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Climate change threatens marine environment in the northern Baltic Sea  

​Photo: Lotta Nygård

​The unique Baltic Sea is one of the focal points of climate change. One could think the contrary, but the effects of climate change will be significant.

There are many modelling tools and scenarios used for constructing climate projections for the future Baltic Sea, but the actual effects of climate change on marine nature and on people are not clear. Marine spatial planning contributes to the sustainable growth and development of different uses and the good status of marine waters. However, this is difficult to achieve without a tangible vision of what the future looks like: and this is something that is currently missing at local and regional level. Climate change is one of the humanity's greatest challenges and all European countries are challenged to consider their own actions and environmental responsibility.

The brackish Baltic Sea is a young marine region, which has not yet its own established species assemblage. Both marine and freshwater species experience difficulties, when faced with the brackish water environment: the salinity is either too high or too low. Living in harsh conditions can be stressful and energy consuming, which is why the adult size of many species in the Baltic Sea is much smaller than elsewhere. The environmental conditions in the Baltic Sea change regionally, like in the Gulf of Bothnia (northernmost part of the Baltic Sea), where the salinity variation is the steepest. Salinity decreases drastically in the central Gulf of Bothnia, which is the northernmost distribution boundary for marine species. In addition, winters and sea ice present an extra challenge for species' adaptation. Because of its special features, the Gulf of Bothnia is particularly sensitive area for the effects of climate change, and in hundred years the underwater nature of the area may look completely different.

Climate change will increase precipitation, which leads to decreased salinity level in the Baltic Sea. Already low-saline and brackish water challenges species, and the decrease in salinity caused by climate change will change geographical distributions of species. The Gulf of Bothnia is inhabited by important keystone species, such as blue mussel (Mytilus trossulus) and bladder wrack (Fucus vesiculosus), whose distributions are limited by salinity: as marine species, they already live on the verge of their existence due to almost fresh water environment in the Gulf of Bothnia. Keystone species produce essential and free ecosystem services, which effect on our everyday life. Blue mussels, for example, recycle nutrients and clear water, whereas bladder wrack functions as an important habitat for invertebrates and juvenile fish. Keystone species are species, which affect directly or indirectly on another species. If keystone species disappear, it can have a larger scale negative impact on the biodiversity of the Baltic Sea. Losing species means losing natural capital, which sets a direct threat towards people's well-being.

The Gulf of Bothnia is also one of the shallowest areas in the Baltic Sea, and due to small water volume and northern location, the area is prone to warming. Already icy winters have become shorter. Due to the combined effects of low salinity and higher temperature, many species are likely to disappear from the northern Baltic Sea.

An Interreg Botnia-Atlantica project ECOnnect was launched in 2018, and it studies the impact of climate change on underwater marine nature in the Gulf of Bothnia. ECOnnect is a cross-border cooperation project between Finland and Sweden and it produces the first comprehensive assessment of the future Baltic Sea marine nature regardless of administrative boundaries.

The EU-programme Interreg Botnia-Atlantica is the main funder of project ECOnnect. Other funders are Swedish Agency for Marine and Water Management and Regional Council of Ostrobothnia. The project partners are County Administrative Board of Västerbotten and Västernorrland, Metsähallitus Parks & Wildlife and Centre for Economic Development, Transport and the Environment of South Ostrobothnia.