Future of the Gulf of Bothnia

Before we jump into the future of the Gulf of Bothnia, it is time to let the Baltic Sea tell her story in a video.

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All the species in the world are adapted to certain environmental conditions through the slow process of evolution. If the environment changes suddenly, species must adapt to the new conditions or move to areas with better conditions. The climate is changing faster than species have time to adapt, and in the worst case, species may decline or disappear locally.

Over the next 100 years, the mean water temperature will increase, and the ice thickness will be reduced considerably within the central Gulf of Bothnia. This is shown in the project ECOnnect's research that are based on the Swedish Meteorological and Hydrological Institute SMHI’s and the Meteorological Institute in Finland FMI's future scenario models. The mentioned changes can have a negative effect on some species. Reducing ice thickness affects directly for example the Baltic ringed seals as they give birth in snow caves on the ice. Warming water temperature will have a negative effect on cold water fish species such as whitefish as they are adapted to live and reproduce in colder waters. There might also be some species, such as warm water fish species like cyprinids, that can benefit from the warming waters.

On the other hand, ecosystems are complex, and species are not only affected by climate change but also by other human stressors such as habitat destruction, pollution, eutrophication, and overfishing. Species are also affected by other species. For example, warming water can speed up the development of warm water fish larvae, but their prey species might suffer because of the rising temperature. It is hard to know for sure which species will be negatively affected by climate change and which species will be positively affected. 

Ecosystem services are natural conditions and processes that benefit humans. The Baltic Sea offers us direct services like fish catches. Indirect ecosystem services are often forgotten because they are harder to see. These include vital supporting services where for example living organisms neutralise toxins or bottom fauna and bacteria recycle nutrients. Various plants forming underwater meadows also help to provide ecosystem services since they generate food, habitats and hiding places for fish and baby fish. Additionally, ecosystems provide cultural services like swimming, boating, and ice skating in winter.

Climate change affects many species living in the Baltic Sea, and it can also affect the services the species produce. If species diversity deteriorates as predicted, it will not only affect the ecosystems’ ability to adapt to environmental changes but will also result in loss of ecosystem services. Additionally, more harmful alien species could spread to central Gulf of Bothnia with warming temperatures, which threatens native species through competition, predation, and transmission of pathogens.

The cultural services provided by the sea are not spared from the effects of climate change either. Activities like swimming and diving will be affected if harmful algal outbreaks become more common in summertime due to warming water. Winter activities such as sea ice skating and ice fishing could be lost because the ice cover is going to get thinner. Climate change can also deteriorate cultural heritage both on land and underwater through erosion, changes in the chemical composition of water, or increased flooding. Due to long history in seafaring and fishing in the area, there is a rich cultural heritage with multiple wrecks, fishing huts, and lighthouses.

All their time spent on the sea gives fishers front row seats in experiencing and noticing the changes in the underwater environment, from season to season and year to year. They can notice changes for example in their catches, in water quality and temperature, in surrounding animal populations such as birds or seals, or in the ice cover in winter. On the shores of Gulf of Bothnia, especially the decreasing ice cover has become familiar to both professional and sport fishers. For them, this change has shifted fishing seasons as spring and autumn are longer compared to the winter season. Experts are also talking about the same changes and point out that climate change is happening right now. That is why we need to focus on making its effects as small as possible.

Would it not be interesting to peek into the future? To a certain extent we can do that by creating models that help us understand what the future could look like according to a certain set of variables. With models, we can for example estimate thickness of ice cover or predict where we might find blue mussels in the future. However, models always have uncertainties as they are limited by the input data. It is also impossible to know for sure how future climate, environment, society, and other factors will develop.

Below you can find a few future models as pair of maps where you can compare the past and the possible future by moving the slider tool on top of the maps. The models created for the central Gulf of Bothnia are based on SMHI's work and are produced in the project ECOnnect and focus on HELCOM Baltic Sea Action Plan’s nutrient reduction target and on IPCC's climate scenario RCP8.5 which represents the worst-case RCP climate scenario. This means that the models are based on the assumption that nutrient input into the sea is reduced but greenhouse gas concentration in the atmosphere continues to grow. 

The global warming is not happening only on land. We are also expecting an increase in water temperature in the future. You can see from the pair of maps that the mean temperature in the water layer closest to the sea floor can increase around 3 degrees in the summer months. Such a major rise will affect the living organisms in the water, especially the species that favour colder water.

Salinity describes the concentration of salt in the water. If there will be more rainfall in the future, it is likely that river run-off will also increase with more freshwater going into the sea. This would lower the salinity of the sea water. On the other hand, higher temperatures increase evaporation which could lead to a decrease in river run-off. This would not cause a decline in salinity. If sea level will rise, more saline water could flow from the Atlantic into the Baltic Sea. This potential effect is however not included in the models used in this project. It is hard to predict the future salinity levels in the sea because we cannot be certain about the future changes in river run-off and the water balance. Thus it is important to keep in mind that the salinity predictions we present here are based on certain mean future predictions but hold a lot of uncertainty in them.

As you can see from the pair of maps, salinity in the water layer closest to the sea floor might decrease by 10%. This is not a very big decrease, but the salinity in the area is already low for some marine species like the blue mussel. If salinity would decline more than the models show, it would have a great effect on several marine species in the area.

