The increasing rate of global warming predicted for the coming decades will significantly impact coastal ecosystems. Habitats of particular concern in light of the predicted temperature increase are seagrass meadows, which are sensitive indicators of coastal and estuarine health. Another potential threat to seagrasses are pathogens. Pathogens are present in seagrasses around the world and have been responsible for large seagrass losses in the past. In the Mediterranean, the presence of pathogenic organisms in seagrass tissue has not yet been shown to increase seagrass mortality, but it is thought that pathogens pose a significant risk of seagrass decline under deteriorating environmental conditions. While recent efforts have been made to examine the effects of increasing temperature on seagrasses, the occurrence of pathogens is not well studied, and we know little of what combined effects these stressors may produce. In this proposal, I use seagrasses, a recognized sensitive indicator of environmental change, to develop a first effort at evaluation of future global scale changes that result from interactions of temperature and a pathogenic protist Labyrinthula sp. The hypothesis to be tested in this project is that increased temperature makes seagrasses more vulnerable to pathogens and that the combined effects of pathogenic infection and warming would be additive and cause seagrass mortality at lower temperatures than is observed for healthy seagrasses. I will carry out a field study and a series of laboratory experiments to examine the interactive effects of warming and pathogens.