Effects of an invasive polychaete on benthic phosphorus cycling at sea basin scale: An ecosystem disservice
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Macrofaunal activities in sediments modify nutrient fluxes in different ways including the expression of species-specific functional traits and density-dependent population processes. The invasive polychaete genus Marenzelleria was first observed in the Baltic Sea in the 1980s. It has caused changes in benthic processes and affected the functioning of ecosystem services such as nutrient regulation. The large-scale effects of these changes are not known. We estimated the current Marenzelleria spp. wet weight biomass in the Baltic Sea to be 60–87 kton (95% confidence interval). We assessed the potential impact of Marenzelleria spp. on phosphorus cycling using a spatially explicit model, comparing estimates of expected sediment to water phosphorus fluxes from a biophysical model to ecologically relevant experimental measurements of benthic phosphorus flux. The estimated yearly net increases (95% CI) in phosphorous flux due to Marenzelleria spp. were 4.2–6.1 kton based on the biophysical model and 6.3–9.1 kton based on experimental data. The current biomass densities of Marenzelleria spp. in the Baltic Sea enhance the phosphorus fluxes from sediment to water on a sea basin scale. Although high densities of Marenzelleria spp. can increase phosphorus retention locally, such biomass densities are uncommon. Thus, the major effect of Marenzelleria seems to be a large-scale net decrease in the self-cleaning capacity of the Baltic Sea that counteracts human efforts to mitigate eutrophication in the region.
KeywordsBenthic–pelagic coupling Ecosystem services Eutrophication Invasive species Nutrient cycling
The authors would like to thank the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) and Swedish Environmental Protection Agency (Naturvårdsverket) for financial support (VALUES Project), and Stockholm Marina Forskningscentrum (Östersjöcentrum) for time and space at Askö Laboratory; Andrey Sikorski for taxonomic expertise; Mats Westerbom for help with the OIVA database; Joanna Norkko, Ragnar Elmgren, Anna-Stiina Heiskanen, Eva Roth, and Gunilla Ejdung for valuable comments on the study; Two anonymous reviewers and the editor, whose comments greatly improved the manuscript; HELCOM as well as laboratory and field staff contributing to the benthic monitoring of the Baltic Sea.
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