[Coral-List] Coral disease or bleaching??

[Allan Bright]

For those who are interested, I too have observed these ring shaped
bleached spots on colonies of Acropora palmata in St. Thomas and St.
John, USVI.  I conducted monthly surveys of A. palmata colonies at
five sites around the two islands from September 2007 through July
2009.  During this survey period, I noticed this pattern of bleaching
on 12% of my regularly monitored colonies (condition observed
year-round).  On a few colonies the bleached spots were observed every
month during the survey period (one colony of which contained a
Microspathodon chrysurus territory).  The general characteristics of
the pattern I observed are a ring/circle (~2cm diameter) of thin,
bleached tissue with the corallites appearing worn down.  The bleach
spots generally occurred in great numbers, sometimes leaving large
areas of the colony bleached.  No tissue loss was observed as a result
of this condition, with the exception of one colony where tissue loss
occurred post-bleaching (after approximately 7 months of condition
observed to be present).  From my observations, it appears as though
damselfish are repetitively nipping at particular areas of the colony
resulting in this bleaching pattern.  On two occasions I have
witnessed the yellowtail damsel, Microspathodon chrysurus, nipping at
these small bleach spots.

Photo examples can be found at the following link (my apologies for
the poor image quality):
http://s848.photobucket.com/albums/ab47/allanjbright/?action=view&current=bleachspots.jpg


Williams et al. (2006) also suggest damselfish as possible cause of
bleached rings on colonies of A. palmata.

Williams, D.E., M.W. Miller, and K.L. Kramer. 2006. Demographic
monitoring protocols for threatened Caribbean Acropora spp. corals.
NOAA Technical Memorandum NMFSSEFSC-543. 91 pp.

regards,
Allan Bright