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Theme: Climate ChangeSynergistic effects of altered salinity and temperature on eelgrass (Zosteramarina) seedlings and adult plantsTiina Salo 1,2 & Morten Foldager Pedersen 11ENSPAC, Roskilde University, Universitetsvej 1, 4000 Roskilde, Denmark2Dept. of Biosciences, Åbo Akademi University, Artillerigatan 6, 20520 Åbo,FinlandEmail: tsalo@ruc.dkSalinity and temperature are some of the most important factors determiningeelgrass distribution and performance. Predicted climate changes areexpected to alter both salinity and water temperature in estuarine and coastalwaters. We investigated experimentally how the performance of seedlingsand adult plants was affected by the combined effect of altered salinity andtemperature. We conducted a 5-week experiment exposing eelgrass todifferent combinations of salinity (5, 12.5 and 20‰) and temperature (15,20 and 25°C). Both life stages responded negatively to lowered salinityand elevated temperature with seedlings being more sensitive than theadults. Altered salinity and temperature had synergistic effects on eelgrasssurvival and performance; high temperature in combination with low salinityresulted in higher mortality and lower number of leaves per shoot ascompared to situations where the salinity and temperature were closer toambient conditions. Sucrose concentrations in the leaves of both life stagesdecreased with decreasing salinity. Salinity and temperature affected theconcentrations of starch differently in seedlings and adult plants. Our resultsshow that altered salinity and temperature can have serious effects oneelgrass performance, especially when considering future climate scenarios.As seedlings appear to be more sensitive to stressors than adult plants,the future climate changes are likely to alter meadow population dynamicsemphasizing the higher importance of vegetative reproduction.- 34 -