Cryobiology of coral fragments

Around the world, coral reefs are dying due to human influences, and saving habitat alone may not stop this destruction. This investigation focused on the biological processes that will provide the first steps in understanding the cryobiology of whole coral fragments. Coral fragments are a partnership of coral tissue and endosymbiotic algae, Symbiodinium sp., commonly called zooxanthellae. These data reflected their separate sensitivities to chilling and a cryoprotectant (dimethyl sulfoxide) for the coral Pocillopora damicornis, as measured by tissue loss and Pulse Amplitude Modulated fluorometry 3 weeks post-treatment. Five cryoprotectant treatments maintained the viability of the coral tissue and zooxanthellae at control values (1 M dimethyl sulfoxide at 1.0, 1.5 and 2.0 h exposures, and 1.5 M dimethyl sulfoxide at 1.0 and 1.5 h exposures, P > 0.05, ANOVA), whereas 2 M concentrations did not (P < 0.05, ANOVA). A seasonal response to chilling was observed in the coral tissue, but not in the zooxanthellae. During the winter when the fragments were chilled, the coral tissue remained relatively intact (∼25% loss) post-treatment, but the zooxanthellae numbers in the tissue declined after 5 min of chilling (P < 0.05, ANOVA). However, in the late spring, coral tissue (∼75% loss) and zooxanthellae numbers declined in response to chilling alone (P < 0.05, ANOVA). When a cryoprotectant (1 M dimethyl sulfoxide) was used in concert with chilling it protected the coral against tissue loss after 45 min of cryoprotectant exposure (P > 0.05, ANOVA), but it did not protect against the loss of zooxanthellae (P < 0.05, ANOVA). The zooxanthellae are the most sensitive element in the coral fragment complex and future cryopreservation protocols must be guided by their greater sensitivity.