南沙群岛西南大陆斜坡海域浮游动物的垂直分布

浮游动物是海洋生态系统物质和能量转移的关键环节,也是渔业资源的重要饵料,其种类组成和数量分布均有明显的垂直分层现象。利用2011年4月在南沙群岛西南大陆斜坡海域开展的18个站点90份样品的调查数据,对该海域浮游动物的垂直分布进行了研究,表明:(1)该海域浮游动物种类组成丰富,共出现18个类群580种(类);(2)浮游动物种类组成垂直变化明显,特定水层出现的种类数占总种数的43.6%,各水层均出现的种类仅占总种数的15.8%;(3)优势种组成复杂,垂直变化明显,单一种类的优势度不高;(4)浮游动物平均密度和湿重生物量分别为206.27ind/m3、94.03mg/m3,密度和生物量均以0~2m层和30~75m层较高,沿水深梯度的变化呈明显的双峰型;(5)浮游动物数量的垂直变化主要受温跃层影响,温跃层内浮游动物数量最高,温跃层上方和下方的水层内数量较低;(6)南沙西南大陆斜坡区浮游动物生产力水平较高,表明该海域渔业资源有一定的开发潜力。

Vertical distribution of zooplankton in the continental slope southwest of Nansha Islands, South China Sea

As dietary organisms of fish stocks, zooplankton is a key link of mass and energy transformation in the marine ecosystem. There are vertical changes in the species compositions and abundances of zooplankton in the water column. Based on 90 samples from 18 stations collected in April 2011, the vertical distribution of zooplankton in the continental slope to the southwest of Nansha Islands, South China Sea was studied. It was found that the continental slope waters are rich in zooplankton species, with a total number of 580 species belonging to 18 taxa being recorded. There are obvious vertical variations in the zooplankton species compositions. The numbers of zooplankton species occurring in a specific deep group could take up 43.6% of the total number of species, while the number of species occurring in all deep groups made up only 15.8% of the total number of species. There was no obvious dominant species and the dominancy of any single species was low. The overall mean density and wet biomass of zooplankton were 206.27 ind/m³ and 94.03 mg/m³ respectively. The higher density and biomass were found in the deep groups of 0-2 m and 30-75 m and the vertical distribution showed a pattern of double-humped curve. Thermocline was an important factor in the vertical distribution of zooplankton. The abundances of zooplankton in the thermocline layer were higher than those in the upper mixed layer and the water layers bellow the thermocline. Compared to the other regions in the South China Sea, zooplankton abundances were the highest in the continental slope southwest off Nansha Islands, suggesting potentials for fishery development in the region.