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Marine Ecology Progress Series

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MEPS 461:47-57 (2012)  -  DOI:

Environmental controls on the nitrogen-fixing cyanobacterium Nodularia spumigena in a temperate lagoon system in SE Australia

Daryl P. Holland1,*, Iris van Erp2, John Beardall1, Perran L. M. Cook3

1School of Biological Sciences, Monash University, 3800 Clayton, Victoria, Australia
2Department of Environmental Sciences, Aquatic Ecology and Water Quality Management Group, Wageningen University, PO Box 47, 6700 AA Wageningen, The Netherlands
3Water Studies Centre, Monash University, 3800 Clayton, Victoria, Australia

ABSTRACT: Estuarine blooms of N2-fixing cyanobacteria are rare, and the factors controlling them remain poorly understood outside the Baltic Sea. We measured in situ physico-chemical conditions and undertook nutrient-addition bioassays and dilution-based grazing experiments fortnightly over the 2010 to 2011 Austral spring-summer-autumn, to evaluate the role of physical environmental drivers, grazing and macronutrients on the growth of Nodularia spumigena Mertens (hereafter Nodularia) in a temperate lagoon system (Gippsland Lakes, Australia). Nodularia appeared in late summer, following a period of warm weather (water temperature > 22°C), high solar exposure, calm conditions, relatively low salinity (<22) and low dissolved inorganic nitrogen (~0.4 µmol l−1). A major bloom did not eventuate. Bioassays indicated N limitation prior to Nodularia appearing, and P limitation after, while in situ nutrient concentrations indicated N limitation throughout. Nodularia grew rapidly (~0.4 d−1) in control bioassays (no nutrients added), whereas other phytoplankton taxa showed zero or negative growth. N addition caused significantly lower Nodularia growth, while other taxa had higher growth. P addition did not significantly enhance Nodularia growth. This suggests Nodularia was able to obtain P from the water column and from phytoplankton breakdown. A reduction in grazing pressure via dilution led to lower growth rates of Nodularia and higher growth rates of other phytoplankton taxa. This suggests that the grazers selectively consumed taxa other than Nodularia, and that grazing positively influences Nodularia growth in this system. These data indicate that Nodularia growth was limited in situ by physical conditions (primarily solar radiation) and that nutrients and grazing were of second order importance.

KEY WORDS: Nodularia spumigena · Nutrient limitation · Grazing · Bioassay

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Cite this article as: Holland DP, van Erp I, Beardall J, Cook PLM (2012) Environmental controls on the nitrogen-fixing cyanobacterium Nodularia spumigena in a temperate lagoon system in SE Australia. Mar Ecol Prog Ser 461:47-57.

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