A qualitative survey was performed at Enrique and Media Luna Reefs from 29-31 July 2008 near La Parguera, Puerto Rico. Bleaching was nearly non-existent with only a few colonies of Palythoa caribaeorum displaying visually discernible bleaching as shown in the image on the left. Several colonies of Siderastrea siderea displayed evidence of paling and discoloration from their normal brownish-gray hues to shades of dark pink and blueish brown. This is likely a result of the normal, seasonal summer declines in zooxanthellae densities within the coral host and not indicative of a bleaching event.
On the north side of Media Luna Reef (east of the ICON pylon) there were high abundances of urchins (Echinometra viridis and E. lucunter -- it is likely that both species were present, but E. viridis appeared to be more abundant). In the images above it is clear that these urchins are bioeroding some dead coral heads through their feeding activities. Urchins graze upon turf and macroalgae that grows upon reefal carbonate substrates and in doing so chew-up some of the reef. This is totally natural and erosion rates are usually less than the rates at which new carbonate is produced by corals and calcareous algae. However, population booms of urchins were observed in the eastern Pacific following the mass coral mortality that occurred as a result of bleaching due to thermal anomalies associated with the 1982-83 El Nino-Southern Oscillation. These increases in urchin abundances were shown to rapidly erode reefs in some areas of the eastern Pacific. It is believed that the large amount of bare substrate which opens up on reefs following mass coral mortality events facilitates the recruitment of urchin larvae by 1) creating more appropriate habitat space for urchin larvae to settle and 2) causing an increase in algae that grows upon this bare space and provides more food for the urchins. These population booms eventually "snuff themselves out" by overgrazing all of the algae available, making them resort to feeding on the less nutritious crustose corraline algae (CCA) and then the actual reef framework itself, which has little if any nutritional value. In the end, many of the urchins will simply starve to death, but in the process can rapidly destroy in tact reef framework structures. Fortunately, these very high urchin abundances appear restricted to very shallow water on the north side of Media Luna. Echinometra was observed around the ICON pylon and on Enrique Reef, but their abundances did not appear to be unnatural. These high (albeit localized) abundances of urchins three years after the Caribbean-wide bleaching event suggest that this phenomenon may be a characteristic of post-bleaching/mortality reef dynamics. It will be interesting to see if urchins go through boom/bust population dynamics anywhere else in the Caribbean, or if this is isolated to SW Puerto Rico.
A beautiful Porites furcata reef was observed by Dr. James Hendee and myself on the east side of Media Luna Reef proximal to the area of intense bioerosion noted above. Live coral cover was very high and mono-specific in this area. These adjacent accretional and erosional environments illustrate the highly dynamic variability of calcium carbonate production and loss that can occur on reefs over short distances.
Dr. James C. Hendee and myself observed a potential back-up site for the planned MAP-CO2 buoy just west of Media Luna Reef, but sill east of the ICON pylon. This is a mostly dead Montastraea annularis reef that occurs in the lee of Media Luna. However, there are patches of living M. annularis re-colonizing some of the dead reef surface.
Best regards,
Derek P. Manzello