Browsing by Author "Saari, Petra"

Eutrophication and climate change are considered to be the worst threats to the Baltic Sea ecosystem. The goal of this work is to understand, what are the consequences of environmental change to the distribution of Fucus spp., one of the key species of the Baltic Sea. Of particular interest here is to find the role of light and water turbidity in defining Fucus spp. distribution since scenario models of the effect of water turbidity defining the distribution has yet remained less studied. Nemo-SCOBI model of physical and biogeochemical conditions of the Baltic Sea calibrated according to different eutrophication and climate change scenarios were used in species distribution modelling (SDM) to predict future distribution of Fucus spp. The SDM method that was used was a regression-tree-based machine-learning generalized boosting method (GBM). In the modelling over 30 000 species presence and absence observations and six environmental variables (temperature, salinity, light attenuation, depth attenuated wave exposition and two seafloor types) were used. Water turbidity decreased in all scenarios in the areas where Fucus spp. occur but the BSAP was more beneficial scenario than the worst case scenario. Salinity decreased more and temperature increased less in the RCP8.5 scenario than in the RCP4.5 scenario. On top of that temperature decreased in the west coast of Finland in the RCP8.5 scenario. Suitable area for Fucus spp. declined in all scenarios so that the average occurrence probability decreased 11–30 percentage points. If no climate and eutrophication objectives (the Baltic Sea Action Plan and the RCP4.5) were met the average occurrence probability declined 25 percentage points. The situation for Fucus spp. is quite alarming because even if all the objectives would be achieved the suitable environment will nevertheless decline. If no actions will be taken in order to reduce nutrients the average occurrence probability declines 11–25 percentage points. Temperature decline in the RCP8.5 scenarios is thought to be caused by increasing upwelling events in the future, which may increase nutrient amounts in the coastal waters. The weak response to light and temperature and strong response to salinity and the fact that salinity decreased in all scenarios may explain why suitable areas decreased in all scenarios. There were some inconsistencies between the results and literature since the most optimistic scenario was the RCP4.5 & worst case, where BSAP goals are not achieved. This can be due to lack of species observations in the whole environmental gradients. The prediction results in the areas where water will be clearer in the future are not reliable and presumably more positive than these results show. While the BSAP scenarios may be too pessimistic the results of worst case scenarios are more reliable.