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Recurrent Bleaching and Storms Need Not Spell "the End" for Earth's Corals
Adjeroud, M., Michonneau, F., Edmunds, P.J., Chancerelle, Y., Lison de Loma, T., Penin, L., Thibaut, L., Vidal-Dupiol, J., Salvat, B. and Galzin, R. 2009. Recurrent disturbances, recovery trajectories, and resilience of coral assemblages on a South Central Pacific reef. Coral Reefs 28: 775-780.

The authors write that "coral reefs are increasingly threatened by various disturbances, and a critical challenge is to determine their ability for resistance and resilience," noting that "most models predict an increase in the frequency and severity of disturbances over the next few decades." It is possible, of course, that those predictions may never come to pass; nevertheless, it is important to consider the natural ability of earth's corals to resist or recover from such challenges.

What was done
Focusing on coral reefs of the Tiahura outer reef sector at the western end of the north shore of Moorea, French Polynesia, which region, in their words, "is largely free of direct anthropogenic disturbances," Adjeroud et al. (2009) describe the results of detailed observations made there periodically since the early 1970s and annually since 1991, which history, according to them, "constitutes one of the longest records of coral reef dynamics."

What was learned
Concentrating on the period of detailed annual observations (1991 and onward), the ten researchers documented a significant decline in coral cover followed the two disturbances of 1991 (a major bleaching event and a cyclone), during which time they say that "coral cover (pooled among genera) declined from 51.0 9.5% in early 1991 to 24.2 14.4% in 1992, and 22.5 9.3% in 1993," which decline, as they describe it, was "among the most rapid of this magnitude recorded following natural disturbances." In contrast, however, they determined that "the bleaching events of 1994, 2002 and 2003 had no detectable effects on coral cover, even though the thermal anomalies causing these events and their short-term impacts in terms of bleaching prevalence were similar to the 1991 bleaching event."

What it means
Adjeroud et al. say their results reveal that "corals can recover rapidly following a dramatic decline," and they note that similar recoveries of coral cover have been documented at several other locations, citing the work of Connell (1997), Halford et al. (2004), Emslie et al. (2008) and Sheppard et al. (2008). In addition, they state that their work "supports the hypothesis that some reefs will undergo gradual changes in structure of their coral communities in response to major stress rather than collapse abruptly," citing the studies of Loya et al. (2001), Hughes et al. (2003) and Wakeford et al. (2008). Hence, there is significant real-world evidence that suggests that earth's corals may not be nearly so quick to succumb to the thermal stress of global warming as what the world's climate alarmists incessantly claim.

Connell, J.H. 1997. Disturbance and recovery of coral assemblages. Coral Reefs 16: S101-S113.

Emslie, M.J., Cheal, A.J., Sweatman, H. and Delean, S. 2008. Recovery from disturbance of coral and reef fish communities on the Great Barrier Reef, Australia. Marine Ecology Progress Series 371: 177-190.

Halford, A., Cheal, A.J., Ryan, D. and Williams, D.McB. 2004. Resilience to large-scale disturbance in coral and fish assemblages on the Great Barrier Reef. Ecology 85: 1892-1905.

Hughes, T.P., Baird, A.H., Bellwood, D.R., Card, M., Connolly, S.R., Folke, C., Grosberg, R., Hoegh-Guldberg, O., Jackson, J.B.C., Kleypas, J., Lough, J.M., Marshall, P., Nystrom, M., Palumbi, S.R., Pandolfi, J.M., Rosen, B. and Roughgarden, J. 2003. Climate change, human impacts, and the resilience of coral reefs. Science 301: 929-933.

Loya, Y., Sakai, K., Yamazato, K., Nakano, Y., Sambali, H. and van Woesik, R. 2001. Coral bleaching: the winners and the losers. Ecology Letters 4: 122-131.

Sheppard, C.R.C., Harris, A. and Sheppard, A.L.S. 2008. Archipelago-wide coral recovery patterns since 1998 in the Chagos Archipelago, central Indian Ocean. Marine Ecology Progress Series 362: 109-117.

Wakeford, M., Done, T.J. and Johnson, C.R. 2008. Decadal trends in a coral community and evidence of changed disturbance regime. Coral Reefs 27: 1-13.

Reviewed 25 November 2009