Essential young-of-the-year fish macrophyte habitats along the swedish east coast

Along the coastal zone of the Baltic Sea high productivity habitats form important areas for many organisms, including young-of-the-year (YOY) fish. Habitats consisting of aquatic vegetation provide YOY fish with important services, such as refuge from large predators and food sources. However, relationships between YOY fish abundance/species richness and habitat cover, and environmental variables across multiple scales, remains unclear, as well as the relationship between essential YOY fish habitats and different intensities of recreational boating. Additionally, the amount of essential YOY fish habitats protected by marine protected areas (MPAs) is unknown. To address these questions relationships between YOY fish and habitat/environmental variables were analyzed for a large data set consisting of 4,670 samples along the Swedish Baltic Sea coast using Generalized Additive Models (GAMs). Samples were collected by SLU Aqua between 2007 and 2018 using small underwater detonations and estimation of habitat cover was conducted by snorkeling. Spatial analyses using ArcGIS Pro 2.5.0 were conducted to study the correlation between boating activity and the density of essential YOY fish habitats, and the representativity of YOY fish habitats within the MPA network. Overall, there was a significant relationship between vegetated coastal habitats and YOY fish abundance and species richness, by displaying a higher abundance and species richness of YOY fish in areas with a higher vegetation cover. Significant relationships between individual YOY fish species and different types of vegetation were also found. However, based on the spatial analyses these valuable YOY fish habitats were insufficiently covered by the MPA network, with only 13 % overall cover. A target of 30 % protection is suggested by the European Commission and is a central part of the EU Biodiversity Strategy for 2030. Furthermore, the valuable habitats are highly subjected to boating activity posing a risk for a decrease in the distribution of YOY fish habitats. Therefore, it is strongly encouraged to consider location refinement, expansion, and updated management of the MPA network, and to regulate the average number of boats allowed in ecologically valuable areas