Almost Seven Decades of Coastal Bird Community Recovery Across Three European Seas.

Marine ecosystems have been historically impacted by human activities, leading to significant declines in biodiversity. Despite conservation efforts and the establishment of protected areas over recent decades, many marine species remain threatened. Here, we used a large-scale database of 308 time series of coastal bird communities collected between 1957 and 2024 across three European regional seas to assess how abundance, taxonomic and functional diversity have changed over the past decades, and to evaluate the effect of conservation areas on coastal bird communities. Our results showed overall increases in taxonomic richness (1.7% per year on average), taxonomic diversity (1.4%), abundance (2.7%), functional richness (4.1%) and functional evenness (0.7%) of coastal bird communities. Although these overall increases were similar across the three seas investigated, they were not uniform within them. Recovery in the Western Mediterranean Sea occurred primarily between 1970 and 2000, while in the Baltic Sea, increases have occurred since 1995. For the Baltic Sea, we also found that taxonomic and functional richness, along with total abundance, are increasing more rapidly in wintering compared to breeding communities. Besides the overall mean increases, trends were highly variable across sites, including 4.5% of them experiencing significant declines in species richness, 5.2% in taxonomic diversity, and 13.3% in abundance. This site-scale variability underscores the need for targeted conservation strategies that address local challenges. Our results also showed the relevance of conservation areas for coastal birds, especially those strictly protected. However, the effectiveness of protection depends on additional factors beyond the formal protection status alone. As some anthropogenic pressures persist, additional conservation actions are needed to ensure that marine bird communities continue to recover, but also to maintain stability in those populations that may have reached their carrying capacity.