Description: Seagrass is a foundation species within shallow water ecosystems because it provides habitat and food and thereby supports biodiversity. It has a function as atmospheric CO2 storage and improves the water quality by filtering nutrients (Greiner et al. 2013). Currently, seagrass meadows are facing multiple challenges such as ocean warming, reduced light caused by increasing nutrient input and more frequent disturbance events or direct anthropogenic impact (Unsworth et al. 2019). All these factors affect the performance of seagrass and thereby impair the ecosystem services seagrass meadows provide. This thesis represents a systematic review and meta-analysis of the physiological effects of temperature change on seagrass to provide a better understanding of the effect of rising temperatures on seagrass meadows worldwide. In this thesis, 766 papers were reviewed and a subsequent meta-analysis of 43 papers including 407 control-treatment temperature combinations matching the inclusion criteria were conducted. The log response ratio (lnR) was used for calculating the effect sizes, because it is more intuitive to interpret. Hedges’ g was further used to verify the results. It was tested for effects of the physiological parameters measured, the treatment type, the temperature direction, the experiment duration, the control temperature, latitude and longitude of the source population and the genus on relative seagrass performance (lnR). The key results of the meta-analysis showed that (I) plant physiological performance was reduced by an average of 39% by temperature change across all studies; (II) per 1°C experimental ocean warming a reduction in seagrass performance of 11% was observed; (III) the measured performance parameters (growth, biomass, photosynthesis and survival) showed differential susceptibility to warming, with survival being most affected and photosynthesis least affected; (IV) seagrass genera did not differ significantly in their response to experimental ocean warming but varied between locations. There was a strong geographic bias in this meta-analysis since most case studies were conducted in developed countries including Europe, the US and Australia. Thus, many species were underrepresented while also some climate conditions were not covered. Further, it was also not possible to make a statement about the recovery after experimental temperature stress had ceased, as there were too few studies focusing on recovery. Altogether, this thesis identified two profound knowledge gaps, which should be addressed by future studies. In conclusion, more frequent and intense heat waves are an increasing threat to seagrass meadows in the future. As seagrass provides important ecological services, it needs to be protected. It is particularly striking that every degree Celsius of temperature change matters for seagrass as it means a reduction in physiological and morphological performance, which is another indication that global warming should be kept below 2 degrees Celsius

Description: Highlights: • We summarized 20 ecosystem services provided by coastal Baltic ecosystems. • Information on how services translate into socio-economic benefits is lacking. • The deep knowledge gap impairs the sustainable management of the benefits. • We propose a framework with four key measures to close this knowledge gap. • Toxins and Nutrients are the most well-document pressures to these services. Abstract: Seagrass meadows, algal forests and mussel beds are widely regarded as foundation species that support communities providing valuable ecosystem services in many coastal regions; however, quantitative evidence of the relationship is scarce. Using the Baltic Sea as a case study, a region of significant socio-economic importance in the northern hemisphere, we systematically synthesized the primary literature and summarized the current knowledge on ecosystem services derived from seagrass, macroalgae, and mussels (see animated video summary of the manuscript: Video abstract). We found 1740 individual ecosystem service records (ESR), 61% of which were related to macroalgae, 26% to mussel beds and 13% to seagrass meadows. The most frequently reported ecosystem services were raw material (533 ESR), habitat provision (262 ESR) and regulation of pollutants (215 ESR). Toxins (356 ESR) and nutrients (302 ESR) were the most well-documented pressures to services provided by coastal ecosystems. Next, we assessed the current state of knowledge as well as knowledge transfer of ecosystem services to policies through natural, social, human and economic dimensions, using a systematic scoring tool, the Eco-GAME matrix. We found good quantitative information about how ecosystems generated the service but almost no knowledge of how they translate into socio-economic benefits (8 out of 657 papers, 1.2%). While we are aware that research on Baltic Sea socio-economic benefits does exist, the link with ecosystems providing the service is mostly missing. To close this knowledge gap, we need a better analytical framework that is capable of directly linking existing quantitative information about ecosystem service generation with human benefit.