| Based on the data collected from four oceanographic surveys in the east area of north(121.67°E~121.87°E, 30.68°N~30.83°N), the east area of south(121.60°E~121.85°E, 29.95°N ~ 30.24°N), the west area of north(121.31°E ~ 121.56°E, 30.58°N ~ 30.77°N) Hangzhou Bay and outside the bay(122.10°E ~ 122.58°E, 30.54°N~30.93°N) during the autumn of 2009, 2011, 2012 and 2012, we analyzed the species composition, ecological groups and similarity of the zooplankton community inside the bay, as well as the influential factors were explored. We also analyzed the distribution patterns and composition of dominant zooplankton species in the three areas. Effects of the tide, water masses, and environmental factors on the distribution patterns of zooplankton were explored. In addition, this paper analyzed and compared the differences on community composition, K-dominance curves and diversity index(H’) of zooplankton community structure characteristics outside and inside the bay. The main results were as follows:(1) A total of 14 species in 6 groups were identified in the west area of north Hangzhou Bay. As the dominant specie, Tortanus vermiculus had an important impact on the total abundance. The zooplankton fauna was exclusively of the subtropical estuarine brackish-water type, accounting for 79.84% in the total abundance, which was influenced by the runoff strength of the Qiantang River. 19 species in 6 groups were identified in the east area of north Hangzhou Bay. The most influential factors on the complex taxonomic structure and eco-group composition of the zooplankton fauna was the impact of the runoff strength of the Yangtze River and seawater invasion from the East China Sea. The dominate eco-group type were warm temperature and subtropical nearshore low-salinity species, accounting for 43.46% and 31.14% in the total abundance. In the east area of south Hangzhou Bay, 25 species in 7 groups were identified. The dominate eco-group type were subtropical nearshore low-salinity and subtropical nearshore species, accounting for 72.31% and 18.34% in the total abundance. And the maximum contribution for ecological groups of species was Labidocera sinilobata, accounting for 65.32% in the total abundance. By hierarchical cluster analysis and non-metric multidimensional scaling(NMDS) method, the results indicated that the zooplankton community in the three parts of Hangzhou Bay was clearly different, which was related to the water masses.(2) The total biomass increased gradually from nearshore to offshore in the west area of north Hangzhou Bay, while the total abundance increased from offshore to nearshore. In the east area of north Hangzhou Bay, the total biomass increased from offshore to nearshore, however the peak abundance occurred in the central survey waters. In the east area of south Hangzhou Bay, both the total biomass and total abundance increased from offshore to nearshore. The average biomass of zooplankton in the west and east areas of north Hangzhou Bay and the east area of south Hangzhou Bay were 70.78 mg·m-3, 84.10 mg·m-3, and 580.58 mg·m-3, respectively. The average abundance in the three areas were 47.98 ind·m-3, 98.89 ind·m-3, and 578.88 ind·m-3, respectively. The analysis of variance shows that there were a significant difference in the zooplankton abundance in the different parts of Hangzhou Bay; and there were a significant difference in dominant species in the three areas as well. The primary dominant specie in the west area of north Hangzhou Bay was Tortanus vermiculus; Labidocera euchaeta and Paracalanus aculeatus in the east area of north Hangzhou Bay; and Labidocera sinilobata in the east area of south Hangzhou Bay. The difference in zooplankton distribution in the three areas may be majorly influenced by the runoff strength of the Yangtze River and Qiantang River, seawater invasion from the East China Sea, and the difference of tidal currents between the north and south parts. The association between the distribution of zooplankton and environmental parameters, which was calculated by the stepwise regression analysis, indicates that temperature and salinity are the two major factors that influence the distribution pattern of zooplankton in the three different parts of Hangzhou Bay.(3) By comparison, there were large differences between the community composition of zooplankton outside the bay and those in the other three waters within the bay. It was a mixed community which was composed of nearshore species such as Pseudeuphausia sinica and nearshore low-salinity species such as Centropages dorsispinatus in the communityⅠ outside the bay, followed by offshore species. The community Ⅱ of the east area of south Hangzhou Bay was composed of nearshore low-salinity species such as Labidocera sinilobata, followed by nearshore species. The community Ⅲ of the east area of north Hangzhou Bay was mixed with nearshore low-salinity species such as Labidocera euchaeta and estuarine brackish-water species such as Tortanus vermiculus. In the community Ⅳ of the west area of north Hangzhou Bay, as the dominant species, Tortanus vermiculus of estuarine brackish- water species had the highest proportion, which was different from the communityⅠ. Generally, the community with a lower salinity adaptability were appeared to the west and north direction of the area. According to the K-dominance curves, dominance curve of communityⅠand community Ⅲ both rose quite gentle. In addition, the initial cumulative dominance of community Ⅲ was higher than that of communityⅠ. While, compared with the community Ⅰ, the initial cumulative dominance of community Ⅱ and community Ⅳ were far higher than that of communityⅠ. As the initial cumulative dominance of communityⅠ outside the bay was particularly in a low level, which showed that there were many types of dominant species in community Ⅰ, and the dominance of a single dominant specie was lower than those of the communities inside the bay. And the results of variance analysis indicated that there were highly significant differences between the diversity index of zooplankton outside the bay and those in the other three waters within the bay(P<0.01). Meanwhile, there was no significant difference between the three waters of the bay(P>0.05). It showed that the diversity index of zooplankton outside the bay was higher than those of the communities inside the bay. The main reason which caused the big difference in community of zooplankton between inner and outer waters of the bay was due to the difference of the influence of dominant water masses in each water. |
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