洱海浮游桡足类群落结构对季节性休渔的响应

为了解洱海浮游桡足类群落结构的季节动态特征,于2009年2~11月对洱海浮游桡足类进行逐月采样.结果显示:洱海浮游桡足类生物量的季节性分布呈"双峰型",峰值分别出现在休渔期中期和捕鱼期中期.在休渔期中期,桡足类以杂食性的剑水蚤Mesocyclops dissimilis为优势种;在捕鱼期中期,则以滤食性的哲水蚤舌状叶镖水蚤为优势种.季节性休渔不仅导致鱼类对桡足类的捕食压力出现季节性变化,而且通过影响枝角类的群落结构,改变枝角类对桡足类的竞争压力.在相对较低的捕食压力和较大的食物竞争压力影响下,桡足类以杂食性的剑水蚤为优势类群;在相对较大的捕食压力和较低的食物竞争压力下,以滤食性的哲水蚤为优势类群.

Response of Planktonic Copepods to Seasonal Fishing Moratorium in Erhai Lake, Yunnan, China

Copepods were sampled monthly from February to November in 2009 in a subtropical plateau lake,Erhai,Yunnan,China,in which a moratorium on spring and early summer fishing was imposed by local government,in order to investigate the seasonal dynamics of Copepod community.The biomass of Copepods showed a bimodal seasonal distribution,the first peak in the mid fishing moratorium and the second peak in the mid fishing season.The omnivorous cyclopoid Mesocyclops dissimilis was dominated in the mid fishing moratorium,while a filter-feeding calanoid Phyllodiaptomus tunguidus was dominated in the mid fishing season.The seasonal fishing moratorium affected not only the predation pressure from fish on copepods,but also changed the competitive pressure from Cladocera on copepods by influencing the community structure of Cladocera.Under low predation pressure but high food-competitive pressure,the dominant species of copepods were omnivorous cyclopoids,while under high predation pressure and low food-competitive pressure,the filter-feeding calanoid took over in dominance.