LEWIS, C.L.*; COFFROTH, M.A.; University at Buffalo, NY; University at Buffalo, NY: Changing horses in mid stream: Secondary xoozanthellae uptake by the Caribbean octocoral Briareum asbestinum following an experimentally induced bleaching event

Coral bleaching events are typically characterized by the breakdown of the coral-algal symbiosis and the loss/expulsion of the algal symbionts (ie, zooxanthellae). After a bleaching event, corals often re-establish their symbiotic zooxanthella population. Reconstituted zooxanthella populations are generally believed to derive from some combination of zooxanthella cells that remained in the host and newly acquired cells. However, the actual source of these zooxanthella symbionts has yet to be established. In this study we examined whether adult colonies of the octocoral B. asbestinum were capable of secondarily acquiring zooxanthella from the environment. Zooxanthella populations within healthy colonies were genetically characterized based on their chloroplast 23S r-DNA (cp-genotype). These colonies were then induced to bleached by maintaining them in a darkened tank for 10-12 weeks. Zooxanthella genotype was reassessed at the end of the bleaching period. The bleached colonies were then placed in aquaria subject to natural lighting and inoculated with cultured zooxanthellae that had a rare cp-genotype. Subsequent chloroplast genotyping of the zooxanthellae within the B. asbestinum colonies revealed the presence of zooxanthellae identical to the specific zooxanthellae cultures used for inoculations. This is the first demonstration that octocorals are capable of secondarily acquiring zooxanthellae as adults.