Steps Toward Vitrification and Banking of Coral Larvae Using Field‐Friendly Cryomesh Technology

Coral reefs are declining globally, and novel solutions, such as cryopreservation, can help secure coral biodiversity and genetic diversity. Factors that affect successful cryopreservation of coral larvae include cryoprotectant type and concentration, membrane permeability, larval developmental stage, lipid content, volume, and freezing and warming rates. This study examined conduction-dominated "cryomesh" technology across a range of coral species, distinguishing vitrification on cryomesh, 24 h swimming survival, and settlement competence as separate measures of success. Using a previously successful cryoprotectant solution, the exposure time, volume, and developmental stage most amenable to cryomesh cryopreservation were examined, and biophysical attributes were modeled to determine cooling and rewarming rates. Most species vitrified on the cryomesh and showed short-term motility, but robust 24 h swimming survival was limited to Lobactis scutaria and Fungia fungites, the smallest species; other small-volume species did not survive. To improve heat transfer, subsets of embryos were sheared during early development, yielding sub-size larvae that did not swim post-thaw, but the sheared, untreated controls settled and matured normally. These findings show that volume alone does not ensure survival. Additional next steps must include toxicity and permeation studies of other cryoprotectants and long-term restoration potential evaluated by examining post-thaw settlement success.