Interrelations between Blue-green Algae and Zooplankton in Eutrophic Lakes-A Review

Abstract

Studies on interrelations between blue-green algae and zooplankton are reviewed, and the interrelations in eutrophic lakes are discussed.
Laboratory experiments have shown that several blue-green algae are toxic to zooplankton and reduce the feeding, assimilation, survival and growth rates of various zooplankters. The algal toxicity differs among algal species and among algal strains. Blue-green algae are considered to be nutritionally inadequate to zooplankton, even if they are non-toxic. In nature, however, the deleterious effects of blue-green algae are recognized only on large bodied cladocerans. In lakes where blue-green algae are blooming, the zooplankton community is usually dominated by small-bodied cladocerans, rotifers and copepods. They seem to have different mechanisms to coexist with the algal blooms ; i.e., inability to consume filamentous or large colonial blue-green algae (small-bodied cladoccerans), resistance to toxic chemicals of the algae (rotifers), avoidance of consumption of the algae by chemosensory feeding (cope-pods).
Zooplankters probably promote the dominance of filamentous or colonial blue-green algae by grazing on small edible algae which compete with blue-green algae for nutrients and by releasing nutrients obtained from these algae for use by the blue-green algae.
In eutrophic lakes, bloom forming blue-green algae are considered to be hardly ingested by zooplankton. The organic matters produced by the algae are probably utilized by zooplankton through bacteria which had grown in the process of the decomposition of the algae. Thus, the main path way of the organic matters from phytoplankton to zooplankton is detritus food-chain in these lakes.