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RESEARCH PRODUCT

Controlling factors of phytoplankton assemblages in wetlands: an experimental approach

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The aim of this work is to answer some questions like: what factors control the phytoplankton assemblage? What factor or factors are perturbing the assemblage? What factors are driving or maintaining the stability? Are the different responses to the control factors dependent on the hierarchy level? For that, we tested experimentally the influence of herbivory, planktivory, nutrients and sediment on phytoplankton assemblages and its stability from a hypertrophic wetland (Las Tablas de Daimiel National Park, Spain) in three microcosm experiments. The study of the steady state phytoplankton assemblages in this perturbed system could point out some underlying processes instead of competition. The presence of planktivorous fish and the different composition of zooplankton have minor importance in phytoplankton composition. Conversely, sediment is of paramount importance, promoting a more diverse phytoplankton assemblage. When sediment or nutrient pulses are absent, phytoplankton become dominated by slow-growing algae, present but not dominant in the studied wetland community. We suggest that alternate states of phytoplankton assemblages in a eutrophic wetland occur as a sequence of substitutions persistently altered by perturbations, thanks to the close coupling with sediment, and that possibly trophic relationships are irrelevant.