Dynamic Changes in the Ichthyoplankton Community Structure after the Sluice of the Three-Gorges Dam

An analysis was made of the data obtained in comprehensive surveys on the fisheries ecology and oceanography in the Changjiang River estuary.Eleven species of ichthyoplankton were recorded with 35 eggs and 29 larvae in November,2002,while 14 species were recorded with 24 eggs and 85 larvae in November,2003,which showed the species and quantities of ichthyoplankton in 2003 were more than those in 2002, and the ichthyoplankton community structure and its spatiotemporal dynamics were notably changed.The species of Sciaenidae were more than the others;Anguillidae,Callionymus spp.and Pseudosciaena crocea were new records in 2002.There were relatively more species of Sciaenidae in 2003;Anchoviella commersoni was a new record in 2003,but it was an absolutely dominant species,acconting for ca 64.2% of all the ichthyoplankton samples.In addition,Odontamblyopus rubicundus,Anchoviella zollingeri,Enedrias fangi,Pseudolaubuca engraulis,Chirocentrus dorab,and Trachinocephalus myops were all new records in the investigation area.Some species,such as Enedrias fangi in the Huanghai and Bohai Seas appeared in 2003 in the East China Sea,and some species changed their reproductive time.Based on their indices of relative importance,it can be seen that Sciaenidae,Salanx ariakensis and Lateolabrax japonicus were the dominant species in 2002,while Anchoviella commersoni,Saurida undosqamis and Trachinocephalus myops were the dominant species in 2003.Engraulis japonicus was absolutely dominant quantity historicals,but recent 2 years investigations,shoneed that it had changed from a dominant species to an ordinary species.The above changes in ichthyoplankton community structure weere related to runoff,overfishing and pollution etc.,but runoff is the most important factor that can cause changes in temperature,salinity etc.,especially the construction of the Three-Gorges Dam,which has changed the runoff of the Changjiang River since the first sluice.So the changes in icthyoplankton species and quantity reglected the environmental factors changes in the ecosystem.The research of ichthyoplankton can provide dynamic monitoring for the influence of the Three-Gorges Dam on the estuary ecosystem.