Effects of Microcystis aeruginosa on interference competition between Daphnia pulex and Keratella cochlearis

Abstract

Laboratory experiments tested the hypothesis that a toxic strain of Microcystis aeruginosa decreases the ability of Daphnia pulex to interfere with Keratella cochlearis . To test a variety of conditions, juvenile and adult Daphnia were exposed to the cyanobacterium for different time periods prior to, and during the experiments . Adult Daphnia not only suppressed rotifers over successive two-day intervals, but also had a significant impact within a 24-hour period . However, the presence of Microcystis (5 x 105 cells ml -1 ) decreased the Daphnia effect in both experiments . Although juvenile Daphnia also significantly suppressed Keratella population growth, the presence of Microcystis (10 5 and 5 x 10 5 cells ml -1 ) caused a significant reduction in daphniid body size and decreased the ability of both nonacclimated and acclimated daphniids to suppress rotifers . Keratella inhalation and mortality are positively correlated with filtering rates and body size of Daphnia . Therefore, the feeding rates and size structure of a Daphnia population will determine its potential to interfere with vulnerable rotifers . In all experiments the presence of Microcystis significantly decreased the ability of Daphnia to interfere with this rotifer despite the fact that Keratella was also inhibited. In the field this effect might be augmented if Microcystis colonies are more easily ingested by cladocerans than by the rotifers . 117

The role of cladocerans reflecting the trophic status of two large and shallow Estonian lakes

“…The cladoceran data from L. Peipsi and in L. Võ rtsjä rv (Table 2, 3; Fig 3) suggest that cladocerans consume more algae in L. Peipsi than in L. Võ rtsjä rv. The food ration of cladocerans is determined directly by mean cladoceran weight; feeding efficiency is proportional to body size (Carpenter & Kitchell, 1992;Sartonov, 1995). Correlation analysis has revealed a positive relationship between mean cladoceran weight and grazing activity for both studied lakes (L. Peipsi: r = 0.6, L. Võ rtsjä rv: r = 0.4, P < 0.0001; Haberman & Nõ ges, 2003).…”

“…Dodson & Frey (2001) have found that most cladocerans prefer algae in the size range from 5 to 35 lm. The larger is the grazer, the more efficient is its grazing (Sartonov, 1995;Meijer et al, 1999).…”

The Rotifer Assemblage in a Shallow, Eutrophic Chinese Lake and Its Relationships with Cyanobacterial Blooms and Crustacean Zooplankton

“…There are several possible hypotheses for this. Firstly, large colonial or filamentous cyanobacteria may be too large for rotifers to ingest, and hence, the inhibitory effect of Microcystis aeruginosa endotoxin could be lessened (Gilbert 1990, Sartonov 1995. Secondly, in nature other potentially nutritious food sources are closely associated with M. aeruginosa colonies, including bacteria, protozoans (Paerl 1984b), and eukaryotic algae (Kilham et al 1986) which can be consumed by rotifers.…”

Different competitive outcomes among four species of cladocerans under different alga combinations of colonial Microcystis spp. and green alga Scenedesmus obliquus

“…Jungamnn, 1992;DeMott, 1999). Keratella cochlearis was superior in competition with D. pulex under toxic Microcystis (Sartonov, 1995). However, there is little or no evidence for lethal effects of toxic cyanobacteria on crustacean plankton in the field (Haney, 1987).…”

“…Many factors, including concentration, size, Microcystis toxin and alternative food abundance during blooms may result in zooplankton shifts (Jarvis et al, 1987;Fulton & Paerl, 1988;Sartonov, 1995;Chen & Xie, 2003, 2004. Different responses of species to these factors result in observed zooplankton community structure.…”