LAUSR

Information on the spatial patterns and habitat preferences of marine species is key to understand the functioning of marine ecosystem and to manage and protect marine resources efficiently. However, the study of spatial patterns of marine ecosystems is challenging because they are dynamic environments that can vary seasonally. We analysed the spatial patterns of abundance, biomass, and biodiversity (richness and Shannon indices) of a northwestern Mediterranean demersal community and changes in these patterns between two different seasons. We modelled observed spatial patterns by season using hierarchical Bayesian spatial models and environmental, physical and anthropogenic factors. We identified the main drivers of fish, cephalopods, crustaceans and demersal assemblage spatial and seasonal patterns. Overall, our findings revealed the importance of seasonality in the spatial patterns of the demersal community, which were mainly driven by sea surface temperature. Results also underlined important patterns of movements of demersal organisms: fishes showed a general move from the upper-slope in winter to the continental shelf in summer, cephalopods showed a move from the northern part of the study area in winter to the southern part in summer, and crustaceans showed high densities in the area surrounding the Ebro Delta River in winter mainly driven by species-specific behaviour. Our results are relevant to inform future management measures 1 in the study area, such as seasonal fishing restrictions to protect specific aggregations of organisms during reproduction or feeding, or to adapt local marine protected areas to seasonal processes. This study provides evidence of the need to expand current monitoring schemes to capture the seasonality of marine demersal communities for a more comprehensive marine spatial planning framework.