvae of zooplankton Artemia salina,fish Scatophagus argus and shrimp Penaeus vannamei was investigated under room conditions.Moreover,feeding rate of A.salina on C.geminatum was also investigated in this paper.The results showed that LC₅₀(Median Lethal Concentration)of C.geminatum against A.salina larvae was 9.55×10⁴/mL within 24 h.LT₅₀ of C.geminatum against A.salina larvae decreased with the increasing cell density.LT₅₀ of C.geminatum with cell density of 2.5×10³/mL against A.salina larvae was 48.5 h.No adverse effects of C.geminatum on the survival of fish and shrimp larvae was observed within 60 h.On the other hand,it was found that both A.salina and S.argus larvae could feed on C.geminatum.But the feeding rate of A.salina larvae was low.Overall,the bloom water of C.geminatum caused an impact on the survival of A.salina.C.geminatum with high cell density could cause mass mortality of A.salina larvae.However,A.salina could live on low cell densities of C.geminatum.Causes of the death of A.salina larvae may not be due to the ingestion of C.geminatum.C.geminatum caused acute toxicity neither against the S.argus larvae nor against the P.vannamei larvae.