| The distribution of zooplankton in the area of radiate sand ridges in north Jiangsu shoal was investigated during May and September in 2012. The relationship between the distribution of zooplankton, topography and some other environmental factors were analyzed by using indicators and methods of gathering strength, variance contribution, dominance index, stepwise regression, etc. The results showed that both of the biomass and abundance of zooplankton have obvious seasonal variation. Spatially, the quantity of zooplankton was higher in sand ridges than that in tidal creeks. In spring, the average biomass of different areas were 606.63 mg·m-3(sand ridges), 428.00 mg·m-3(shallow tidal creeks) and 178.55 mg·m-3(deep tidal creeks). The average abundance were 560.76 ind·m-3(sand ridges), 389.39 ind·m-3(shallow tidal creeks) and 161.28 ind·m-3( deep tidal creeks). However, in autumn, the average biomass of different areas were 208.01 mg·m-3(sand ridges), 181.30 mg·m-3(shallow tidal creeks) and 60.47 ind·m-3(deep tidal creeks). And the average abundance were 184.15 ind·m-3(sand ridges), 56.42 ind/m3( shallow tidal creeks) and 112.14 ind·m-3(deep tidal creeks). The study showed that the Copepods was predominant species in two seasons. The research indicated that the distribution of zooplankton was associated with topography and tidal waves in the north Jiangsu shoal. Some reasons can explain it. Firstly, the water velocity was influenced by the topography, where the water velocity was higher in sand ridges than tidal creeks. Secondly, the East China Sea tidal wave and the South Yellow Sea tidal wave converged in north Jiangsu shoal. Sediment can be deposited easily in low flow velocity water, and upwelling waters brought a wealth of nutrients. It would be beneficial to the aggregation and feed of zooplankton, which lead to high biomass and abundance of zooplankton in sand ridges. The dominant species tend to be highly aggregated, which contributed to the main component of economic fishes’ bait. The food availability and quality of north Jiangsu shoal were higher than other water areas, which played a crucial role in the formation of Lüsi Fishing Ground.The community structure of zooplankton in the area of radiate sand ridges in north Jiangsu shoal was investigated during May and September in 2012. The zooplankton community was divided through methods such as clustering, sorting. The seasonal changes of ecological groups of zooplankton were analyzed from ecological adaptation, species numbers, abundance and K-dominance curves. The results showed that the zooplankton community of spring and autumn were divided into two different zooplankton fauna. There were same number of warm-temperature nearshore low-salinity species(2 spieces) and warm-temperature nearshore species(10 spieces) in both spring and autumn. The similarity of warm-temperate species in the two seasons indicated that the north Jiangsu shoal were typical warm-temperate waters. With seasonal changes, the proportion of subtropical species increased from 40%(in spring) to 60%(in autumn), which owing to the impacts of temperature rise, the change of direction of Yangtze diluted water and the propelling movement of the East China Sea tidal wave. The warm temperate species’ abundance in spring was 325.62 ind·m-3, accounting for 97.81% in the total abundance, which became the most important ecological groups in spring. Although the abundance of subtropical species increased significantly in autumn, the abundance of warm-temperate species(76.24 ind.m-3) was still higher than the subtropical species(45.06 ind.·m-3). Therefore, whether it was spring or autumn, the dominant eco-group types were warm temperate species in north Jiangsu shoal. This area had the character of typical warm temperate climate. The external cause of the presentation that the abundance of zooplankton in spring was extremely higher than in autumn was warm-temperature geography environment, and the inherent reason can be summarized as ecological adaptation of zooplankton. The feature of the abundance made the spring of north Jiangsu shoal so important, that was why Lvsi Fishing Ground became the excellent spawning ground of the East China Sea and Yellow China Sea.Based on the zooplankton samples gathered in the area of radiate sand ridges in north Jiangsu shoal during May& September 2012, this paper divided the zooplankton communities through clustering and sorting method, analyzed the effect of topography factors on zooplankton community from differences in species composition, species number, the amount of abundance, ecological adaptability and the dominant species, etc. The results showed that zooplankton in spring and autumn can both be divided into two communities— sand ridges community(Ⅰ) and tidal creek community(Ⅱ). From species numbers aspect, spring tidal creeks zooplankton community SpⅡ’s total number of species(18 species), warm temperate species(11 kinds) were both higher than the sand ridge Community SpⅠ(16 species, 8 kinds). At the same time, autumn tidal creek zooplankton communities AuⅡ’s total number of species(27 species), warm temperate species(10 kinds), subtropical various class number(17 kinds) were all higher than the sand ridge community AuⅠ(18 species, 6 kinds, 12 kinds). What cause it happened may be the different height between tidal creeks and sand ridges. When zooplankton carried by current in different directions from the outside to the center of the sand ridges, part of the species left in the bottom of the tidal creeks because of the different height of topography. From abundance aspect, both of the abundance of spring sand ridges Community SpⅠ(607.57 ind·m-3) and autumn sand ridges community AuⅠ(145.36 ind·m-3) were all higher than spring tidal creek community SpⅡ(241.31 ind·m-3) and autumn tidal creeks community AuⅡ(113.89 ind·m-3) respectively. It showed the seam feature on the abundance of warm temperate species and subtropical species as well. This probably associated with the water velocity which effected by topography. Sand ridges featured by low water velocity, which would be benefit for the aggregation and feed of zooplankton. Spatially, the South Yellow Sea rotation tidal were stronger under the influence of northerly winds in spring, making sand ridge Community SpⅠ’ s position south. On the contrary, in autumn, southeast winds made the East China Sea tidal wave stronger, which lead to the area of sand ridge community AuⅠnorthward. From dominant species aspect, tidal creeks community dominance dominant species tend to be higher off of pelagic species, such as Calanus sinicus. While some sand ridges community dominance dominant species were higher to be benthonic species, like Acanthomysis brevirostris. There are also similar differences in species composition. Main endemic species of spring sand ridges zooplankton community SpⅠmay tend to be benthic, while main endemic species of spring tidal creek community SpⅡ may frequently be floating. Meanwhile, endemic species of autumn sand ridges zooplankton community AuⅠwere all near shore and estuarine species, and autumn tidal creek community AuⅡ were primarily offshore species. In summary, the topography of sand ridges and tidal creek system was the main reason for the formation of different communities in North Jiangsu shoal. |
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