Heterotrophy in parental coral colonies enhances larval survival independently of heat stress

Abstract Under the ongoing global change, a sustained reliance of symbiotic coral species on heterotrophy may support their resistance to climatic stressors. However, much remains unknown about the role of heterotrophy on coral reproduction, despite its key role in the persistence of coral populations and connectivity. In this study, we experimentally investigated how heterotrophic feeding of parental colonies of a symbiotic gorgonian may affect the larval release and their survival and settlement rates under both optimal and heat stress temperatures. A one-week delay in larval release in absence of heterotrophic inputs highlights its significant contribution to the gametogenesis. Moreover, heterotrophy also plays a crucial role in sustaining larval survival, as low-quality or smaller eggs produced in absence of heterotrophic inputs lead to significantly higher mortality of the resulting larvae, independently to their exposure to natural or warming temperatures. Overall, this study contributes to increase our understanding of the broader consequences of global change on coral populations under the globally forecasted reduction of primary production and zooplankton abundance.