What are potential future states of the Baltic Sea food web?

Barbara Bauer1, Bo Gustafsson1, Kari Hyytiäinen2, H. E. Markus Meier3,4, Bärbel Müller-Karulis1, Sofia Saraiva4,5 and Maciej T. Tomczak1

 

1 Stockholm University Baltic Sea Centre, Stockholm, Sweden

2 Department of Economics and Management, University of Helsinki, Finland

3 Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany

4 Swedish Meteorological and Hydrological Institute, Norrköping, Sweden

5 University of Lisbon, Instituto Superior Técnico, Environment and Energy Section, Lisbon, Portugal

 

The Baltic Sea ecosystem is subject to multiple interacting human pressures, with substantial impacts on the state of the marine ecosystem. Our goal here was to investigate the relative importance of selected pressures under various pathways of changing climate and society around the Baltic Sea and identify the ones with the largest impact on the marine ecosystem. To achieve this goal, we compiled quantitative simulations of plausible future states of the marine ecosystem under five scenarios. The scenarios are based on consistent storylines for plausible developments of climatic factors and socio-economic drivers in the Baltic Sea region.

Socio-economic drivers were translated as pressures concerning evolution of the type of fisheries and nutrient pollution. The latter, together with regionally downscaled global trends in climate were the basis of computing abiotic habitat quality for benthic and demersal marine fauna both at lower and higher trophic levels. We achieved this by using outputs from a coupled physical-biogeochemical model as forcing in a spatially resolved ecosystem model of the offshore Baltic Sea, together with fisheries forcing, which we defined based on scenario narratives. The ecosystem model provided spatially explicit projections of the development of marine fauna, including benthos, fish populations, seals, offshore feeding birds and commercial fish catches. We analyzed each scenario in terms of pressures on the ecosystem and the ecosystem’s response to those, especially concerning state of habitats, fish populations and biodiversity. The scenario assuming a sustainable society (low greenhouse gas emissions, the implementation of the Baltic Sea action Plan and fisheries aimed at maintaining ecosystem integrity) resulted in an increased capacity of the Baltic Sea to maintain diverse communities. In contrast, the scenario envisioning increasing inequality, high greenhouse gas emissions and continuing nutrient pollution due to weak environmental regulations resulted in decreased habitat quality, very high fishing pressure and diminished biodiversity. We hope that our exploratory study provides inspiration and a broader context for strategic level discussions with stakeholders about the future of the Baltic Sea food web and society.