浮游动物诱发藻类群体的形成

从研究蓝藻水华形成机理的需要出发,综述了浮游动物的牧食压力对藻类群体形成的诱发作用。指出诱发藻类群体形成的化合物来自牧食性浮游动物对藻类的有效牧食,是藻类群体形成的重要原因之一,而这些诱发性的化合物并不是有关生物体的组成成分,是种间相互作用的结果。藻类群体的形成方式有源于一个母细胞的分裂和业已存在的单细胞的聚合两种方式,栅藻的诱发性群体可能是来自一个母细胞的分裂,而在其它藻类的诱发性群体形成如铜绿微囊藻则可能是业已存在的单细胞的聚合。由于藻类形成群体后能显著降低浮游动物对其牧食速率,因此,这种诱发性群体形成的现象,可以解释为藻类对变化的牧食压力的一种有效的反牧食防御策略,也是两者协同进化的结果。浮游动物对藻类群体形成的重要作用,在研究模拟蓝藻群体及水华形成值得借鉴应用。作者还提出推测,水华蓝藻的群体形成,可能就是在富营养化条件下藻类快速生长,加上浮游动物的牧食压力共同作用下联合驱动的结果,而这种群体形成很可能在积累到一定程度后,结合特定的气象水文等理化因子,就会聚集于水表“爆发”出肉眼可见的水华。因此,开展浮游动物牧食作用对水华蓝藻早期群体形成诱发效应的研究不仅能加深对水华形成的全面认识,而且对于进一步认识藻类的诱发性反牧食防御适应机制、揭示生态系统中生物之间的复杂关系也具有重要的理论意义。

Effects of zooplankton grazing on colony formation in algae: A review

In order to understand the mechanisms of bloom formation in cyanobacteria (blue-green algae), we reviewed the literature on inducing effects of grazing pressure of zooplankton on colony formation in algae. These published studies demonstrated that effect of colony-inducing compounds released by herbivorous zooplankton is a key factor in colony formation of algae. The inducing chemicals are not the functional constituents of the organisms involved but the result of the interaction between species. Probably two different mechanisms are involved in the colony formation. One mechanism such as in Scenedesmus spp., is that colonies are formed when daughter cells of a recently divided cell fail to separate during reproduction, the other is that colonies are formed through adhesion of already existing single cells, such as in Microcystis aeruginosa. Because a high proportion of colonies could significantly reduce the grazing rate of zooplankton, algal colony formation may be interpreted as an induced defense strategy against grazing to pare down mortality due to animal grazing. If colony formation in cyanobacteria is induced by the grazing pressure in eutrophic waters then visible blooms will occur when colonies accumulate to certain magnitudes under favorable hydrometeorological conditions. It is therefore important to conduct research on the early stage of colony formation in cyanobacteria induced by grazing pressure of herbivorous zooplankton to understand the bloom formation and to provide insights into the adaptive mechanisms of inducing defense against grazing in algae as one of the complex interactions among organisms in aquatic ecosystems.