Rotifers, the jelly plankton of freshwater
2007
Dumont, H. J. (Henri J)
Jelly plankton (gelata) is a rather fuzzy concept that I attempt to redefine and expand: gelata should have no exo or endoskeleton, have a water content of 92-98%, and should usually be somewhat transparent. Although gelata are usually considered as part of the plankton, there are many cases in which they lead a benthic life, permanently or during part of their life. Gelatinous material can be part of the body, or can be secreted to form a sheath around it, especially in freshwater. Size is not a criterion: gelata individuals or colonies can be from 50 μm to 30 m and more in size. Early development stages (eggs and embryos) shed freely in the environment are not considered true gelata, even if enveloped in jelly. Under these conditions, jelly plankton in freshwater is represented by 20-40 species of cnidarians, by a few rhabdocoelid flatworms, and by up to 200 rotifer species (600+ if the periphytic and benthic species are included, and almost 1,500 species if males are included). Contrary to the ocean, where overfishing will benefit gelata, overfishing in freshwater will favor planktonic crustaceans, and these, in turn competitively suppress rotifers.
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