ARE BLUE-GREEN-ALGAE A SUITABLE FOOD FOR ZOOPLANKTON - AN OVERVIEW

One of the reasons suggested to explain the dominance of blue-greens in eutrophic lakes is that they are not used as food by zooplankton; and even when ingested, they are poorly utilized. An increase in herbivores might be the expected result of biomanipulation of the aquatic food chain. This attempt at controlling the algae population is, however, destined to fail if zooplankton do not also utilize blue-greens as food. In this respect, a series of in-lake experimental results indicates that after the food chain has been biomanipulated, there is a decrease in blue-green density in periods when there is an increase in herbivores. Is this only an accidental result or are the two facts interrelated; in other words, can the decrease in the density of blue-greens be attributed to the increased use of them by zooplankton herbivores? The suitability of blue-greens as food for zooplankton has been widely investigated by many authors with contrasting and inconclusive results. Two main factors seem to play important role in determining their suitability as food: the biochemical properties of the different species, or even different strains of the same species; and the shape and size of the colonies. In particular, biochemical properties can result in toxic effects on zooplankton, while size and shape may strongly interfere with filtering, thus reducing the possibility of gathering food. © 1990 Kluwer Academic Publishers.