Global environmental change has recently accelerated at unprecedented rates leading to a rise in novelty of environments and ecological communities. Previous studies have shown that novelty of terrestrial ecosystems changes over time and space, and related the rise of novelty to climate and land-use changes. However, such studies typically focused either only on environmental novelty (typically climate novelty), or on the relationships between environmental novelty and ecological novelty of single ecological communities. To further advance this field, we analyze for the first time both environmental and ecological novelty in a large marine system (the Baltic Sea) for three trophic groups (phytoplankton, zooplankton, and fish), and explore potential causes of novelty emergence that may be relevant for marine conservation and management. We measure novelty as the degree of dissimilarity of the marine system compared to a specific reference baseline for four ecosystem components: environmental variables (salinity, temperature, nutrient concentrations), phytoplankton, zooplankton, and fish communities, using 36-years long monitoring data series (1979- 2015) of the Baltic Sea.
Results/Conclusions
Environmental novelty in the Baltic Sea was particularly high for surface and bottom salinity and temperature, in particular in early 1990s. Spatially, some basins show a high environmental novelty, like the Northern basins, whereby the temporal novelty variability is very high in the Central Baltic Sea basins. The magnitude and temporal dynamics of ecological novelty in the three trophic groups is complex and dependent on multiple abiotic factors and ecological interactions. In addition, we found different temporal dynamics between abundance and species turnover within each of the trophic groups. Environmental variables, in particular salinity, temperature and nutrients, partly explain these temporal and spatial dynamics of ecological novelty, but the effects are basin specific and vary across biotic groups. There appears to be a great potential in analyzing novelty on a whole-ecosystem perspective as it improves the understanding of the response of ecological communities to multiple drivers. We suggest that understanding the emergence of environmental and ecological novelty in relation to the restoration potential of certain species and their habitat is needed for setting management baselines and targets.