Recovery from bleaching: best thing to do is leave the reef alone

Scientists studied an untouched reef that suffered more than 90% loss during a bleaching event due to warming in 1998. They found that it was "almost restored to pre-1998 values at most shallow sites".

The findings indicate corals are much better equipped to successfully rebound from warming induced coral bleaching events when they are not impact by humans.

The authors conclude: "If we want to preserve earth's corals in the face of possible further global warming -- about which we can really do nothing -- our focus should be on trying to reduce the many deleterious local effects of humanity on coral reef environments, about which we can do something ... but only if we really put our minds, mouths and money to it".

Central Indian Ocean Coral Recovery from 1998 Bleaching
CO2 Science 1 Oct 08;

Reference
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.

Background
The "very remote" Chagos Archipelago spans an area of about 400 x 250 km in the central Indian Ocean and "mostly lacks reef fishing, shoreline construction, sediment disturbance, or local pollution," in the words of the authors, "which therefore do not confound recovery from the warming-induced mortality" that followed the 1998 bleaching event there, where "cover values of coral and soft coral on seaward slopes before 1998 totaled 50 to 95%, which declined in 1998 to an average of 12%, and even to zero between 0 and 5 m depth in some shallow areas."

What was done
Sheppard et al. measured the degree of coral recovery on seaward slopes of all five islanded atolls of the Chagos Archipelago from February to March of 2006.

What was learned
The three UK scientists report that "following very heavy coral mortality (mostly >90%) caused by the 1998 warming event, and despite two further sub-lethal bleaching events, the recovery of coral cover, colony numbers and juvenile recruitment has been good in many parts of the archipelago." In fact, they state that "in 2006, coral cover was almost restored to pre-1998 values at most shallow sites." Also, they report that "no shift was observed towards algal domination, or to assemblages dominated by Porites or faviids, as has been reported elsewhere."

What it means
Sheppard et al. write that "given that examples of reefs without local impacts are rare, these results illustrate the importance of reference sites such as this that lack local, direct effects," and as we have long contended, Sheppard et al.'s findings indicate that earth's corals are much better equipped to successfully rebound from thermal-induced coral bleaching events when they are not exposed to the direct deleterious localized effects of humanity, which make it much more difficult for corals to successfully recover from periodic exposure to dangerously high temperatures. Hence, it would seem to us that if we want to preserve earth's corals in the face of possible further global warming -- about which we can really do nothing -- our focus should be on trying to reduce the many deleterious local effects of humanity on coral reef environments, about which we can do something ... but only if we really put our minds, mouths and money to it.

Links to more recent articles about factors affecting the health of our seas

• Ocean "Dead Zones" Spread, Fish More at Risk - Study
  Alister Doyle, PlanetArk 1 Oct 08
• Pollution Slowly Killing World's Coral Reefs
  Jason Lange, PlanetArk 1 Oct 08;