中肋骨条藻-裸甲藻-双毛纺锤水蚤营养传递的级联效应

中型浮游动物因摄食微型浮游动物,释放了微型浮游动物对浮游植物的摄食压力,这种营养级联效应会增加浮游植物丰度和降低中型浮游动物对浮游植物的摄食率,从而弱化浮游生物网营养传递过程中的下行控制作用。本研究在实验室模拟了食物链中肋骨条藻-裸甲藻-双毛纺锤水蚤的营养传递过程,发现在中肋骨条藻低生物量时,双毛纺锤水蚤偏好于选择摄食裸甲藻;高生物量时,双毛纺锤水蚤偏好选择摄食中肋骨条藻。营养传递过程中存在正的级联效应(0.018~0.12 d^-1),级联效应的大小与裸甲藻的摄食率和双毛纺锤水蚤对裸甲藻的摄食选择指数呈现显著的正相关关系。双毛纺锤水蚤对中肋骨条藻的直接摄食死亡率大于营养级联效应,从而导致中肋骨条藻生物量的降低。因此,营养级联效应对中型浮游动物摄食浮游植物的影响要弱于中型浮游动物的直接摄食作用。

Trophic cascading effect on the food chain of Skeletonema costatum-Gymnodinium sp.-Acartia bifilosa

Trophic cascading occurs during the release of the grazing pressure on phytoplankton from microzooplankton owing to the grazing of mesozooplankton on microzooplankton. This may result in an increase in the abundance of phytoplankton, thereby causing a decrease in ingestion, weakening the transmission of the top-down control from mesozooplankton to phytoplankton in the pelagic foodweb. In this study, we simulated a food chain involving Skeletonema costatum-Gymnodinium sp.-Acartia bifilosa under laboratory conditions to quantify the trophic cascade effect and feeding impact on phytoplankton. The results showed that Acartia bifilosa fed selectively on the Gymnodinium sp. under low Skeletonema costatum biomass; in contrast, Skeletonema costatum had its feeding under high diatom biomass. There was a positive effect on the trophic cascades (within the range of 0.018~0.12 d^-1) in the trophic transmission. The strength of the trophic cascade had a significant positive correlation on the grazing rate of Gymnodinium sp. on diatom and feeding selectivity index of Acartia bifilosa on dinoflagellate. The direct grazing mortality on Skeletonema costatum by Acartia bifilosa was higher than the positive effect of trophic cascades; this in turn lead to the decrease in Skeletonema costatum biomass. Therefore, the influence of the trophic cascade effect was weaker than that of direct feeding on phytoplankton by mesozooplankton.