南沙群岛海区上层毛颚类的种类组成和丰度分布

根据南沙群岛海区1997年11月(秋季)、1999年4月(春季)和7月(夏季)3个航次的调查资料,对上层水域毛颚类的种类组成和丰度分布进行了分析。共鉴定毛颚类18种。秋、春、夏3个季节毛颚类平均丰度分别为(6.86±3.08)、(9.95±3.50)和(7.11±3.34)个/m3。肥胖软箭虫(Flaccisag-ittaenflata)、龙翼箭虫(Pterosagitta draco)和太平洋齿箭虫(Serratosagitta pacifica)是3个航次调查共有的优势种,肥胖软箭虫占绝对优势。调查海区毛颚类按其生态特征可分为暖水广布种、大洋性暖水种和暖水近岸种三个类群,前两者对毛颚类丰度分布起决定性作用。毛颚类丰度分布受东亚季风驱动的南海环流影响显著,在秋季东北季风期,毛颚类分布趋势为西高东低,高值区位于西南部,与海洋锋对应;在夏季西南季风期,毛颚类主要分布在西北部,与该区域存在的海洋锋和上升流密切相关。作为最主要的食物来源,桡足类丰度是影响南沙群岛海区毛颚类丰度变化的重要因素。

Species composition and abundance distribution of chaetognaths in the upper waters around the Nansha Islands

Species composition and abundance distribution of chaetognaths were studied based on the data obtained from three separate cruises carried out in November 1997, April and July 1999 around the Nansha Islands. A total of 18 species were identified and the number of species did not show obvious seasonal variation.The abundance of chaetognaths ranged from 1.60 to 16.40 ind/m³ with the average of (6.86±3.08) ind/m³ in autumn,(9.95±3.50)ind/m³ in spring and (7.11±3.34)ind/m³ in summer. Flaccisagitta enflata dominanted, Pterosagitta draco and Serratosagitta pacifica followed during three seasons.Chaetognaths could be classified into three ecological groups, i.e.,the widespread warm-water species, the oceanic warm-water species and the nearshore warm-water species, in which the first two groups played a decisive role in the quantity distribution of chaetognaths. The seasonal distributions of chaetognaths were related to the southern South China Sea circulation driven by East Asian monsoon. During NE monsoon in autumn, the distribution of chaetognaths density showed decreasing tendency from the west to the east, and the high value spots were at oceanic fronts in southwestern survey area. In summer, the high density of chaetognaths was found in the northwest, where the upwelling and the oceanic fronts were induced by SW monsoon.