Seasonal Preservation Success of the Marine Dinoflagellate Coral Symbiont, <i>Symbiodinium sp</i>.

<div><p>Coral reefs are some of the most diverse and productive ecosystems on the planet, but are threatened by global and local stressors, mandating the need for incorporating <i>ex situ</i> conservation practices. One approach that is highly protective is the development of genome resource banks that preserve the species and its genetic diversity. A critical component of the reef are the endosymbiotic algae, <i>Symbiodinium sp</i>., living within most coral that transfer energy-rich sugars to their hosts. Although <i>Symbiodinium</i> are maintained alive in culture collections around the world, the cryopreservation of these algae to prevent loss and genetic drift is not well-defined. This study examined the quantum yield physiology and freezing protocols that resulted in survival of <i>Symbiodinium</i> at 24 h post-thawing. Only the ultra-rapid procedure called vitrification resulted in success whereas conventional slow freezing protocols did not. We determined that success also depended on using a thin film of agar with embedded <i>Symbiodinium</i> on Cryotops, a process that yielded a post-thaw viability of >50% in extracted and vitrified <i>Symbiodinium</i> from <i>Fungia scutaria</i>, <i>Pocillopora damicornis</i> and <i>Porites compressa</i>. Additionally, there also was a seasonal influence on vitrification success as the best post-thaw survival of <i>F</i>. <i>scutaria</i> occurred in winter and spring compared to summer and fall (P < 0.05). These findings lay the foundation for developing a viable genome resource bank for the world’s <i>Symbiodinium</i> that, in turn, will not only protect this critical element of coral functionality but serve as a resource for understanding the complexities of symbiosis, support selective breeding experiments to develop more thermally resilient strains of coral, and provide a ‘gold-standard’ genomics collection, allowing for full genomic sequencing of unique <i>Symbiodinium</i> strains.</p>