Carbon budget trends in octocorals: a literature review with data reassessment and a conceptual framework to understand their resilience to environmental changes

Although octocorals are a key component of marine hard-bottom systems, their feeding performance is still poorly understood. Understanding carbon budget trends in octocorals’ feeding ecology seems essential to assess their role in benthic–pelagic coupling and to predict their responses to environmental changes. Herein, we provide a review of the feeding ecology of octocorals and an overall data reassessment of their carbon budgets through a systematic and comprehensive search of peer-reviewed literature published between 1960 and 2020, highlighting knowledge gaps. Overall, the feeding ecology of more than 95% of octocoral species remains unknown. Based on the available data, suspension feeding accounts for 162.8 ± 171.0% of the metabolic requirements in azooxanthellate octocorals and 28.7 ± 32.3% in zooxanthellate octocorals. Autotrophy is responsible for 156.7 ± 113.9% of the acquired carbon in zooxanthellate octocorals. However, this value is significantly lower in gorgonian phenotypes compared to other soft corals. We present a conceptual framework describing and exploring the most relevant hypotheses regarding putative advantages of octocorals over scleractinians against environmental changes, including their ability to decrease energy expenses to overcome stress events, their lower dependency on autotrophy, and the type of interaction (facultative and flexible) with their symbionts.