Is there going to be a meagre future for animals living on the seafloor of the Baltic Sea?

In the future, climate change and diminishing nutrient loads may reduce the amount of animals living on the seafloor in the Baltic Sea. This benthic fauna has so far been increasing in shallow waters during past eutrophication, and this has more than compensated for the hypoxia-driven loss of fauna in deeper bottom areas.

The doctoral thesis of Eva Ehrnsten from the Faculty of Biological and Environmental Sciences combines a mechanistic model of biomass production in the Baltic Sea with analyses of long-term monitoring data of benthic fauna.

Without understanding the production of benthic fauna it is difficult to understand links between eutrophication, climate change and the biodiversity of seafloor communities, and to make quantitative estimates of the role of benthic fauna for carbon cycling.

Computer simulations show that the total amount of benthic fauna has increased by about 50 per cent since the 1970s. Benthic fauna aid in the degradation of algae and other organic matter sinking to the bottom, bringing it back into circulation to be used by the food-web of algae, zooplankton and fish. The seafloor animals are also themselves a food source for many fish species.

Today, benthic fauna degrade about a fifth of the organic matter sinking to the bottom. In the future, the situation might be very different. The reduced nutrient loads may decrease the production of algae. At the same time, climate change is expected to increase water temperatures in the Baltic Sea.

"According to the modelling results, this will lead to more intense recycling of sinking organic matter in the water column, and in less food for benthic fauna. Not only is the amount of benthic fauna projected to decrease, but also their role in carbon cycling," says Eva Ehrnsten, who conducted her research in the Baltic Bridge collaboration between Tvärminne Zoological Station, Hanko, Finland, and Stockholm University Baltic Sea Centre.


Eva Ehrnsten's doctoral dissertation: Quantifying biomass and carbon processing of benthic fauna in a coastal sea – past, present and future