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Recovery of Palau's Coral Reefs After the ENSO-Induced Bleaching Event of 1998
Golbuu, Y., Victor, S., Penland, L., Idip Jr., D., Emaurois, C., Okaji, K., Yukihira, H., Iwase, A. and van Woesik, R. 2007. Palau's coral reefs show differential habitat recovery following the 1998-bleachng event. Coral Reefs 26: 319-332.

The authors state that "documenting successional dynamics of coral communities following large-scale bleaching events is necessary to predict coral population responses to global climate change," and that a good opportunity to do so is presented by Palau (Micronesia), since "in 1998, high sea surface temperatures and low cloud cover in the western Pacific Ocean caused high coral mortality of the outer exposed reefs of Palau."

What was done
Golbuu et al. examined recovery rates of coral communities on the Palauan reef complex (7°30'N, 134°30'E) at two depths (3 and 10 m) at several different sites (nine outer-reef wave-exposed sites, four on the east coast and five on the west coast; two patch reef sites; and two sheltered-bay sites) 3, 4 and 7 years after the 1998 El Niņo-Southern Oscillation (ENSO)-induced bleaching event, which they conducted in late 2001 to early 2002, late 2002 to early 2003, and late 2004 to early 2005, respectively.

What was learned
The nine researchers report that "coral populations recovered rapidly on the reefs of Palau," but that "recovery trajectories changed over time and were habitat and depth-dependent," noting that "seven years after the bleaching event, some reefs supported >30% coral cover, and some habitats supported >40% coral cover." In addition, they say that "recovery within the bays at 3 m was mostly a consequence of growth of remnant (surviving) coral colonies, while recovery on the exposed slopes was mostly likely a consequence of both remnant regrowth and sexual recruitment events at 10 m, and more a consequence of recruitment at 3 m."

What it means
In discussing their results, Golbuu et al. write that "the recovery on some of Palau's reefs was similar to, albeit less rapid than, recovery on a lava flow reported by Tomascik et al. (1996)," in which "remarkable coral community development" occurred "on a bare andesitic lava substrate following a major volcanic eruption in the Banda Sea, Indonesia," where "in five years, coral coverage averaged over 60%, supporting 124 coral species." They also cite Guzman and Cortes (2001) in this regard, noting that the latter two researchers had found that "populations of massive and branched corals in 1997-1998 were more tolerant to elevated thermal stress than populations in 1982-1983 [when another ENSO-induced period of high sea surface temperatures occurred] in Costa Rica, where both events recorded similar warming trends and temperature maxima," which observations led the two scientists to suggest that over the time period between the two events, the region's corals "had adapted to these warmer conditions." Similar observations are reported by Golbuu et al. to have been made by van Woesik et al. (2004) in southern Japan, and by Glynn et al. (2001) in Panama and Ecuador. The importance of this growing body of work is that it demonstrates the strong potential for recovery from coral bleaching at various places around the world, with perhaps an evolving potential for corals to successfully recover from increasingly more intense warming episodes in the face of rising global temperatures.

Glynn, P.W., Mate, J.L., Baker, A.C. and Calderon, M.O. 2001. Coral bleaching and mortality in Panama and Ecuador during the 1997-1998 El Niņo-Southern Oscillation event: spatial/temporal patterns and comparisons with the 1982-1983 event. Bulletin of Marine Science 69: 79-109.

Guzman, H.M. and Cortes, J. 2001. Changes in reef community structure after fifteen years of natural disturbances in the eastern Pacific (Costa Rica). Bulletin of Marine Science 69: 133-149.

Tomascik, T., van Woesik, R. and Mah, A.J. 1996. Rapid coral colonization of a recent lava flow following a volcanic eruption, Banda Islands, Indonesia. Coral Reefs 15: 169-175.

Van Woesik, R., Irikawa, A. and Loya, Y. 2004. Coral belaching: signs of change in southern Japan. In: Rosenberg, E. and Loya, Y. (Eds.) Coral Health and Disease. Springer, Berlin, Germany, pp. 119-141.

Reviewed 21 November 2007