Microalgal and cyanobacterial assemblages on charophytes: a metacommunity perspective
Despite all of the studies that have been carried out on angiosperm macrophytes, it is still unknown beyond any doubt whether charophytes affect periphyton composition. From the viewpoint of aquatic community organization, we must not only answer this question but must also evaluate the importance of this source of periphyton to the seston. We will here discuss these topics from a metacommunity perspective, on which we base our two hypotheses. The first hypothesis is that periphytic assemblages are charophyte species-specific and hence that their metacommunity structuration also corresponds to niche-based paradigms (species sorting or mass-effect views). In this sense, patch (charophyte host)-dependent processes could explain the distribution of periphytic microalgae and cyanobacteria. It is known that dispersal is important because it allows compositional changes to track changes in local environmental conditions. Thus, analysing the importance of dispersal to periphytic populations allows us to discriminate between the two niche-based paradigms. From this perspective, our second hypothesis is that the distribution of periphytic assemblages is also dependent on both the waterbody morphometry and the meadow location. Distribution in the meadows from shallower macrophyte-dominated waterbodies follows the mass-effect paradigm assumptions. When assemblages are in isolated meadows in deeper aquatic ecosystems, their distribution corresponds better with the species-sorting paradigm. To test these two hypotheses, we analysed periphyton assemblages growing in several charophyte meadows in stagnant Spanish waterbodies. The selected meadows differ in terms of charophyte species and the environmental conditions of their locations. Our results confirm our first hypothesis: Characeans exert an influence on periphyton composition and diversity. Thus, a niche-based process occurs in which meadows are patches, and the main mechanisms operating, linked to the phylogeny of characeans, are allelopathy, competition and host substrate-attachment processes, all of which are still poorly known in characeans. Furthermore, the host-periphyton relationship with seston seems to be dependent on both the waterbody morphometry and the meadow location. Therefore, our second hypothesis was also supported; while shallower sites shared more periphytic and planktonic species, suggesting contributions of mass-effect and patch dispersion processes, the more isolated meadows shared very few periphyton species with water column assemblages, thus supporting the species-sorting paradigm. Therefore, periphytic assemblages growing on charophytes promote the diversity of pelagial habitats and might enhance both channels (benthic and planktic) of carbon uptake and flux throughout the food web. However, and despite their demonstrated importance in all freshwater environments, our knowledge regarding the structure and dynamics of the charophyte-periphyton relationship is still poor, and we make a plea here to increase it.
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Document Type: Research Article
Publication date: June 1, 2017
This article was made available online on June 9, 2017 as a Fast Track article with title: "Microalgal and cyanobacterial assemblages on charophytes: a metacommunity perspective".
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