Abstract
Cyanobacterial blooms are the most important and best studied type of harmful algal blooms in fresh waters and brackish coastal seas. We here review how and to which extent they resist grazing by zooplankton, how zooplankton responds to cyanobacterial blooms and how these effects are further transmitted to fish. Size, toxicity and poor nutritional value are widespread mechanisms of grazing defense by cyanobacteria. In some cases, defenses are inducible, in some they are obligate. However, to some extent zooplankton overcome grazing resistance, partly after evolutionary adaptation. Cyanotoxins are also harmful to fish and may cause fish kills. However, some fish species feed on Cyanobacteria, are able to reduce their abundance, and grow on a cyanobacterial diet. While reduced edibility for crustacean zooplankton tends to elongate the food chain from primary producers to fish, direct feeding by fish tends to shorten it. The few available comparative studies relating fish yield to nutrients or phytoplankton provide no indication that cyanobacteria should reduce the ratio fish production: primary production.
Highlights
Blooms of large colonial or filamentous Cyanobacteria are the most important and best studied type of harmful algal blooms (HABs) of freshwaters and brackish coastal seas
We examine the literature about edibility for zooplankton and the extent to which colony size, toxicity, and poor nutritional value protect cyanobacteria from grazing by zooplankton and how these mechanisms impact the growth and survivorship of zooplankton
We examine the interactions between Cyanobacteria and fish, beginning with the impact of cyanotoxins on fish with a focus on fish kills ascribed to Cyanobacteria, while the
Summary
Blooms of large colonial or filamentous Cyanobacteria are the most important and best studied type of harmful algal blooms (HABs) of freshwaters and brackish coastal seas. The relationship of cyanobacterial HABs is double-faced, by being a symptom of water quality deterioration and by further deteriorating water quality [2] These deteriorating effects include the production of bad odors and toxicity for humans and livestock, oxygen depletion by decaying accumulations of biomass and by alterations of the pelagic food web because of their poor edibility for zooplankton [1]. We examine the literature about edibility for zooplankton and the extent to which colony size, toxicity, and poor nutritional value protect cyanobacteria from grazing by zooplankton and how these mechanisms impact the growth and survivorship of zooplankton. Question of a potential top-down control of Cyanobacteria by fish and the possibility of fish to grow on a cyanobacterial diet
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