"Blue" corals

[Hernandez Edwin A]

   During a mild bleaching event ocurred in the eastern coast of the
island of Puerto Rico, Caribbean Sea (approx. 18N, 65W) during 1992, I
observed a 60 cm diameter colony of Siderastrea siderea with a pale grey
coloration and showing nearly round 5 cm diameter blue spots.  This
ocurred at Candelero Beach, Humacao, at 1.5 m depth.  The coral recovered
its normal color within two months approximately.  By that moment, I was
told by the late Dr. Carlos Goenaga (University of Puerto Rico, Dept.
Biology, Mayaguez Campus) that he did also see several colonies of S.
siderea showing similar blue spots.

  During a routine dive on September 1997, while monitoring coral reefs at
Cayo Diablo, a small key located at 11 km off NE Puerto Rico, within the
boundaries of La Cordillera Natural Reserve, I saw two colonies 70-80 cm
in diameter of S. siderea showing a similar pattern as described above.
The interesting aspect of that event was that the colonies first started
showing a pale coloration.  Two weeks later they became even more paler
(pale grey) and were showing these blue tones.  Both of them receovered
their normal color.  This also happened during a mild bleaching event
which affected several other scleractinians and Millepora.  Both coral
heads were located at approx. 7 m in depth.

   By the end of April and early May of this year we detected what appears
to be the early signs of a bleaching event.  Some S. siderea colonies have
started to become pale within or very close to one of our monitoring
quadrat grids in Culebra Island, located 27 km off eastern Puerto Rico.
However, there were no signs of blue tones.  These are located at depths
ranging from 4 to 8 m.

   I'm not sure where do this blue color comes from but I suspect it might
be a kind of residual color of the polyp tissue following the loss of
zooxanthellae or the loss of other pigments.  Particularly, it would be
interesting to study the possibility that this might be due to
autofluorescent pigments?????  These are fairly common in deep water
colonies and their basic job is to convert deep blue and purple
wavelengths (common at deeper habitats) to other wavelengths that can be
readily used by zooxanthellae (just as if the corals were living in
shallower environments). Are these pigments more resistant to
bleaching??? This should be something very interesting to document.
Please, keep me posted on this.  Good luck!

Sincerley,

Edwin A. Hernandez
University of Puerto Rico
Department of Biology
Coral Reef Research Group
P.O. Box 23360
San Juan, Puerto Rico 00931-3360