Biodiversity assessment for coastal fish communities in the Baltic Sea

Abstract: Biodiversity becomes of increasing concern in management of marine ecosystems. Measures of biodiversity are numerous and have been largely developed. Biodiversity can be partitioned in different components that indicate, for example, spatial and temporal changes in any communities. Coastal fish communities in the Swedish Baltic Sea have a key role in ecosystem functioning and provide many ecosystem services. Therefore, monitoring biodiversity is essential as fish communities are under anthropogenic and environmental threats. In this study, Swedish coastal fish biodiversity is assessed at different spatial and temporal levels using alpha, beta and gamma diversities. Furthermore, as size is an important trait in fish ecology and is closely related to functions, biodiversity measures have also been estimated using size-classes instead of species. While alpha and gamma diversities have higher diversity in size-class than in taxonomic classification, the opposite is observed in beta diversities. Overall, no clear spatial pattern following the north-south environmental gradient characterizing differences between areas is found, suggesting that other factors might influence biodiversity along the Swedish coast. However, beta diversities show diversity in species composition and regime dominance within area, especially in southern Sweden. Beta diversity at year level showed that coastal fish communities have been quite stable these last eleven years but with some changes. Such comparison between species- and size-based diversity provide additional information on biodiversity in the Baltic Sea and could help for management and future investigation.