What was done
The authors review what is known about the responses of real-world coral reefs to high-temperature-induced bleaching, focusing primarily on the Arabian Gulf, which they say "has recently experienced high-frequency recurrences of temperature-related bleaching (1996, 1998, 2002)."

What was learned
Riegl reports, first of all, that in each of the three high-temperature years, sea surface temperature (SST) anomalies of 2 to 2.5°C above average in situ measured summer maximum SSTs persisted from April to September, and that local maxima of in situ measured SSTs were 35.5°C in 1996 and 37°C in 2002. In response to these high-temperature events, they say that Acropora, which during the 1996 and 1998 events always bleached first and suffered heaviest mortality, bleached less than all other corals in 2002 at Sir Abu Nuair (an offshore island of the United Arab Emirates) and actually recovered along the coast of Dubai between Jebel Ali and Ras Hasyan.

What it means
Riegl states that "the unexpected resistance of Sir Abu Nuair Acropora to bleaching in 2002 might indicate support for the hypothesis of Baker (2001) and Baker et al. (2002) that the symbiont communities on recovering reefs of the future might indeed be more resistant to subsequent bleaching," and that "the Arabian Gulf perhaps provides us with some aspects which might be described as a 'glimpse into the future,' with ... hopes for at least some level of coral/zooxanthellae adaptation." We agree, and note that you can find more encouraging information on the symbiont shuffling hypothesis under Coral Reefs (Bleaching - Responses: Symbiont Shuffling) in our Subject Index.

References
Baker, A.C. 2001. Reef corals bleach to survive change. Nature 411: 765-766.

Baker, A.C., Starger, C.J., McClanahan, T.R. and Glynn, P.W. 2002. Symbiont communities in reef corals following the 1997-98 El Niño - will recovering reefs be more resistant to a subsequent bleaching event? Proceedings of the International Society of Reef Studies (Abstract Volume 10: European Meeting, Cambridge, UK, September).