Eutrophication-induced changes in benthic algae affect the behaviour and fitness of the marine amphipod Gammarus locusta
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Kraufvelin P, Salovius S, Christie H, Moy FE, Karez R, Pedersen MF
coastal eutrophication, nutrient enrichment, Rocky shore, mesocosm, grazing, Plant–animal interaction, Oslofjord, Solbergstrand, Norway, 12 m3
This study, conducted in mesocosms, natural field sites, and in laboratory aquaria, showed that eutrophication altered the nutrient status anddominance patterns among marine macroalgae, which in turn, stimulated gammaridean density. Gammaridean abundance correlated positivelywith both nutrient addition and the amount of green algae (also stimulated by nutrient enrichment). Path analysis indicated that the direct effect ofnutrients on gammaridean density was of less importance than the indirect effect through increased production of green algae. In cage colonisationexperiments, either in the field or in a control mesocosm kept under ambient nutrient conditions, more gammarids colonised nutrient enriched algae(E-algae) than algae with ambient nutrient levels (A-algae). Gammarus locusta generally grew faster on nutrient enriched algal specimens andwhen reared on green rather than on brown algae (fucoids). The nutrient status of periphytic algae did not affect gammaridean growth significantly,but the number of egg-carrying females (and thus egg production) was significantly higher among gammarids reared on E-periphyton. Thegammaridean habitat preference order (red > green > brown > periphyton) was almost the reverse of their growth rate in feeding assays(periphyton > green > brown). This implies that macroalgae may be more important as a habitat than as a food source for these animals, whichthen have to become mobile in search of optimal food items. In this process, algal nutrient content was important as the gammarids in our studyactively chose high quality nutrient-rich food, which, in addition, increased their fitness. Stimulated growth rates and egg production mayultimately lead to population increase, which, combined with the preference for high nutrient food items may dampen the initial effect of nutrientenrichment (i.e. blooms of green macroalgae) in shallow coastal waters.# 2005 Elsevier B.V. All rights reserved.
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