From: "Fernando A. Zapata Rivera" <fazr@biologia.univalle.edu.co
To: Coral-List <coral-list@coral.aoml.noaa.gov
Subject: Coral Bleaching in the TEP

CORAL BLEACHING IN THE TROPICAL EASTERN PACIFIC

        Regarding the recent report on coral bleaching in the 
Pacific coast of Panama made recently in this list by Baker, 
Mat, and Glynn, I would like to share my own observations 
from the Pacific coast of Colombia.
        During the course of ongoing studies on coral reefs of Gorgona Island (2 58 N, 78 10 W) being carried out by two teams from Universidad del Valle, I have made three visits to the island between May 24 and September 16, 1997. During the first visit (May 24-29), I made extensive, albeit non-quantitative, observations on coral cover and "health" at six different reef sites around the island, and did not observe any sign of significant or widespread coral bleaching. However, my colleague Jaime
Cantera did call my attention to the whitened, most distal portion of
branches of  some patches of Pocillopora sp., which he interpreted as coral bleaching (the lower portion of colonies had normal coloration). To me this was not different to the usual whitened branch tips normally seen in the Pocillopora capitata species "complex". On the other hand, I did observed a very small number of partially to completely bleached colonies of Pocillopora sp., but these were always unattached, large fragments and seemed to have suffered from some unknown physical disturbance. Thus, I did not attribute this bleaching to sea water warming. Sea surface
temperature remained constant throughout our visit at 29 degrees celsius.
        During the second visit (July 27-August 1) I made observations at four sites and only in the two largest reefs I saw some signs of bleaching. These were similar to the bleaching observed during the first visit, except that the number of large, unattached fragments of Pocillopora sp. that were bleached was more noticeable (i.e., it appears that the number of bleached fragments had increased). I also found one small (15 cm diameter), unattached colony of Pavona varians completely bleached, without live tissue, and with beginning algal overgrowth. At that time it again seemed to me that these cases of bleaching could not be
attributable to sea warming. Occasional SST measurements made revealed that water temperature was 29 degrees.
        During the last visit (September 10-16) it became apparent that a bleaching episode was on its way based on observations at the two major reefs of Gorgona. The bleaching at the branch tips of Pocillopora sp. was now more obvious, extending downward about 2 cm from the tip, and patches with this type of bleaching at the tips were encountered frequently. These patches appear to be monospecific judging from colony morphology and coloration, and were surrounded by high cover of other, normal looking Pocilloporids, suggesting that some species of Pocillopora are more susceptible than others to bleaching. I believe that bleaching at the tips of branches was not caused by aerial exposure during extreme low tides (which causes similar bleaching) since it was observed in both shallow and deeper sites on the reef, and some normal-looking patches were located next to and at the same depth as bleached patches. No algal growth was yet apparent at the bleached tips of branches on any of these coral patches. Additionally, partial bleaching was now readily seen on species of massive corals (large Pavona gigantea, and P. clavus). Some colonies had up to 30% of their surface bleached. Nonetheless, the extent of coral bleaching at the scale of an entire reef was clearly low, although it was not quantified. Water temperature measurements made varied between 28 and 29.5 degrees.
        The main point I would like to make is that there appears to be a trend towards increased bleaching with time as SST is maintained abnormally high. According to Dr. Alan Strong's "Hotspots maps" (see http://wesley.wwb.noaa.gov/eileen/orad/const1.html),

---- now at: http://manati.wwb.noaa.gov/orad 
     link to "Experimental Products" & "HotSpots" ---

 SST at Gorgona was at least 2.5 degrees celsius above the norm on the week of August 11, 1997.  Whether this trend continues at Gorgona remains to be seen, but it is interesting that significant bleaching is already being reported elsewhere in the tropical eastern Pacific.

Fernando Zapata