Characteristic Comparison Of Fish Larval And Juvenile Assemblages Between The Surf Zones Of South Branch Of Yangtze River Estuary And North Coast Of Hangzhou Bay

Based on the survey in the surf zones of both south branch of Yangtze River estuary and north coast of Hangzhou Bay, species composition, spatial-temporal distribution and biodiversity characteristics were compared between two areas,relative factors were discussed.During August 2009 to August 2010, fish larvae and juveniles were monthly collected around the spring tide period by a seine net(1m×4m, 1mm mesh-aperture) at 12 stations in surf zones of both south branch of Yangtze River estuary and north coast of Hangzhou Bay. A total of 14907 fish larvae and juveniles were collected representing 74 species from 24 families.A total of 11066 individuals belonging to 40 species from 11 families were collected in surf zones of south branch of Yangtze River estuary. The most dominant species was Coilia nasus which comprised 64.44% of the total catches in Yangtze River estuary. Species richness of estuarine species and limnetic species were relatively higher, which were 17 and 18 respectively. The migrating species was most abundant which comprised 64.88% of the total catches. Individuals of flexion stage(33.32%) were ratherish more than other development stages.A total of 3841 individuals belonging to 59 species from 23 families were collected in surf zones of north coast of Hangzhou Bay. The most dominant species were Acentrogobius pflaumii and Eleutheronema rhadinum, which respectively comprised 39.91% and 21.82% of the total catches. Estuarine species was predominant in term of species richness and abundance(28 species, 77.09%). Individuals of post-flexion stage dominant the total catches(63.93%).Species richness and density showed no significant differences between two areas and among the stations within each area (P>0.05), while the differences among months were significant (P<0.05). The variation among months positive correlated with temperature significantly (P<0.05), the correlation with salinity was not significant (P>0.05). Combined with the result from hierarchical cluster, salinity was proved to be the main factor to determine the difference between two areas. Substrate and landform also affected the distribution of fish larvae and juveniles within each area. 12 stations were grouped into two groups through IndVal method which contructed 9 and 16 representative species for Yangtze River estuary and Hangzhou Bay respectively. According to the patterns of spatial-temporal distribution of representative species, 3 type of fish larvae and juveniles utilizing surf zone were separated: (a) Utilizing surf zone as a nursery ground, (b) temporally inhabited in surf zone, (c) occurred in surf zone all-year. All the 3 types were observed in surf zones of Yangtze River estuary, whereas the type c was not observed in surf zones of Hangzhou Bay.Biodiversity of fish larvae and juveniles assemblage in surf zone of Hangzhou Bay was higher than surf zone of Yangtze River estuary.βw value between two area equal to 0.664, and the Bray-Curtis dissimilarity reached to 0.925, showed considerable difference between two area.βw values among months range widely, due to the events of fish occurrence in surf zone around Mar-May and leaving surf zone around Oct-Nov, thus theβw values among months presented a bimodal curve. Biodiversity of estuarine species and limnetic species were higher than marine species and migrating species. Hαwas sharply decreased withαapproaching infinity, due to several dominant species absolutely predominanting in catches.