The First Proof of Concept Demonstration of Nanowarming in Coral Tissues

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.