Ecological Study On Zooplankton In The Spring Of Jiulong River Estuary

Base on the data collected from12cruises conducted in2011(March to May) and2012(March to June), species composition, abundance variation and spatio-temporal distribution of zooplankton community in the spring of Jiulong River Estuary were analyzed. By contrasting the results between ebb and flood tide, the tidal effect on the spatial distribution of zooplankton in the Jiulong River Estuary was analyzed as well.In recent years, there is an increasing trend of Blackfordia virginica in the Jiulong River Estuary. Considering its strong ecological adaptability, a greater understanding of the biology of B. virginica is needed to recognize its effects on estuarine ecosystems and to develop control strategies, if necessary. Therefore, the distribution characteristics of B. virginica in the Jiulong River Estuary were focused on.The main results were as follows:1、Species composition and abundance variation of zooplankton in the Jiulong River Estuary in springIn2011,6surveys were conducted at ebb tide from March to May.47zooplankton species and15groups of planktonic larvae were recorded, belonging to copepods, hydromedusae, malacostracans and other6taxa. The zooplankton abundance varied greatly in the3stations at different cruises, and the mean abundance was298.49ind./m3.5dominant species (groups) were found, which were Pseudodiaptomus poplesia, Labidocera euchaeta, Acartia spp., Tortanus dextrilobatus and zoea larvae of Brachyura, respectively.The surveys in2012were conducted at flood tide from March to June.72zooplankton species and15groups of planktonic larvae had been identified. The species composition was similar to the result of2011. But the species number of copepods and hydromedusae were higher than that in2011. The mean abundance of zooplankton was2534.16ind./m3. There were6dominant species (groups) in2012. Compared to2011, Acartiella sinensis was another dominant species in the investigated area. And P. poplesia was the absolute dominant species (H’=0.55).2. Tidal effect on zooplankton community in the Jiulong River Estuary.The tidal effect had a great influence on the estuarine zooplankton community. The species number and abundance of zooplankton at flood tide were both significantly higher than those at ebb tide. Meanwhile, the spatial distribution of zooplankton was significantly affected by the tide. At ebb tide, low-salinity species like P. poplesia and B. virginica could spread to the M5station. While at flood tide, these low-salinity species mainly distributed in the upper estuary.3. The temporal and spatial distribution of B. virginica in the Jiulong River EstuaryIn the spring of2011, the average number of B. virginica was3.09ind./m3in the investigated area, accounting for0.8%of the total zooplankton abundance. And the highest value (11.46ind./m3) appeared in May8, which consisted of82.0%abundance of hydromedusae and3.2%of zooplankton.While in the spring of2012, the average number of B. virginica was62.2ind./m3, accounting for5.4%of the total zooplankton. The highest value (303.8ind./m3) appeared in May4, consisting24.7%of zooplankton abundance.Both in2011and2012, B. virginica began to appear in late April, then the population reached peak in the early of May. After then its number began to fall. The population number of B. virginica was mainly influenced by SST(Sea Surface Temperature). It began to appear when the SST reached20℃, then the population grew as the SST rose. When SST reached22℃or so, its population reached peak, but the population number decreased sharply when SST exceeded24℃. B. virginica mainly distributed in the area between the Station M1and Station M3, few were found in the Station M5.