A meso-predator release of stickleback promotes recruitment of macroalgae in the Baltic Sea |
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Authors: | Katrin Sieben Lars Ljunggren Ulf Bergström |
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Institution: | a Department of Marine Benthic Ecology & Evolution, Centre for Ecological & Evolutionary Studies, University of Groningen, PO Box 11103, 9700 CC Groningen, The Netherlandsb Swedish Board of Fisheries, Institute of Coastal Research, Skolgatan 6, S-742 42 Öregrund, Sweden |
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Abstract: | In the Baltic Sea, increased populations of the three-spined stickleback are invading the coastal zone in summer, following declines in large predatory fish such as cod, pike, and perch. Here, we explore the consequences of such a meso-predator release on a near-natural scale, by manipulating stickleback densities in four large 600 m2 enclosures: two ‘removal’ and two ‘addition’ enclosures. Higher densities of stickleback resulted in a three times higher recruitment of ephemeral green macroalgae. At the same time we found higher abundances of the dominating invertebrate grazers with lower stickleback densities: higher numbers of both amphipods and smaller gastropods were found in one stickleback ‘removal’ enclosure and higher numbers of large gastropods occurred in the other ‘removal’ enclosure. Grazer abundances also depended on the macrophyte species that dominated the enclosures. Nutrient enrichment had no statistically significant effect on algal recruitment, although the mean number of algal recruits was almost doubled under enriched conditions. Our results indicate that a meso-predator release of stickleback may dramatically shift coastal food web constitution towards increased abundances of ephemeral macroalgae through a trophic cascade. |
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Keywords: | Coastal management Eutrophication Grazers Large-scale experiment Piscivorous fish Trophic cascade |
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