北部湾西北部饵料浮游动物季节变化及其与鱼卵、仔稚鱼的关系

Seasonal variation in zooplankton characteristics and their relationship with fish eggs and larvae in the Northwest Beibu Gulf

根据2012年在北部湾西北部广西近海冬、春、夏和秋4个季节的调查资料,探讨了该海域浮游动物总丰度的平面分布、季节变化及鱼卵仔稚鱼的丰度的季节变化,结果表明,调查水域浮游动物的丰度在春夏、秋冬季变化较大,而在冬春与夏秋季变化较小,浮游动物在冬、春、夏、秋四季的平均丰度分别为337.35 ind/m3、280.01 ind/m3、4.32ind/m3和14.78 ind/m3,冬春季明显高于夏秋季,浮游动物数量高峰季比东海提前了一个季节。冬春两季,浮游动物的数量分布特征相近,在湾内和沿岸水域数量高于近海水域。相反,在夏秋季,丰度在近海水域明显高于沿岸及湾内水域。浮游动物在各季节不同的分布特征与该海域沿岸水、外海水和混合水的季节性变化有关,优势种经历了由春季的沿岸暖温种到夏季和秋季的外海暖水种到冬季的沿岸暖水种更替的过程。该海域的主要优势种,冬季为鸟喙尖头溞(Penilia avirostris),春季为中华哲水蚤(Calanus sinicus),夏季和秋季同为肥胖软箭虫(Flaccisagitta enflata),主要优势种类的生态适应性决定了浮游动物总数量的分布特征。鱼卵、仔稚鱼在冬、春、夏、秋季的丰度为6.83 ind/m3、3.09 ind/m3、0.05 ind/m3、0.20 ind/m3,季节变化趋势与浮游动物一致,由高到低依次为冬季、春季、秋季、夏季,两者较强的正相关关系表明,食物饵料充足对鱼卵仔鱼的发育具有促进作用。

This paper addresses the spatiotemporal distribution characteristics of zooplankton abundance and seasonal changes in fish egg and larval density based on data from four oceanographic surveys in Guangxi offshore waters in the Northwest Beibu Gulf during the winter, spring, summer, and autumn of 2012. Additionally, the relationships between en-vironmental factors, water masses, and, in particular, zooplankton were explored. The results revealed that zooplankton abundances were 337.35 ind/m3, 280.01 ind/m3, 4.32 ind/m3, and 14.78 ind/m3 in the winter, spring, summer, and autumn, respectively. The zooplankton numbers between spring and summer, and between autumn and winter significantly changed, but remained steady between winter and spring, and summer between and autumn. The peak zooplankton abundance pe-riod in this water body was winter, which occurs a season before that in the East China Sea. In the investigation area, Evynnis cardinalis, an economically important fish species, exhibited obvious seasonal distribution characteristics：Capture rates in winter and spring were higher than those in summer and autumn, which was consistent with the seasonal variation characteristics of zooplankton. High quantities of zooplankton in the winter and spring provided sufficient food to supple-ment fish populations and therefore provide a valuable resource for fish reproduction and growth. Northwest Beibu Gulf is mainly affected by coastal water, offshore current and mixed water. Coastal water is composed of sea water and mixed water that is diluted by terrestrial runoff to the sea. A high salinity offshore current that is composed of offshore water runs into the Beibu Gulf from the bay mouth. Mixed water composed of coastal and offshore water converges in the continental shelf area. In the winter and spring, zooplankton distribution characteristics were similar;higher numbers of zooplankton were recorded in gulf and coastal waters than in inshore waters. However, zooplankton abundance in inshore waters was significantly higher than those in gulf and coastal waters during the summer and autumn. Sea water and mixed water in this area are affected by seasonal changes in coastal waters;the dominant species succession consisted of warm temperate neritic species in spring, warm water offshore species in summer and autumn, and warm water neritic species in winter. The dominant species were Penilia avirostris, Calanus sinicus, and Flaccisagitta enflata in the winter, spring, and summer and autumn, respec-tively. The ecological adaptability of the main dominant species determined the spatial and temporal distribution of these species, which in turn determined the zooplankton distribution characteristics. The combination of internal （ecological adaptation） and external （seasonal environmental change） factors resulted in the zooplankton distribution variation observed in this study. These factors also likely drove seasonal species succession in this area. Zooplankton are a vital food source for most fish species during their larval periods. Variations in zooplankton distribution and quantity can be either directly or indirectly affected by fish inges-tion, migratory and catch behavior, and feeding period. Fish egg and larval densities were 6.83 ind/m3, 3.09 ind/m3, 0.05 ind/m3, and 0.20 ind/m3 from winter to autumn;seasonal trends were highly consistent with those of zooplankton. A strong positive cor-relation indicates that rich food sources of zooplankton facilitate both fish egg and larval development.