The gut within: reframing the coral gastrovascular cavity as a discrete anaerobic microbial ecosystem

ABSTRACT Coral holobionts are typically studied at colony or fragment scale, erasing the spatial context of the microenvironments which microbial life occupies. Recent microsensor work (Q. Zhang, E. Bollati, and M. Kühl, Appl Environ Microbiol 92:e02441-25, 2026, https://doi.org/10.1128/aem.02441-25 ) shows the coral gastrovascular cavity (GVC) sustains active anaerobic metabolism, reflecting patterns of symbiotic state and heterotrophic feeding. These findings recast the GVC as a discrete, gut-like ecosystem with its own redox regime, substrate supply, and bacterial community, calling for spatially explicit approaches in coral research to resolve metabolism at microscopic scales.