Coral reef decline raises concerns about potential co-extinctions of coral-associated fauna that rely on corals for survival. Despite their diversity and abundance on reefs, these typically small symbiont species have received little attention regarding their vulnerability. The thesis of Henrique Bravo Gouveia investigated symbiont-coral relationships in the Caribbean region, which harbours around 70 described coral species and a similar number of known associated symbionts.

The main hypothesis examined throughout this thesis was that if coral hosts were to disappear, so would the species that obligately depend on them. However, determining co-extinction risks is challenging due to varying host specificity levels among symbionts. The research highlighted here advanced our understanding of the biology, ecology, and genetics of certain symbiont species like the elkhorn coral crab (Domeciidae) and gall crabs (Cryptochiridae), which could then in turn be used to understand more about the host-symbiont relationship.

The methodologies employed ranged from genetics, to genome characterization, stable isotopes, sampling estimation, and the building of an ecological network. This latter method mapped host-symbiont interactions in Curaçao, allowing for the simulation of coral extinction events. These simulations revealed an already impacted network and identified critical coral hosts fundamental for symbiont persistence.Although our understanding of these systems lags behind the rate of coral degradation, this research contributes valuable knowledge about potentially threatened associated fauna, and provides insights into coral species that could prove key for supporting symbiont biodiversity.