Biodiversity trends for five European marine biotic groups

Biodiversity loss is one of the main global-scale challenges our planet is facing. In European marine and coastal waters, biodiversity loss is caused by multiple human activities such as overfishing (reducing fish and invertebrate stocks and harming vulnerable species) and climate change (shifting species distribution towards colder waters and enabling biological invasions of species from warmer waters). As the causes of biodiversity loss in European marine ecosystems were identified, legislation and policies to counteract the losses were implemented. For example, the Common Fisheries Policy introduces fishing quotas and Marine Protected Areas limit some of the most prejudicial human activities. In sum, there are two opposing processes acting on coastal and marine biodiversity: losses caused by human activities and gains caused by conservation efforts.

We aim to describe European marine and coastal biodiversity temporal trends to understand if biodiversity loss is worsening, stagnant or improving. We also want to determine if these trends are similar across European regions and for different groups of organisms. To do so, we estimated the temporal trends in richness, diversity and abundance for five biotic groups (i.e. fish, invertebrates, macroalgae, phytoplankton and zooplankton) across five European regions (i.e. Atlantic Ocean, Arctic Ocean, Baltic Sea, Black Sea and Mediterranean Sea).

The data was extracted from open-access databases (BioTIME, EMODnet, REPHY, FishGlob, Continuous Plankton Recorder Survey), the final dataset comprising 2,066 time series, spanning from 1956 to 2022 with a mean total duration of 18 years and a mean of 15 sampled years. For each time series and metric, we fitted a Generalized Least Squares (GLS) model and, to detect differences in the trends across geographical regions, the resulting slopes of the GLS models were meta-analysed.

Most communities showed no significant change, suggesting no further widespread biodiversity loss during the observation period. Positive trends were found for invertebrates in the Baltic, and negative ones for fish in the Atlantic. However, uneven data coverage limits this generalization, highlighting the lack of sufficient rigorous monitoring of biodiversity and of accessibility to existing data.