Springer Online Journal Archives 1860-2000
Abstract The zoobenthos communities within the littoral zones of five low alkalinity, Ontario lakes were examined during summer 1987. Detached algal clouds or metaphyton, dominated by algae from the family Zygnemataceae, accumulated over the summer in three of these lakes. Previous researchers have hypothesized that diminished grazing pressure due to extirpation of acid sensitive herbivores might enhance the development of metaphytic algae at pHs less than 6. No overt consistent differences existed among the abundances of small (cladocerans, cyclopoids, ostracods, oligochaetes, dipterans) or medium (amphipods, gastropods, emphemeropterans, trichopterans) grazers in study lakes with or without metaphyton. Notable differences did exist, however, with respect to what we term large grazers. Crayfish, algivorous fish (mostly cyprinids), and to a lesser extent tadpoles, were absent or rare in the three lakes with metaphytic algae but abundant in those without. If a reduction in grazing pressure can be implicated as a factor in enhanced metaphyton development, our correlative results suggest that it is the large grazers, particularly crayfish, that are the most likely candidates.
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