A new study has shown that bristleworms and bacteria can be linked to bleaching in certain species of corals.
According to new research published by Rosenberg and Falkowitz in the journal Annual Reviews in Microbiology, the coral Oculina patagonica undergoes seasonal bleaching during the summer when sea temperatures rise due to the bacteria Vibrio shiloi.
The bristleworm, Hermodice carunculata, acts as a reservoir for Vibrio shiloi during the winter, and serves as a vector for the bleacing disease during the spring and summer when the water gets warmer.
Rosenberg and Falkowitz say that V. shiloi causes bleaching by adhering to a receptor containing galactoside in the coral mucus. The bacteria then penetrates into the cells of the coral epithelium and differentiates to form a peptide toxin containing high levels of the amino acid proline. This inhibits photosynthesis in the corals' zooxanthellae which causes them to bleach.
For more details on the research see the paper: Rosenberg E, Falkovitz L. (2004) - The Vibrio shiloi/Oculina Patagonica Model System of Coral Bleaching. Annu Rev Microbiol. 2004