LAUSR

Summary Indicators of ecosystem status are of increasing importance for management. Many studies infer associations between the environment and fish communities, but little is known about how fish community indicators are related to temporal variation in anthropogenic and hydroclimate drivers, and on what geographical scale, these indicators are representative. Here, we investigate the spatial synchrony of seven indicators of coastal fish community status among eleven reference sites 2002–2014 in the Baltic Sea. At three of these sites, we study the temporal covariation between indicators and anthropogenic and hydroclimate drivers over 25 years. The indicators (abundance of) – Perch, Large Piscivores and Non-perch Piscivores – showed spatial synchrony over the study scale (100–1000 km), whereas temporal dynamics of other indicators reflected changes at scales <100 km. At the studied reference sites, temporal changes of indicators were mainly associated with climate-related hydrological variables, but nutrient-related variables were important in the northern Baltic Sea. Landings showed no associations with any indicator. Four of the indicators showed evident temporal autocorrelation reflecting an influence of internal population/community processes. Synthesis and applications. Environmental status of coastal fish communities in the Baltic Sea should be assessed and managed at a local scale. The main drivers of fish community indicators of ecosystem status tend to differ between coastal areas, but among the reference sites assessed in this study, hydroclimatic variation and internal processes seem to be of greater importance for the temporal development of indicators than anthropogenic pressures. Therefore, when assessing the status of coastal fish communities and evaluating management measures in areas impacted by anthropogenic activities, it is important to account for variation in salinity, temperature and time lags.