Lethal and sublethal effects of marine heatwaves on octocorals early life history stages

In this study, the effect of increased water temperature (+4 ºC and +6 ºC above ambient, 20 ºC) on larval survival and settlement was evaluated for two of the most representative Mediterranean octocoral species (Eunicella singularis and Corallium rubrum). Moreover, data on larval biomass and caloric consumption of larvae per day are also provided.Our study shows that warmer treatments did not affect the survival of symbiotic E. singularis larvae, but drastically reduced the survival of the non-symbiotic C. rubrum larvae. The results on larval biomass and caloric consumption suggest that higher mortality rates of C. rubrum exposed to increased temperature were not related to depletion of endogenous energy in larvae. The results also show that settlement rates of E. singularis did not change in response to elevated temperature after 20 days of exposure, but larvae may settle fast and close to their native population at 26 ºC (+6 ºC). Although previous experimental studies found that adult colonies of both octocoral species are mostly resistant to thermal stress, our results on early life history stages suggest that the persistence and inter-connectivity of local populations may be severely compromised under continued trends in ocean warming.