NEWS
More rain, larger inflow of river water and potentially less fish production. That is the projected future in the Baltic Sea, according to the thesis of Rickard Degerman at Umeå University.
Rickard Degerman. Photo UMF
Microscopic bacteria and phytoplankton constitute the base of the food web. At every trophic level, a significant part of the consumed energy is lost. Consequently a smaller fraction of the basal production within the system will reach the highest trophic level in food webs dominated by heterotrophic bacterial production compared to food webs based on phytoplankton production.
Rickard Degerman has performed his PhD studies within the EcoChange programme, and the main focus of his work has been the increasing inflow of organic matter to the northern parts of the Baltic Sea. According to the thesis, the amount of steps in the food web will increase, which leads to a decreased production at the top levels. But the ecosystem is complex, and there are many factors that might counteract the effects.
Current climate change scenarios show that precipitation will increase along with temperature in northern Europe. This will lead to higher river discharge to the Baltic Sea, which will be accompanied by higher inflow of organic matter from the terrestrial system. In Rickard Degerman’s thesis he shows that the increased inflow of organic matter will increase the bacterial production and alter the ratio between bacterial production and phytoplankton production.
Illustration by Mats Minnhagen.
This will probably have a negative effect on higher levels of the food web. However, the marine ecosystem is complex, and the effects may be counteracted by other factors. For example, fish has a relatively high temperature optimum, and therefore the loss of energy due to the increased number of steps in the food web might be compensated by a higher fish production caused by the higher temperature.
Rickard Degerman has performed both small scale laboratory studies and large scale mesocosm studies, using water samples from monitoring stations in the northern Baltic Sea. He also has performed a theoretical study, where he was able to test the effect of different climate change scenarios by using a mechanistic ecosystem model.
In summary, the thesis indicates that climate change probably will alter the food web structure and function in the coastal areas of northern Europe, as a result of increased inflow of organic matter together with a higher temperature. The complex effects on the ecosystem in the Baltic Sea, which has low species diversity and is highly vulnerable to environmental change, are of great importance to consider in the management of the future Baltic Sea.
