Mapping and assessing marine ecosystem services supply in the Baltic Sea.

Coastal and marine ecosystems supply multiple Ecosystem Services (ES). Nevertheless, these ecosystems are among the most impacted by human activities, harming the ES sustainable supply. Since ES are a spatial phenomenon, mapping can contribute to understand ES supply. For this, we use quantitative spatio-temporal frameworks to map and assess the supply of one provisioning (food from fisheries) and two regulating ES (nursery habitats and nutrient regulation), considering two periods: Baltic Sea Holistic Assessment (HOLAS) 2 (2011-2016) and 3 (2016-2021). The ES supply was assessed following a process-based modelling approach, using bio-physical indicators as proxies. The three ES models were applied and validated, showing moderate results. For fisheries and nursery ES the results showed a significantly higher supply in HOLAS 3 than in 2, and for nutrient ES the opposite. This indicates that the assessed ES changed due to environmental activities. The Anselin Local Moran's results showed that most ES index values aggregate in the High-High cluster; Moran's I and semi-variogram results showed a clustered pattern; and the Getis Ord* analysis showed that hot and cold spots corresponded to high and low supply areas. For fisheries, high ES supply areas were located in the central-southern part of the Baltic Sea, while low-supply regions were located in the northern part. For nursery ES, high supply areas were located in the southwestern Finnish and western Estonian coasts. For nutrient ES, high supply areas occurred in the central- and eastern-southern parts close to the coast. Correlations showed a statistically significant negative correlation between fisheries and nursery ES and a significant positive correlation between fisheries and nutrient ES. No statistically significant correlations were observed between nursery and nutrient ES supply. The results obtained are essential to support coastal and marine management and planning in the Baltic Sea as well as international environmental policies and directives.