Interspecific Resource Competition—Combined Effects of Radiation and Nutrient Limitation on Two Diazotrophic Filamentous Cyanobacteria

Abstract

The cyanobacterial blooms in the Baltic Sea are dominated by diazotrophic cyanobacteria, the potentially toxic species Aphanizomenon sp. and the toxic species Nodularia spumigena. The seasonal succession with peaks of Aphanizomenon sp., followed by peaks of N. spumigena, has been explained by the species-specific niches of the two species. In a three-factorial outdoor experiment, we tested if nutrient and radiation conditions may impact physiological and biochemical responses of N. spumigena and Aphanizomenon sp. in the presence or absence of the other species. The two nutrient treatments were f/2 medium without NO (3) (-) (-N) and f/2 medium without PO (4) (3-) (-P), and the two ambient radiation treatments were photosynthetic active radiation >395 nm (PAR) and PAR + UV-A + UV-B >295 nm. The study showed that Aphanizomenon sp. was not negatively affected by the presence of N. spumigena and that N. spumigena was better adapted to both N and P limitation in interaction with ultraviolet radiation (UVR, 280-400 nm). In the Baltic Sea, these physical conditions are likely to prevail in the surface water during summer. Interestingly, the specific growth rate of N. spumigena was stimulated by the presence of Aphanizomenon sp. We suggest that the seasonal succession, with peaks of Aphanizomenon sp. followed by peaks of N. spumigena, is a result from species-specific preferences of environmental conditions and/or stimulation by Aphanizomenon sp. rather than an allelopathic effect of N. spumigena. The results from our study, together with a predicted stronger stratification due to effects of climate change in the Baltic Sea with increased temperature and increased precipitation and increased UV-B due to ozone losses, reflect a scenario with a continuing future dominance of the toxic N. spumigena.

Occurrence of cyanobacteria and cyanotoxin in the Southern Baltic Proper. Filamentous cyanobacteria versus single-celled picocyanobacteria

“…The fluctuations in cyanobacterial structure and abundance are regulated by the concentration of nutrients, thermal stratification of water masses, weather-induced water mixing or upwelling events (Laamanen & Kuosa, 2005;Vahtera et al, 2005;Laanemets et al, 2006;Vahtera et al, 2007;Nausch et al, 2008;Mohlin et al, 2011). In our studies, the heterogenic character of cyanobacterial occurrence in the Southern Baltic Proper was documented.…”

Impact of temperature and species interaction on filamentous cyanobacteria may be more important than salinity and increased pCO2 levels

“…1]. For Aphanizomenon sp., assuming a cell volume of 8.9 9 10 -8 mm 3 (Mohlin et al 2012), initial cell numbers were 6.3 9 10 7 for monocultures and 5.2 9 10 7 cells L -1 for mixed cultures. For N. spumigena, assuming a cell volume of 23.6 9 10 -8 mm 3 (Mohlin et al 2012), initial cell numbers were 4.0 9 10 7 and 3.4 9 10 7 cells L -1 , for monocultures and mixed cultures, respectively.…”

“…Moreover, a stagnant water column will expose the species in the euphotic zone to high intensities of ambient radiation. N. spumigena continues to grow under both nutrient deficiency and high ambient radiation intensities (Mohlin and Wulff 2009;Pattanaik et al 2010;Mohlin et al 2012). Furthermore, the stabilization of the water column in association with increasing temperatures may cause the spring bloom to begin earlier (Hagström and Larsson 1984) and potentially also the cyanobacteria bloom.…”

Cyanobacteria in Scandinavian coastal waters — A potential source for biofuels and fatty acids?

“…spumigena had continuously positive specific growth rate in all treatments throughout the experiment (data not shown). N. spumigena generally has higher specific growth rate than A. flos-aquae ( [73], Wulff et al, unpublished). This may be a competitive advantage, allowing N. spumigena to reach and maintain high biovolume and cell concentration during the bloom.…”

“…1, Table A.1). The higher biovolume for N. spumigena, compared to A. flos-aquae and D. lemmermannii in all treatments on both Day 7 and Day 14, may also be due to N. spumigena high irradiance tolerance [64,72,73]. During the summer-blooms in the Baltic Sea, N. spumigena is distributed in the top 5 m of the water column, Anabaena sp.…”