Seagrasses are important foundation species, which support high coastal biodiversity and provide many socioeconomic benefits. However, seagrasses are threatened by anthropogenic changes, both climate and non-climate related, for example, marine heatwaves (MHWs) and concurrent light limitation from eutrophication or increased sedimentation. In this experiment, we exposed the tropical seagrass Halophila ovalis to a 10-day MHW and three light intensities to examine the impacts on multiple levels of organisation, i.e. the growth, productivity, nitrogen cycling, and leaf microbiome of the seagrass. We showed that MHWs and light limitation can drive decreased seagrass growth, chlorophyll concentration and cause shifts in the leaf microbial functional groups, although there was little interaction between stressors. It is therefore important that good water clarity and habitat health is maintained to reduce the susceptibility of seagrasses to extreme climatic events.
 

seagrass ecosystems, multiple stressor, marine heatwaves, light limitation