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Abstract Corals are under siege by both local and global threats, creating a worldwide reef crisis. Cryopreservation is an important intervention measure and a vital component of the modern coral conservation toolkit, but preservation techniques are currently limited to sensitive reproductive materials that can only be obtained a few nights per year during spawning. Here, we report the successful cryopreservation and revival of cm-scale coral fragments via mL-scale isochoric vitrification. We demonstrate coral viability at 24 h post-thaw using a calibrated oxygen-uptake respirometry technique, and further show that the method can be applied in a passive, electronics-free configuration. Finally, we detail a complete prototype coral cryopreservation pipeline, which provides a platform for essential next steps in modulating post-thaw stress and initiating long-term growth. These findings pave the way towards an approach that can be rapidly deployed around the world to secure the biological genetic diversity of our vanishing coral reefs. 

Abstract Coral reefs are threatened by anthropogenic climate change, which causes ocean acidification and warming that can result in coral death and the loss of genetic diversity on reefs around the world. Global efforts to secure the genetics of threatened populations using cryopreservation and biobanking are underway but are limited to coral sperm and larvae, available only during brief annual spawning events. Methods to cryopreserve adult coral tissues to enable biobanking activities year‐round are urgently needed, but are challenging due to the presence of a calcium carbonate skeleton and algal symbionts within the tissues, and chill sensitivity. In this study, vitrification and laser nanowarming permitted successful recovery of adult coral tissues in a novel sample type, the single‐polyp microfragment. Fluorescence and confocal microscopy shows clearly defined green fluorescent protein auto‐fluorescence around the polyp mouth post‐warming, with an overall survival rate of 39.7 ± 7.4% at 24 h post‐warming and 23.3 ± 9.7% at 1 month, but relatively few algal symbionts are present in the tissues, indicating poor survival of these cells. These proof‐of‐concept results provide a basis for continued research and development of a field‐ready protocol for cryopreservation of adult coral tissues, which will be essential to prevent extinctions and support reef restoration.