Meeting Abstract
Although widely studied, aspects of coral bleaching remain poorly understood. It is generally agreed that perturbation causes the impairment of photosynthesis of symbionts (Symbiodinium spp.) and that this is the first step of bleaching. In what can be referred to as the canonical pathway, this is followed by an increase in reactive oxygen species, and cell and symbiont death. Alternatively, impaired photosynthesis also triggers a “non-canonical” pathway involving symbiont migration within the colony. In this pathway, damage to photosynthesis removes a major sink for carbon dioxide and bicarbonate, resulting in relatively higher levels of both. In some corals, gastrovascular flow and hence symbiont movement is driven mainly by cilia. In many systems, bicarbonate is known to activate ciliary action via soluble adenylyl cyclase (sAC) and cyclic adenosine monophosphate (cAMP). It remains an open question whether or not this pathway operates in corals. To test this, colonial octocorals were treated with bicarbonate and gastrovascular flow rates were calculated. When treated with a low concentration of bicarbonate for a short period of time there was little to no effect on flow rates. However, when treated with a higher concentration for a longer period of time flow rates were dramatically enhanced. To further examine this pathway, additional experiments will include treating corals with an inhibitor of sAC and assaying cAMP levels. These results for the first time connect basic coral physiology with carbon dioxide levels in the ocean. Greater migration of symbionts may result in more symbionts exiting the coral colony or reaching “safe zones” in a colony where they can survive perturbation.
