Assessing the impacts of cryopreservation on the mitochondria of a thermotolerant Symbiodinium lineage: Implications for reef coral conservation

Abstract

Earth's coral reefs are threatened by a barrage of anthropogenic insults, and cryopreservation-based conservation measures are warranted. Successfully cryopreserved corals could then thawed and out-planted on reefs when ocean temperatures stabilize. In such efforts, it will be necessary to also cryopreserve the photosynthetic dinoflagellates (genus Symbiodinium) that reside within the corals' gastrodermal cells. Given this need, Symbiodinium (clade D) cells were cryopreserved in 2 M propylene glycol by a two-step freezing protocol herein and then cultured for 42 days post-thaw. To gauge the effect of cryopreservation, mitochondrial DNA content and intracellular ATP concentration were assessed, and the former parameter was nearly 2-fold higher in freeze-thawed cells compared to controls after 14 days of post-thaw culture. In contrast, intracellular ATP concentration was relatively lower in freeze-thawed cells after seven days of post-thaw culture, though returned to control levels in samples cultured for 42 days post-thaw.

Keywords: ATP; Coral reef; Cryopreservation; Mitochondria; Symbiodinium.