长江口几种优势桡足类对微型浮游动物的摄食研究

PREDATION OF SEVERAL DOMINANT COPEPODS ON MICROZOOPLANKTON IN CHANGJIANG RIVER ESTUARY

利用现场海水培养实验,结合浮游动物网样数据,研究长江口邻近海域几种优势桡足类(中华哲水蚤、背针胸刺水蚤、太平洋纺锤水蚤和精致真刺水蚤)对微型浮游动物的摄食影响。结果表明,精致真刺水蚤虽然属于肉食性种类,但几乎不摄食微型浮游动物;其余三种杂食性桡足类中华哲水蚤、背针胸刺水蚤和太平洋纺锤水蚤对微型浮游动物(纤毛虫+异养甲藻)的摄食率分别为0.66、0.09和0.59μg C/(ind·d),分别占其日总摄食量的29%、24%和37%。其中,异养甲藻在初始生物量和对桡足类饵料贡献上分别占整个微型浮游动物的30%和28%,是微型浮游动物中一个重要的组成类群。中华哲水蚤对微型浮游动物的摄食率与初始食物浓度有显著的正相关关系,并且对体长>20μm纤毛虫的清滤率要明显高于对体长<20μm的纤毛虫(P<0.01)的清滤率,表明其偏好摄食较大个体的食物。通过Chesson选择性指数显示,尽管微型浮游动物在生物量上远小于浮游植物,但桡足类能优先选择摄食微型浮游动物;进一步结合网采浮游动物数据,获得各站三种优势桡足类丰度平均占桡足类总丰度的77%,但它们对微型浮游动物现存生物量的摄食压力仅为0.8%,表明桡足类对微型浮游动物群落的下行控制作用并不明显,仍有大部分微型浮游动物生物量未通过摄食途径进入到桡足类群落中。

Predation of four dominant copepods(Calanus sinicus, Centropages dorsispinatus, Acartia pacifica, and Euchaeta concinna) on microzooplankton was estimated in Changjiang(Yangtze) River estuary and adjacent waters by in-situ incubation. E. concinna hardly fed on microzooplankton although it is a carnivorous species, and for other three species(C. sinicus, C. dorsispinatus, and A. pacifica), the ingestion rate on microzooplankton(ciliate + heterotrophic dinoflagellate) reached 0.66, 0.09, and 0.59 μg C/(ind·d), accounting for 29%, 24%, and 37% of daily carbon intake of copepod on average, respectively. Heterotrophic dinoflagellate, as an important component of microzooplankton, contributed 30% biomass and 28% food intake of microzooplankton. The correlation between the ingestion rate of C. sinicus and the initial concentration of microzooplankton was significantly positive, and the clearance rate on > 20 μm ciliate was significantly higher than <20 μm individuals(P<0.01), indicating its preferences to larger individuals. Although the biomass of microzooplankton was much less than that of phytoplankton, copepods preferred to feed on microzooplankton, as indicated by the Chesson's Index of selectivity. The three dominant species accounted for 77% of total abundance of copepod community on average, but they could remove just 0.8% of the microzooplankton standing stock daily. Therefore, the top-down effect by copepod on microzooplankton community is insignificant, and most microzooplankton biomass do not enter copepod community via predation.