罗非鱼对微型生态系统浮游生物群落和初级生产力的影响

Effect of Nile tilapia on plankton community and primary productivity of freshwater microcosms.

本文报道罗非鱼不同放养密度对淡水微型生态系统结构与功能影响的部分研究结果。罗非鱼的捕食使微型生态系统中浮游动物密度下降,引起浮游植物密度、初级生产力和P/R系数的增长,同时使水柱透明度降低而pH值增高,以致于实验后期微型生态系统具有典型的富营养化水体的特征。就罗非鱼放养密度不同的微型生态系统而言,虽然其浮游生物密度和P/R系数存在显著的组(或部分组)间差异,但不同密度组的初级生产力水平和最终的理化状况相差不大,并且罗非鱼的收获量甚为接近。因此,实验条件下微型生态系统的群落结构和代谢的变化,按照营养级联假说不能很好地予以解释,表明微型生态系统是由捕食(下行影响)和理化因素(上行影响)共同调节或控制的。根据微型生态系统的实验结果推断,放养较大密度的罗非鱼,将会加速营养物负荷较高的天然水域富营养化的进程。

In this paper, the effect of varying densities of Nile tilapia, Oreochromis niloticus,on structure and function of freshwater microcosms is studied. The results show thatthe predation of Nile tilapia induces the decrease of zooplankton density and results in the increase of phytoplankton denslty,primary productivity and P/R ratio. In the meanwhile, the transparency of water column is decreased andits pH value is increased, which induces the water body of freshwater microcosms becoming eutrophic in the later period of experiment. There are significant differences in plankton densities and P/R ratios among all or part of the microcosms with tilapia, but their primary productivity, final physicochemical condition and fish harvest are about the same. Therefore, the changes of community structure and metabolism in microcosms under experimental conditions are not well consistent with the predictions from trophic cascade hypothesis ,indicating that the microcosms is regulated or controlled by both predation (top-down effect and physico-chemical factors (bottom -up effect). It is inferred that if stocking greater density of Nile tilapia, the eutrophication process of natural water body under greater nutrient loading will be speeded up.