Out of the shadow and into the light: The functional diversity of the Baltic Sea

Background/Question/Methods

The Baltic Sea, a large brackish water area, is characterized by a persistent vertical and horizontal salinity gradient. Along this gradient ten distinguishable regions can be identified, the Kattegat, Belts and Sound, Arkona, Southwest, Eastern and Northwest of the Baltic Proper, Gulf of Riga, Gulf of Finland, Bothnian Sea and Bay. Due to its harsh physical conditions (ranges of low temperatures opposite to high temperatures and varying salinity values ranging from 1 to 25 psu, the Baltic Sea was assumed to be a low diversity system compared to other marine systems. There is increasing evidence that disturbances on ecosystems, via changes in species richness, species composition and community structure will affect important ecosystem functions and service provision. Characterising the relationship between ecosystem functioning and biodiversity is a challenging task, it is accepted that functional diversity of organisms sustains ecosystem. This raises the fundamental issue on how best to classify a functional species and how to assign functional traits. We used a new trait classification system (Jacob et al. 2011), to identify for the first time how the environmental gradients affect the functional structure of the Baltic Sea communities. The selected traits are considered important for ecosystem functioning and service provision.

Results/Conclusions

Categorising different types of predation, habitat use and functional characteristics is one way to classify the extent to which species interact with each other. Here we classify consumers by feeding mode, and the general nature of the interaction (i.e. herbivorous, carnivorous or omnivorous) between predator and prey species. More specifically, we consider the feeding strategy, habitat, and mobility of the consumer and trophic type/position of the prey as important characteristics of the consumer species, as well as its taxonomy and physiology. Applying these classifications to 6065 species, we derived different functional groups in terms of their trophic ecology, taxonomy, and functional ecology. We suggest that these are useful additions to traditional descriptions of community structure that will aid in linking food web structure to ecosystem functioning. Assuming that the emergent behavior of an ecosystem is dependent on the properties of the species it is composed of, we have looked into different properties and how they are distributed within the overall ecosystem structure which paves the road towards understanding the role of the functional and life-history traits of species, and the many services provided by ecosystems, the relationship between functional traits and to species taxonomy, ecological network structure and functioning.