Thursday, September 14, 2006

El Nino on the way

There's a mild El Nino event brewing in the Pacific. The forecasters have suspected as much for the past couple months. The latest data (right) showing abnormally warm water in the central and eastern Equatorial Pacific led to the El Nino forecast by NOAA.

This is not expected to be anything like the strong 1998 El Nino event. But we will probably see some of the climate effects of El Nino, including dry weather in Australia and the western Pacific, a milder winter and spring in central North America and wet weather in Florida and the Gulf Coast.

The warming in the central Pacific could impact the reefs there. The coral bleaching event I surveyed in western Kiribati (intersection of the equator and the dateline, right under the orange spot in above map) in 2004 occurred after a very similar build-up of ocean temperatures from July-December. Bleaching is a paling caused by a breakdown of the symbiosis between the coral, the reef-building animal, and the colourful algae that lives in the coral's tissue. If the conditions that cause bleaching persist, like abnormally ocean waters, the corals can die. That's not the end of the story, though. The reefs can recover - the evidence from my colleagues suggests the corals have been returning after the high mortality we measured. The ecological questions are more how the community changes due to a bleaching event, and what happens if the disturbances (ie. the warm water) occur more frequently than in the past.

A couple weeks ago, NOAA Coral Reef Watch put out a bleaching warning for western Kiribati and the U.S. islands in the area (thanks in small part to my ranting). It will be interested to see, if the temperature stress continues to build, how the coral community responds. There is evidence that some corals can acclimate or adapt to warming ocean temperatures, by shifting the symbiosis to more temperature-tolerant algae. This may be an interesting test. Now if only someone wants to fund my research proposal...


teresa said...

what is the significance of putting out a bleaching warning? (this is not a warning like: "do not look directly at bleached coral! the glare off their striking whiteness is likely to cause corneal damage!") does that mean if fishermen/other locals see bleached corals they write it down and call someone or what?

Simon Donner said...

The warnings generally serve two purposes.

First, like you mentioned, a warning helps the scientific community coordinate data collection. Last year, the warning system helped NOAA Coral Reef Watch gather a mountain of field data from the Caribbean about extent of bleaching, species affected, etc. It is now being contrasted with the satellite-derived temperature indices to improve our understanding of the relationship between the heat stress and mortality in the Caribbean.

Second, it may be uesful in management. While a marine park manager can’t dump some magic potion on the reef to inoculate the corals from stress, reducing other pressures (recreational divers, fishing, etc.) may enhance the ability of the ecosystem to recover from whatever bleaching that occurs.