Toxin-producing cyanobacterium Nodularia spumigena, potential competitors and grazers: testing mechanisms of reciprocal interactions

Abstract

Interactions among toxic cyanobacteria, sympatric algae and planktivorous grazers are key processes governing plankton dynamics and cyanobacterial blooms. We studied interactions between the cyanobacterium Nodularia spumigena and microalgae (Rhodomonas salina and Tetraselmis suecica) as well as effects of zooplankton (copepod Eurytemora affinis) grazing on these interactions. N. spumigena was incubated without algae or with algae at different concentrations and with or without copepods. Following ~24 h incubation, we assayed changes in N. spumigena and algae abundance, concentration of intracellular (IC) and dissolved nodularin (toxin produced by N. spumigena) and quantity of Nodularia DNA in copepod guts (as a proxy for grazing pressure on the cyanobacterium). In the presence of algae, IC nodularin levels increased in a concentrationdependent manner; however, when copepods were present in the mixtures of algae and cyanobacterium, this increase was significantly less. The presence of T. suecica negatively affected the growth rate of N. spumigena, whereas the presence of the cyanobacterium strongly impeded growth of R. salina, but not of T. suecica. The IC nodularin quota correlated negatively with growth of R. salina, implicating the toxin's involvement in the observed growth suppression of the eukaryotic alga. Copepods actively ingested N. spumigena, even when the alternative food was plentiful, and neither N. spumigena quantity nor its toxin concentrations influenced copepod feeding rates and survival. These findings suggest complex allelopathic interactions between the autotrophs, whereas mesozooplankton grazers have an indirect negative effect on the nodularin concentrations by suppressing the competitors. These findings underscore the need to study ecologically important interactions among toxic cyanobacteria, sympatric algae and grazers, if we are to understand mechanisms regulating cyanobacterial blooms.

Does the presence of zooplankton influence growth and toxin production ofNodularia spumigena?

“…The growth rates observed in the current study are lower than previously reported for this species (e.g. ), but of equivalent magnitude as previously reported for this strain when grown in similar conditions . Although, there was a significant interaction effect of zooplankton taxa and density on N. spumigena biomass (Table ; Fig.…”

Incorporation of diazotrophic fixed N2 by mesozooplankton — Case studies in the southern Baltic Sea

“…In some studies consumer control of heterocystic cyanobacteria blooms is effective, but not others. Thus, there are contradicting findings on avoidance of filamentous cyanobacteria by A. bifilosa and Eurytemora affinis (Engström et al, 2000;Sellner et al, 1996) and active grazing by the latter on the other hand (Engström-Öst et al, 2011;Kozlowsky-Suzuki et al, 2003). The poor food quality of cyanobacteria has been attributed to the absence of long-chain polyunsaturated fatty acids (PUFAs, Gugger et al, 2002) and sterols (Summons et al, 2006;Volkman, 2003).…”

“…O'Neil and Roman, 1994), while Baltic Sea mesozooplankton usually avoids grazing of filaments (e.g. Engström et al, 2000;Engström-Öst et al, 2011;Sellner et al, 1996). It has been shown that Anabaena can have a strong inhibitory effect on zooplankton species (e.g.…”

Deciphering the biochemical spectrum of novel cyanobacterium-based biofilms for use as inoculants

“…The trophic structure of food webs in several aquatic systems indicates that cyanobacteria serve as a food source for the entire plankton community, and toxic cyanobacteria can have diverse effects on the speciation of macro/microfaunal populations in such environments (Capper et al 2006;Fyda et al 2009Fyda et al , 2010Engstrom-Ost et al 2011). With regard to aquatic ecosystems, including waterlogged paddy soil, it is well known that development of zooplankton populations, especially those of cladocerans, copepods, gastropods and rotifiers, prevents the establishment of algal blooms, especially in the first weeks of crop growth (Grant et al 1983(Grant et al , 1985Roger et al 1993).…”