南沙群岛渚碧礁春季浮游动物群落特征

ZOOPLANKTONIC COMMUNITY CHARACTERISTICS IN WATERS OF ZHUBI CORAL REEF (NANSHA ISLANDS) IN SPRING

根据2002年5月的调查资料,对南沙群岛渚碧礁浮游动物的群落结构、平面分布、垂直分布和昼夜变化等进行了研究分析。浮游动物鉴定有72种,其中挠足类种数最多,其次是浮游幼虫、毛颚类。浮游动物种类中多数是终生浮游生物,少数是阶段性浮游生物,个别是暂时性浮游生物。渚碧礁浮游动物群落的热带特征非常显著,多数种类属于热带外海生态类群,少数属于暖水沿岸生态类群。优势种相当突出,其中奥氏胸刺水蚤Centropagesorsinii占主导地位。渚碧礁浮游动物平均密度达840个·m-3,礁坪区与湖内的浮游动物数量分布差异很大,湖为礁坪的7倍多,两者的优势种也有明显差异。浮游动物垂直分布不均匀,主要密集于5—10m水层,因种类不同其垂直分布也有差异。礁坪的浮游动物种类和数量昼夜变化显著,均呈白天减少、夜晚增加。浮游动物的数量分布与环境因子和浮游动物生态习性有关。

The community structure, abundance, vertical distribution, diel variation of zooplankton around Zhubi coral reef of Nansha Islands sea area were studied during the cruise carried out in May, 2002. Seventy-two species of zooplankton have been identified up to the present. Copepod dominated over the zooplankton community in terms of both species diversity and numerical abundance, followed by pelagic larvae and chaetognatha. Most of the zooplankton species belonged to holoplankton, and some belonged to meroplankton and few to tychoplankton. The zooplanktonic community around Zhubi coral reef has obviously tropic characters and was dominated by the tropical oceanic groups, only few species belonged to neritic warm water groups. Centropages orsinii was the most abundant species. An average zooplankton abundance of 840 ind·m^(-3) was recorded here. Evident differences were found in abundance and dominant species between the reef flat and the lagoon, and the abundance in the lagoon was 7 times more than that in the reef flat. Referring to the vertical distribution, the species concentratedly distributed in the water layer between 5 and 10 meters and the distribution showed different between species. The diel changes of species and abundance were obvious at the reef flat, and the species diversity and abundance were larger in the nighttime than in the daytime. The relationship between the distribution of zooplankton abundance and the environmental factors and ecological habits of zooplankton was discussed.