Monday, September 20, 2010

The second "global" coral bleaching event

The NY Times has an article on the observations of coral bleaching across the planet over the past 12 months, an subject I've raised here in the past few months.

The NY Times article calls the concurrence of events "only the second known global bleaching of coral reefs". Though the characterization is awkward and not terribly accurate, as the bleaching is not really "global", it does point to the right comparison. The spatial extent of coral bleaching in 2010 is likely to be second to that observed in 1998, which people have taken to calling the first "global bleaching event". It is no coincidence that these "global" events occurred during two of the warmest, if not the two warmest, years in observed history.

It is also no coincidence that both 1998 and 2010 began with strong El Nino conditions, which later flipped to La Nina conditions. In a simplistic sense, that "maximizes" the area of ocean which experiences anomalous warmth that tends trigger mass coral bleaching events. This year, the El Nino event causes anomalous warmth in the eastern and central Equatorial Pacific. The migration of the West Pacific Warm Pool back westwards, as El Nino subsided, helped cause the high temperatures and bleaching in Southeast Asia and the Western Pacific. Atmospheric teleconnections may be responsible for some of the anomalous warmth in the Caribbean, as has been suggested in past studies. And as the article indicates, the recent switch to La Nina conditions is increasing concern about bleaching in the southwest Pacific, including the Great Barrier Reef, over the southern hemisphere summer.

One area of uncertainty in the science community is to what extent can coral reefs which have experienced bleaching in the recent past, whether 1998 or more recently, can become more resilient to future temperature stress. The year 2010 may serve as a great biophysical experiment.

[UPDATE: The Atlantic and Gulf Rapid Reef Assessment is inviting divers in the Caribbean to join them in "monitoring simple, ecosystem-
level pigmentation changes in live corals and any associated changes
in live coral cover using the newly updated BLAGGRA Line Transects
protocol ( Sites can be very quickly and
repeatedly surveyed by small teams of 1-2 experienced divers. A
representative assessment can be made of reefs in the area affected by
bleaching, and/or sampling can be focused on special-interest sites
(such as within and outside of MPAs)"]


Unknown said...

The other question is how often can events like this happen before before we start seeing serious and unrecoverable declines in coral reef ecosystems. That's the other part of this great biophysical experiment.

Simon Donner said...

True - two halves of the same question. We're examining this in the Central Pacific.