Environmental Context Mediates Biodiversity–Ecosystem Functioning Relationships in Coastal Soft-sediment Habitats
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The ongoing loss of biodiversity and global environmental changes severely affect the structure of coastal ecosystems. Consequences, in terms of ecosystem functioning, are, however, difficult to predict because the context dependency of the biodiversity–ecosystem function relationships within these heterogeneous seascapes is poorly understood. To assess the effects of biological and environmental factors in mediating ecosystem functioning (nutrient cycling) in different natural habitats, intact sediment cores were collected at 18 sites on a grain size gradient from coarse sand to silt, with varying organic matter content and vegetation. To assess ecosystem functioning, solute fluxes (O2, NH4+, PO43−, Si) across the sediment–water interface were measured. The macrofaunal communities changed along the grain size gradient with higher abundance, biomass and number of species in coarser sediments and in habitats with more vegetation. Across the whole gradient, the macrofauna cumulatively accounted for 25% of the variability in the multivariate solute fluxes, whereas environmental variables cumulatively accounted for 20%. Only the biomass and abundance of a few of the most dominant macrofauna species, not the number of species, appeared to contribute significantly to the nutrient recycling processes. Closer analyses of different sediment types (grouped into coarse, medium and fine sediment) showed that the macrofauna was an important predictor in all sediment types, but had the largest impact in fine and medium sediments. The results imply that even if the ecosystem functioning is similar in different sediment types, the underpinning mechanisms are different, which makes it challenging to generalize patterns of functioning across the heterogeneous shallow coastal zones.
Keywordsbiodiversity–ecosystem functioning benthic macrofauna sediment grain size solute fluxes environmental gradient spatial heterogeneity coastal zone Baltic Sea
This study was funded by Walter and Andrée de Nottbeck Foundation (JG, GB) and the BONUS COCOA project, which was supported by BONUS (Art 185), funded jointly by the EU and the Academy of Finland (AN), and the University of Helsinki (3-year grant to JN). We sincerely thank Judi Hewitt for valuable advice on statistical analyses, Emmi Hänninen for video analyses, and Hanna Halonen and trainees at Tvärminne Zoological Station for valuable practical assistance.
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Conflict of interest
The authors declare that they have no conflict of interest.
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