Rooted floating-leaf macrophytes structure the coexistence of different phytoplankton assemblages within a shallow lake
Résumé
Aquatic macrophytes in shallow lakes control habitats through local turbulence, water transparency, nutrients and oxygen concentrations. As engineer species, they structure these ecosystems, increasing the biodiversity. While many studies focused on submerged macrophyte, research on habitats created by rooted floating-leaf macrophytes is scarcer. Macrophytes, such as water lilies, should have the similar ecological consequences as submerged macrophytes, but with greater shading. In this study, we showed how macrophytes structure phytoplankton assemblages and allow the coexistence of different assemblages in the same shallow lake. During summer 2018, we characterized the phytoplankton assemblages in 9 stations covered by water lilies and 6 stations in open water, in a large shallow water lake. The lake is colonized on a third of its surface by water lilies from April to October. We showed an effect of waterlilies on temperature, oxygen, pH, turbidity, phosphates and dissolved silicon. Many taxa of phytoplankton from almost all classes were in higher abundance in stations covered by macrophytes, while cyanobacteria showed a higher biomass and richness in open water. Unicellular mixotrophic flagellates predominated in macrophytes habitat, with all representatives of the classes Euglenophyceae and Cryptophyceae.
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