Coral reefs demonstrate considerable biological diversity and are critical to humans. However, these fragile ecosystems are currently threatened by the onslaught of anthropogenic stressors; this may result in the extinction of numerous coral species in the near future. Cryopreservation is a long-term storage technique that uses low temperatures to keep cells and tissues alive in a quiescent state. In this study, the gorgonian corals Junceella fragilis and J. juncea were target species; their oocytes were cryopreserved using a controlled, slow-cooling protocol. Results revealed that the effective cooling rate and eutectic temperature were respectively 10°C/min and -50°C for J. fragilis oocytes and 5°C/min and -40°C for J. juncea oocytes. For J. fragilis and J. juncea oocytes, addition of 1 M methanol with sucrose resulted in little improvements on the viability and morphology for freezing. Moreover, methanol supplemented with lipids led to better oocyte viability and reduced the percentage of damaged oocytes. Overall, the oocyte viability and morphology were better on J. juncea than for J. fragilis under various treatments conducted in this study. This study represents the first systematic assessment of controlled slow-cooling parameters, including cooling rates, cryoprotective agents, and equilibration conditions, for coral oocyte cryopreservation.
Cryopreservation, Coral oocytes, Controlled slow freezing, Lipid, Sugars