Årsta havsbad. Photo Carina Andreasson /Mostphotos

With computer models, it is possible to create well-founded visions of what the marine environment may look like in the future. The range of ecosystem services, such as a relaxing swim in the ocean, fresh fish or oxygen producing algae, is affected by the balance of the marine ecosystem.

In the Baltic Sea case, many factors have implications on ecosystem services, such as environmental change and societal development both on land and in water. By using projections, a study from the BalticAPP research project has for the first time examined how the Baltic Sea's ecosystem services can change in the future.

– We have, for instance, taken the IPCC's global climate projections and applied various projections of what our society might look like in a hundred years. This is a first example of how new interdisciplinary models help us study complex relationships between society and the environment and also project them into the future to see how ecosystem services can change, says Eva Ehrnsten, researcher in ecosystem dynamics at the Baltic Sea Center and co-author of the study.

The study highlights a pessimistic and optimistic path for the Baltic Sea. The first scenario examines a fossil-fueled developmentwhere the global climate effects become significant (which corresponds to the IPCC's climate scenario RCP 8.5). Fisheries are driven by profit maximization and no new measures are taken to prevent eutrophication of the sea. Factors such as population growth and how dietary habits affect agriculture in the Baltic Sea region have also been included.

– There are global projections that we have scaled down to a Baltic Sea level. For example, how many farms or cows around the Baltic Sea do the different food production scenarios involve? From there, we have linked hydrodynamic, biogeochemical and ecological models that show what emissions these sources lead to, what it means for the ecosystem and ultimately for the ecosystem services that we have chosen to investigate, says Eva Ehrnsten.

Expanding hypoxia and fewer summer swims

The models show that a warmer sea, with continued high nutrient loads and fishing pressure result in clear changes of the ecosystem. In almost the entire Baltic Sea, increased cyanobacterial blooms are expected during the summer.

– Days with algae blooms are something that hinders our access to recreation. For instance, you don’t want to go out swimming or boating during blooms. Today we have an average of 60 algae blooming days per summer season, but in some cases, it can increase to 80 days between May and October, under these conditions, says Eva Ehrnsten.

Algae blooms and increased primary production affect how the oxygen-free sea floor expands or retracts and what species benefit when the water becomes more turbid.

– Eutrophication feeds the system which makes more biomass available. In this scenario, we can see that it actually benefits a lot of "trash fish" that are less commercially profitable.

Eva Ehrnsten, forskare inom ekosystemdynamik vid Stockholms universitets Östersjöcentrum.

Less algal blooming and more diverse fish communities

The second, sustainable well-being scenario, assumes that global development occurs in accordance with the UN's global sustainability goals and a strong climate policy that will cause emissions to culminate by 2040. In this scenario, the nutrient supply to the sea is in compliance with the Baltic Sea Action Plan and fisheries are conducted with great consideration to the ecosystem.

Under such conditions, models show that the Baltic sea floor is recovering from hypoxic conditions and that benthic species are established in new areas, both in the sediment and in the water.

– In the sustainable well-being alternative, we can see that more food is available for demersal fish, such as flounders, which are economically valuable species. In our models, we see an increase in these in future catches, says Eva Ehrnsten.

And in addition to a greater diversity in the fish community and catches, a clear development of the algal blooms can also be detected here.

– In all basins, or parts of the Baltic Sea, you see that the number of algae bloom days decreases, compared to today. In some cases, such as in the Bornholm Basin, the blooming period was reduced by half, from 60 to 30 days.

The truth is somewhere in between

The study demonstrates new possibilities with these combined research areas and shows overall images of the future with clearly differing developments in primary production as well as fish catches and recreational opportunities. Eva Ehrnsten emphasizes, however, that they indicate a range of possibilities rather than a definite conclusion.

– Scenarios are by definition guesses and used when you do not know what the future looks like. We use the best case scenario and the worst case scenario to see what can happen, but the realistic future is probably somewhere in between, she concludes.

Text: Isabell Stenson