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Direct and indirect effects of grazing on the phytoplankton seasonal succession in an oligotrophic lake 总被引:2,自引:0,他引:2
Carrillo P.; Reche I.; Sanchez-Castillo P.; Cruz-Pizarro L. 《Journal of plankton research》1995,17(6):1363-1379
We examined the simultaneous dynamics of phytoplankton and zooplanktonin an oligotrophic lake, as well as the algal response to experimentalmanipulations of herbivore population structure and density.The seasonal succession of phytoplankton is characterized bya shift in dominance from eukaryotic species to prokaryoticcyanobacteria, as in a eutrophic lake. This unusual patternfor an oligotrophic lake is related to the release of zooplanktonphosphorus, rather than to the amount of total phosphorus. Thehighest estimated values of this released phosphorus occur duringthe co-dominance of small-sized species and of one calanoidpopulation, both under natural and experimental conditions.Our experimental results clearly reveal that a blue-green speciesreplaces non-blue-green ones when environmental conditions renderlow or intermediate values for released phosphorus, irrespectiveof the grazing pressure. The absence of predators or high levelsof released phosphorus stimulate non-blue-green growth. Theseresults agree with the successional pattern observed for thealgal assemblage under natural conditions. Nutrient recyclingplays an essential role in the maintenance of the metabolismof the pelagic system, and therefore the prevalence of a topdownregulation mechanism as proposed for such low-nutrient environmentsshould be reconsidered. 相似文献
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During August, 1987, we performed a series of Limnocorral experiments in lake La Caldera, a small winter-kill lake in which
phytoplankton is strikingly nutrient-limited. The effects of biomanipulation on zooplankton-phytoplankton relationships were
assessed by monitoring both individual species and whole-assemblage responses. Two sizes of enclosures were used (15 and 350
litres) and two treatments were assayed: 1) removal of zooplankton by 45 μm filter net and 2) doubling the natural grazing
pressure by increasing the zooplankton concentration. Results show the two enclosure types to differ strikingly: flagellates
disappeared from the small enclosures, resulting in four- to six-fold changes in chlorophylla concentration and three- to four-fold changes in number of individuals. Most species were grazed (a prey selectivity based
on criteria other than size was observed) and their net growth rate increased with zooplankton concentration, causing a net
increase in the phytoplankton growth, a stimulatory effect probably through nutrient regeneration that overrides the losses
due to grazing. 相似文献
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