Initial conditions mediate the interaction between Daphnia and bloom‐forming cyanobacteria

Abstract

To assess whether Daphnia populations in eutrophic lakes can increase when bloom-forming cyanobacteria dominate the phytoplankton assemblage and whether such an increase can result in strong suppression of phytoplankton biomass, I created contrasting initial conditions (high Daphnia pulicaria, low cyanobacteria vs. low D. pulicaria, high cyanobacteria) via fish manipulation in large enclosures, then removed fish from some enclosures and subsequently monitored zooplankton and phytoplankton abundance for 48 days. After being released from fish predation, D. pulicaria was apparently able to reduce cyanobacteria and total phytoplankton biomass to very low levels despite the fact that the phytoplankton assemblage was initially composed of about 90% Microcystis aeruginosa, a species that has inhibited Daphnia growth and reproduction in many laboratory studies. Thus, it appears possible for Daphnia to graze down an established bloom of cyanobacteria. In contrast, in enclosures where fish were never present, M. aeruginosa was eventually able to increase from low levels despite initially high D. pulicaria biomass. As a result, the apparent effect of D. pulicaria on M. aeruginosa at the end of the experiment was very different across enclosures with different initial conditions.

Consequences of acclimation to Microcystis on the selective feeding behavior of the calanoid copepod Eudiaptomus gracilis

“…Selective feeders are not expected to reduce blooms and may even indirectly facilitate them, while large and physiologically adapted cladocerans may reduce blooms in certain cases (Rondel et al 2007;Sarnelle 2007;Wang et al 2010). However, the lack of observations monitoring zooplankton adaptations and tolerance over longer time scales limits predicting bloom-dominated plankton dynamics.…”

“…Further, the current results show that assuming a constant species-specific feeding behavior during extended cyanobacteria blooms is a misrepresentation of zooplankton. Such adaptive responses and subsequent changes in long-term tolerance may explain the contrasting effects observed between zooplankton and cyanobacteria in nature (Ghadouani et al 2003;Sarnelle 2007). Thus, zooplankton grazing on cyanobacteria must be viewed as a flexible and adaptive trait that likely affects species-specific tolerance.…”

“…Previous exposure to Microcystis can increase zooplankton tolerance to cyanobacteria under both natural and laboratory conditions (Gustafsson and Hansson 2004;Sarnelle and Wilson 2005;Ger et al 2010b). Better tolerance could be from adaptations in feeding behavior or physiological change resulting in reduced detoxification costs (DeMott et al 1991;Kozlowski-Suzuki et al 2003).…”

“…The extent of zooplankton grazing on cyanobacteria has consequences for the bloom dynamics and the stability of plankton communities and, thus, has long been recognized as central for efforts to control algal blooms through top-down trophic cascades (Sarnelle and Wilson 2005;Rondel et al 2007;Wang et al 2010). However, toxicity from ingesting cellular metabolites produced by cyanobacteria limits the potential for a significant grazing induced decline in blooms because it is the main cause of negative effects on zooplankton populations (Ghadouani et al 2003;Wilson et al 2006;Tillmanns et al 2008).…”

“…Most of the information about zooplankton-cyanobacteria interactions comes from cladocerans, which are characterized by relatively nonselective feeding on cyanobacteria and, subsequently, the potential to reduce blooms (Wilson et al 2006;Sarnelle 2007;Tillmanns et al 2008). Cladoceran-based generalizations restrict our understanding of plankton dynamics in bloom-dominated systems because cyanobacteria generally coexist with smaller and/or more selectively feeding zooplankton species such as copepods (Fulton and Paerl 1987;Koski et al 2002).…”