Predicting the combined effects of warming and nutrient increase on the tropical seagrass Halophila stipulacea

3rd Israel Conference for convervation Science (ICCS),Tel-Aviv, 18-20th October 2022Famous for its coral reefs, the Gulf of Aqaba also supports extensive seagrass meadows, dominated by Halophila stipulacea. Nutrient loading and warming are considered the biggest threats to seagrass meadows, and their combination can potentially amplify their negative effects. We exposed two seagrass populations with different eutrophication “history” to control (27ºC) and simulated warming (31ºC), with and without nutrients (20 μg DIN). While exposure to only thermal stress favoured growth, eutrophication only reduced Fv/Fm and growth but favoured algae proliferation. Combined effects negatively enhanced seagrass performance with the highest mortality rates observed after four weeks of combined exposure. Negative effects of combined stressors were stronger in populations with low eutrophication “history”. Lipidomic analyses showed stress decreased ratios of fatty acids 16:3n-3/16:2n-6 and 18:3n-3/18:2n-6 with bigger declines in these ratios following exposure to the interaction of both stressors. The GoA’s waters are warming faster than the average of the world’s coastal warming trends. While it might be difficult to directly control the effects of global warming, sources of eutrophication are usually on local scales. For seagrasses to survive climate change, managers must put efforts into limiting other stressors such as eutrophication which would reduce the resilience of meadows to other stressorsN