Temporal and spatial changes in benthic invertebrate trophic networks along a salinity gradient

Species interactions underlie all ecosystem goods and services and are important for understanding ecosystem changes. Representing one type of species interaction, trophic networks are able to be constructed from biodiversity monitoring data and known trophic links to understand how ecosystems have changed over time. The Baltic Sea is subject to high anthropogenic pressures, and its low species diversity makes it an ideal candidate for understanding how pressures change food webs. In this study, we used benthic monitoring data from 20 years (1980-1989 and 2010-2019) from the Swedish coast of the Baltic Sea and Skagerrak to investigate changes in benthic invertebrate trophic interactions. We constructed food webs and calculated traditional food web metrics that we compared over space and time. Our results show that the west coast of Sweden (Skagerrak) showed a reduction in benthic invertebrate biodiversity by 40% between the 1980's and 2010's, and that the number of links, linkage diversity, generality of predators, and vulnerability of prey have been significantly reduced. However, connectance has not significantly changed in the Skagerrak. The other basins (Bothnian Sea, Baltic Proper and Bornholm Basin) do not show any consistent significant trends in any food web metrics investigated, demonstrating resilience at a lower species diversity. The decreased complexity of the Skagerrak food webs indicates vulnerability to further perturbations and pressures should be limited as much as possible to ensure continued ecosystem functions.