Species Composition Of Surface Zooplankton In The North Of Hangzhou Bay And Correlations Between Zooplankton And Environmental Factors

This study takes the surface zooplankton assemblage in the north of Hangzhou Bay as the research object, to research the species composition, seasonal changes of community structure,biological diversity and horizontal distribution. Moreover, this paper discussed the relationship with environmental factors and provides a reliable basis for estuarine waters system evaluation. Besides, a primary discussion on the relationship between zooplankton and larval and juvenile fishes will be given.Zooplankton were collected at the 10 stations in the north area(121°45′-122°09′E,30°45′-30°51′N)by a larvae net(130 cm mouth-diameter,0.5 mm mesh-aperture) during the spring tide each month from June in 2014 to May 2015. The trawling speed was 2 sea mile/hour, and each station kept 10 minutes trawling. Samples used 5% formalin to protect, and water temperature,salinity were measured on the spot. At the same time, two water samples were collected for Chl-a and DO determination.In this research, a total of 50 species were collected. Copepoda contributes the most species(18) and accounts for 36%. Medusa contributes 9 species(18%). Amphipoda contributes 4 species(8%). Mysidacea contributes 2 species(4%). Cumacea contributes 2 species(4%). Isopoda contributes 3 species(6%). Pteropoda contributes 1 species(2%). Chaetognatha contributes 2 species(4%). Polychaete contributes 2 species(4%). Decapoda contributes 4 species(8%). Euphausiacea contributes 1 species(2%). Sergestidae contributes 2 species(4%). The surface zooplankton in the north of Hangzhou Bay could be divided into four ecotypes:inshore low salinity group, eurytopic group, estuarine group, and fresh water group. However, the inshore low salinity group contributes the most species.11 species were identified as the dominant species(degree of dominance Y≥0.02) in a year.There are Acartia clausi, Acartia pacifica, Centropages dorsispinatus, Centropages sinensis, Labidocera euchaeta, Pseudodiaptomus poplesia, Tortanus vermiculus, Calanus sinicus, Paracalanus aculeatus, Paracalanus parvus and Sinocalanus sinensis.Nonetheless, Labidocera euchaeta, Pseudodiaptomus poplesia and Tortanus vermiculus were the common dominant species in four seasons.The seasonal variation of zooplankton indexes in the north of Hangzhou Bay is obviously. The species number in Summer>Spring=Autumn>Winter. The numerical value of biomass and abundance in Summer>Spring≈Autumn>Winter. The numerical range of Shannon-Wiener index is 0~2.5 in a year. The top value of this index appears in June, which reaches 1.58±0.52. The bottom value of this index appears in August, which reaches 0.66±0.37. The numerical range of Pielou index is 0~0.9 in a year. The top value of this index appears in June, which reaches 0.6±0.18. The bottom value of this index appears in July, which reaches 0.34±0.15. The bottom value of of Margalef index appears in the August, and the top value of this index appears in March.The cluster analysis and NMDS of zooplankton from 12 months show that the community structure is different between seasons. The cluster analysis and NMDS of zooplankton from 10 stations divide this area into three parts: Ⅰ is coastal water area, Ⅱ is off-shore area, Ⅲ is outside the estuary. This result gives a further instruction that the north of Hangzhou Bay area influenced by water flow movement.Combined with the environmental factors to analyses, the zooplankton community mainly affected by three factors – temperature, salinity and DO. Temperature has a significant correlation with the biomass and abundance. Salinity has a significant correlation with the species number and biological diversity. Analysis with the quantity of larval and juvenile fishes shows :surface zooplankton in north of Hangzhou Bay have no obvious relationship with the larval and juvenile fishes. However,the harmful organisms(Medusa and Chaetognatha) have a significant correlation with the quantity of larval and juvenile fish. Moreover, the increase of Medusa quantity in June may influenced the decline of larval and juvenile fishes in 2014.