Along warming climate and water temperature, the ice cover will become thinner. This can have both negative and positive effects on the area. Ice skaters and fisher and some mammals will experience the lessening ice cover negatively. Some vegetation like bladder wrack and narrow wrack could be positively affected as the ice would not scrape it away from the shallow hard bottoms every winter.

From the pair of maps, you can see that we predict a possible over 80 % decline in mean ice thickness in the area. In practice, this means that the ice cover could become thinner by an average of 26 centimetres in about 100 years.

Bladder wrack (Fucus vesiculosus) and narrow wrack (Fucus radicans) are marine species growing on rocks and stones on the sea bottom usually at a depth of 0,5-5 metres. They are key stone species in the Baltic Sea as they make up important habitat for fish and invertebrates on hard bottoms.

The models show that there could be more potentially suitable areas for bladder wrack and narrow wrack to grow in the future. This is mainly due to thinner or missing ice cover. Ice usually scrapes away algae growing in shallow areas every year, but the lack of ice could make these areas available also for perennial algae such as bladder wrack and narrow wrack. As they are marine species, they require a certain level of salinity to thrive. The models in this study predict a small decline in salinity but the decline is so modest that it will not have a significant impact on the distribution of the species. Changes in salinity also affect the bladder wrack and narrow wrack species differently, narrow wrack is more tolerable to lower salinity and can manage predicted future salinity better than bladder wrack. However, if the future would look different and salinity would decrease more, then the distribution of both species would most probably decline.

If the nutrient reduction targets of the Baltic Sea Action Plan would be achieved the water quality would be improved which increases the maximum depth to which light is available in the water. Light is essential for the growth of all vegetation and increased light availability in the water can make more areas suitable for bladder wrack and narrow wrack as well as for other species.

The future distribution models of bladder wrack and narrow wrack are to some extent an overestimation as there likely will be some years with colder winters and thicker ice cover which would scrape away the species from shallow stony shores. Moreover, the models do not take into account bottom substrate and there will therefore be areas that the models display as suitable which might not be suitable for the species if the bottom substrate is not right.

Blue mussel (Mytilus trossulus x edulis) is also a marine species and it lives deeper than bladder wrack and narrow wrack at 8-12 metres depth. Together with bladder wrack it is one of the most important key species in the Baltic Sea as it is both food and habitat for other species. Blue mussels are the most important food source for common eider (Somateria mollissima). They also filtrate the water from nutrients and harmful substances. Blue mussels do not occur north of Kvarken as the salinity is too low there. The models suggest that the distribution of blue mussel may be significantly reduced in the future. This is mainly due to the slight decline in salinity and rise in water temperature. The modeled effect of declining salinity is greater on the blue mussel than on bladder wrack and narrow wrack because narrow wrack tolerates lower salinity and both species were included in the model.

The benthic amphipod (Monoporeia affinis) lives in the deep and soft bottoms of the Baltic Sea and is very abundant in the Gulf of Bothnia where bottom oxygen conditions are good. The amphipod makes up the basis for softbottom food webs and is an important food source for several fish species.

In the future, it can be expected that the species will suffer from the increasing water temperature as it is a cold-water species. It can be interpreted from the models that the shallow areas of Kvarken might become too hot in the future and hence be less suitable for the species. But this does not mean that the species would disappear entirely from these areas just that the area might not be suitable for such high densities of the species which were used in the models.

In our seas, species are constantly on the move. The movements of sea-dwellers, their seeds and propagules between habitats create connections or so-called ecological connectivity. It is extremely important for the survival of species in a changing environment because species need to be able to move into new habitats if some areas become degraded or inhabitable due to climate change or other human activities.

Some highly mobile species such as fish are able to move throughout their whole life cycle. Others, such as blue mussels and bladder wrack are stationary as adults and can only move by e.g. free-living propagules or larvae. Different species have also different abilities to disperse in the sea. For example, the blue mussel’s larvae can disperse up to 50 kilometres, whereas the bladder wrack, and aquatic plants with seeds can typically disperse only a few meters. This is important to consider when for example designing marine protected areas (MPAs). Sizes and locations of MPAs can be arranged to suit the species that need protection, and to enable connectivity between MPAs.

Climate change will very likely impact the connectivity of our species, but the question is in what ways and how much. With the help of field data-based models, we can predict how connectivity may change along climate change and simulate how the future might look like. In doing so, we can identify areas that are and will be important for keeping our seas connected. 

A healthy sea and ecosystems in it are more resilient to climate change, and together we can make the Gulf of Bothnia healthier. Big changes can start with small everyday actions. Have you for example considered eating domestic fish like bream or roach? Their populations are currently not under threat. Or have you considered the necessity of dredging? Even small-scale dredging can harm the marine nature for a long time.

Because the brackish Baltic Sea is shallow and the water changes slowly, it is very vulnerable to human activities and climate change. Locally, it is important that we reduce the amount of nutrients and harmful substances going to the sea, control littering, turn down undersea noise and prevent alien species spreading into our waters. Globally, we need to mitigate climate change by reducing greenhouse gas emissions via renewable energy sources, by increasing carbon sinks, and by using natural resources sustainably. After all, the main thing is that we act for our nature and not against it, both on land and at sea. 

•  Project ECOnnect's website , where you can find the project's final reports.
•  ECOnnect's YouTube channel , where you can find all the videos produced in the project.
•  SeaGIS map service , where you can find GIS-layers of the future models produced in the project ECOnnect.

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