Meeting Abstract
Coral bleaching (the loss of the algal symbionts) due to increased sea surface temperatures has led to increased mortality of many scleractinians. Although reports of bleaching among octocorals is less common, extensive octocoral bleaching was observed in the Florida Keys during 2014 and 2015. We monitored Symbiodinium type and densities in three octocoral species across the 2015 bleaching event (May 2015-May 2016) to investigate severity of bleaching. Individual colonies of Muricea atlantica, Muricea elongata, and Plexaurella dichotoma on two reefs were tagged and cell densities and symbiont type for each species were monitored over the course of the event. Cell densities were significantly different between months, with the lowest densities occurring in September. Based on cell counts, as well as visual observations, M. atlantica and P. dichotoma colonies were more severely bleached than Muricea elongata. Preliminary results indicate that each host species harbored strains within the Symbiodinium B1-ITS phylotype. Based on 4 microsatellite loci these species harbor at least 3 (M. atlantica) , 9 (M. elongata) and 3 (P. dichotoma) symbiont genotypes and genotypes were not shared between host-species. Little mortality was observed within any host species through May 2016, and in the majority of corals symbiont genotypes did not change across the bleaching event. These studies are ongoing and additional samples from 2016 and 2017 will be examined to establish a baseline in non-bleaching years. Bleaching tolerance could not be clearly explained by the coral species or the symbiont type independently, and it is possible that both parties play a role in bleaching resistance.
