Effects of projected climate change induced changes in wind patterns on the spatial distribution of blue mussels

Abstract

The projected changing climate is expected to have impacts on sea temperatures and salinities. In addition, wind patterns are projected to shift. Although projections are uncertain, noticeable changes in wind directions and patterns have already been recorded in the Baltic Sea, due to changing climate during the past decades. Wave exposure is one of the most important environmental factor controlling blue mussel (Mytilus trossulus) distribution and densities. Higher exposure keeps e.g. sedimentation at a lower level, which is beneficial for the species. Sea surface wave exposure is determined by wind power and direction, additionally by below surface topography. In the northern Baltic Sea, south-western winds prevail. It is assumed that blue mussels occur at higher densities on the exposed western and south-western sides of islands, islets and reefs. The blue mussel is a key species providing several ecosystem services, such as removal of organic nutrients by filtering water and being the main food source for many Baltic flagship species. So it is of great ecological interest to try to predict how, and where, this species will manage in the changing environment. The blue mussel data used in this study has been collected by diving, mainly within the Finnish Inventory Program for the Underwater Marine Environment (VELMU) and samples collected 2011-2015 were included. For this study, we started by running a distribution model for blue mussel densities, using wave exposure models produced with current wind data, in combination with other relevant environmental predictors. We ran models using exposure, produced with changed wind patterns, some of which follow predictions, while some are more extreme. The aim was to see how the pattern of occurrence changes in the fragmented archipelago of southern Finland and to see if there are significant shifts in occurrences within current protected area boundaries and if currently implemented MPAs Results show decreasing mussel densities with shifts towards northerly winds. Also changes in locations occurred, but these shifts might not be relevant for the planning of large MPAs, if the areas include a wide range of possible exposures. On the other hand, decreasing densities might affect the way the species provides its ecosystem services.