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The relative importance of top‐down and bottom‐up control of phytoplankton in a shallow macrophyte‐dominated lake
Author(s) -
Stephen Debbie
Publication year - 1998
Publication title -
freshwater biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.297
H-Index - 156
eISSN - 1365-2427
pISSN - 0046-5070
DOI - 10.1046/j.1365-2427.1998.00321.x
Subject(s) - macrophyte , zooplankton , phytoplankton , environmental science , biomass (ecology) , mesocosm , eutrophication , ecology , biomanipulation , pelagic zone , plankton , aquatic plant , nitrate , biology , nutrient
1. Mechanisms stabilizing the plant‐dominated clear‐water state were investigated in Little Mere, U.K. Replicated, factorial, mesocosm experiments, carried out in 1995 and 1996, were designed to investigate the relative importance of top‐down (zooplankton grazing) and bottom‐up (nitrogen‐limitation) control in limiting algal growth, and the role of macrophytes in these processes. Treatments included increased salinity (1995) and sticklebacks (1996) to reduce zooplankton numbers, weekly nitrate additions and removal of macrophytes. 2. Contrary to the results of other studies, submerged plants did not reduce nitrate concentrations. Owing to the high stickleback density in the enclosures with fish, macrophytes did not provide a refuge for zooplankton during the experiment. In Little Mere, however, where fish densities are lower, macrophytes probably play a key role in maintaining clear water by providing refuge for pelagic zooplankton and habitat for attached Cladocera. 3. Phytoplankton in Little Mere was not nitrogen‐ (N) limited during the growing season. Although nitrogen availability sets a maximum potential phytoplankton biomass it was not realized owing to control by zooplankton grazing.