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

• 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 similar to 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 concentration-dependent 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.

Subject headings

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Oceanografi, hydrologi och vattenresurser (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Oceanography, Hydrology and Water Resources (hsv//eng)

Keyword

Algae

Allelopathy

Grazers

Molecular diet analysis

Nodularin

Toxic cyanobacteria

Trophic interactions

Marine Ecology

marin ekologi

Publication and Content Type

ref (subject category)

art (subject category)