Stability of symbiotic dinoflagellate type in the octocoral briareum asbestinum

Coral bleaching - the loss of photosynthetic algal symbionts from their cnidarian hosts - can lead to coral mortality and subsequent reef degradation. To understand the phenomenon of coral bleaching it is imperative to understand natural fluctuations in symbiotic dinoflagellate diversity and density. In this study, Symbiodinium type, based on length variation in domain V of the chloroplast large subunit of rDNA (cp23S rDNA), and cell densities were followed in 2 populations of the octocoral Briareum asbestinum over 1 yr. Symbiodinium type varied little over the course of the study despite anomalously cold sea surface temperatures during January 2003, when B. asbestinum populations experienced a significant loss of symbionts. This provides some of the first evidence that Caribbean octocorals are susceptible to cold-water bleaching events. Furthermore, the symbiont stability observed within B. asbestinum contributes to an increasing number of studies suggesting that many zooxanthellate coral species may not respond to fluctuating environments by changing symbionts.