Over the last decades, Fucus vesiculosus, an ecologically important macroalga in the German Baltic Sea, has shown a massive retreat from the deeper zones of its former distribution presumably due to low light co-acting with other potential stressors such as high temperature, fouling, and grazing. In shallow water F. vesiculosus may be exposed to high water temperatures during summer seasons. Intensity and frequency of heat waves are expected to increase due to climate change which could potentially affect all fucoid life stages. Early life stage processes (fertilization, germination) are often considered particularly sensitive to stress. If the mortality caused by a first heat wave in a genetically diverse population selects for stress resistance, we would expect the survivors to be less sensitive to a second heat wave or possibly even to other stressors like feeding pressure.
In the present study, the mortality of early post-settlement stages of F. vesiculosus under thermal stress and the sensitivity of survived recruits against a proximate stressor (feeding pressure, second heat wave) were analysed by laboratory experiments. The mortality of early fucoid life stages at 25°C, compared to their mortality at 15°C was significantly higher. Regrettably, the ensuing assessment of feeding impact by Idotea baltica and Hydrobia ulvae on the surviving germlings could not be analysed since the two consumer species unexpectedly avoided feeding on the young stages of F. vesiculosus. During the second thermal stress experiment fucoid offspring which was genetically preselected by high temperature (first heat wave: 25°C) differed not significantly in sensitivity from fucoid offspring without prior stress.
Information about possible changes of extreme wave heights are essential for the future safe design of coastal and flood protection structures likes dykes, flood protection dunes, revetments etc. In this study, scenarios of regional climate change up to 2100 are used for the evaluation of changes of wave conditions. Analyses on calculated significant wave heights derived from extreme value statistics are showing a different signal of change for the selected locations along the German Baltic Sea Coast. The results are showing that extreme wave heights with a return level of 200 years can increase up to +14%. But also a decrease of down to -14% were found compared to actual conditions, depending on the location and climate change scenario applied. At the location of Warnemünde a slight increasing trend for the change of extreme wave heights could be found for 3 of 4 scenario runs with a maximum increase of +7%.