AME 46:125-140 (2007)  -  doi:10.3354/ame046125

Effects of nutrient enrichment on Prymnesium parvum population dynamics and toxicity: results from field experiments, Lake Possum Kingdom, USA

Daniel L. Roelke1,2,*, Reagan M. Errera1, Richard Kiesling3, Bryan W. Brooks4, James P. Grover5, Leslie Schwierzke1, Fabiola Ureña-Boeck4, Jason Baker5, James L. Pinckney6

1Department of Wildlife and Fisheries Sciences, and 2Department of Oceanography, Texas A&M University, 2258 TAMUS, College Station, Texas 77843-2258, USA
3Environmental Science Institute, University of Texas at Austin, and US Geological Survey, 8027 Exchange Drive, Austin, Texas 78754-4733, USA
4Department of Environmental Studies, and Center for Reservoir and Aquatic Systems Research, Baylor University, One Bear Place #97266, Waco, Texas 76798, USA
5Department of Biology, and Program in Environmental and Earth Sciences, University of Texas at Arlington, Box 19498, Arlington, Texas 76019, USA
6Marine Science Program and Department of Biological Sciences, University of South Carolina, Columbia, South Carolina 29208, USA

ABSTRACT: Large fish kills associated with toxic populations of the haptophyte Prymnesium parvum occur worldwide. In the past 5 yr, incidences of P. parvum blooms in inland water bodies of Texas (USA) have increased dramatically, where cell densities in excess of 1 × 107 cells l–1 are typically observed. We conducted field experiments (Lake Possum Kingdom) during the fall and early spring of 28 d duration using 24 enclosures of 1.57 m3 each. The experiments investigated the effect of nutrient enrichment, immigration of P. parvum and addition of barley straw extract on phytoplankton biomass and assemblage structure, P. parvum population density, zooplankton biomass and assemblage structure, bacteria, and toxicity. Nutrient enrichment stimulated P. parvum population growth beyond bloom proportions (>1 × 107 cells l–1). However, P. parvum did not dominate the assemblage under these conditions, as it does during natural blooms. Instead, euglenophytes and chlorophytes dominated. Toxicity, estimated using fish (Pimephales promelas) and cladoceran (Daphnia magna) bioassays and which is linked to P. parvum’s allelopathic and mixotrophic effectiveness, was greatly reduced (eliminated in many cases) under conditions of nutrient enrichment. The suppression of toxicity by nutrient addition suggested that targeted and time-limited nutrient manipulations might be used to mitigate the effects of P. parvum blooms. Immigration of P. parvum into natural assemblages and addition of barley straw extract had no significant effect on plankton dynamics.

KEY WORDS: Harmful algal bloom · HAB · Management · Mitigation · Immigration · Barley straw extract

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