Are Bleached Corals Dying, Or Restocking Their Pantries?
July 12, 2004
Woeful cries have arisen from the environmental community over bleaching coral reefs around the world. The eco-activists say they’re dying, due to global warming and higher sea temperatures. And it’s true that corals bleach when the water temperature goes up.
A Greenpeace website says, “Corals will inevitably be among the first organisms to show the consequences of a sustained increase in sea surface temperatures, because of the fragile temperature dependence of the tiny algae, called zooxanthellae, which live in the coral’s cells. The coral’s color and most of its food come from these algae, so without them the coral cannot grow.”
The author of the World Atlas of Coral Reefs, Mark Spalding, claimed that a sudden rise in Indian Ocean water temperatures over a few weeks in 1998 destroyed 80 to 90 percent of that ocean’s coral. “Whole reefs around the Maldives and Seychelles pretty much died,” he said.
Scientists have been puzzled, however, by the fact that corals have survived more than 200 million years, even though they’re unable to move about and unable to protect their algae as the world has gone through warmer and colder periods. The Ice Ages must have dropped sea temperature considerably, and the Climate Optimum of 5,000 to 8,000 years ago was much warmer than today.
A coral core, drilled from a Pacific reef that dates back to 1726, shows the coral survived sea-surface temperatures 1.5 degrees Celsius higher than present in the mid-1700s.
That’s more than the Earth’s temperature has risen in the last 100 years, during a warming often declared “unprecedented.”
Experiments seemed to complicate the puzzle: not only do corals bleach when temperatures go up suddenly - they bleach when temperatures go down!
That was the clue, however. Bleaching is a coral’s system for dealing with temperature changes. The corals kick out the algae they’ve been living with that aren’t adapted to the new temperature, and pick up new partners.
Cynthia Lewis and Mary Alice Coffroth of the State University of New York/Buffalo, did an experiment that was recently reported in Science (June 4, 2004). They bleached some coral colonies, which ejected 99 percent of their symbiotic algae friends. They also exposed the bleached coral to a rare variety of algae that wasn’t in the coral colonies at the beginning of the experiment. Sure enough, within a few weeks, the corals had substantially restocked their algae shelves, and about half included the new algae. Later, the marker variety was displaced from several of the coral colonies by stronger algae strains - indicating that the corals pick the best partners for the new conditions from the whole variety of algae floating in their part of the ocean.
Ms. Lewis and Ms. Coffroth say this is a healthy demonstration of resilience and flexibility in coral colonies. Bleaching is a sign of stress, and some corals may actually die as a result of the stress. However, they say the coral systems have the flexibility to establish new associations with symbionts from the whole environmental pool . . .”a mechanism for resilience in the face of environmental change.”
That’s good, since the evidence of a natural, 1500-year solar-driven climate cycle has now been found in ice cores, seabed sediments, tree rings, cave stalagmites and pollen distributions worldwide. These cycles have been occurring for at least a million years. If the corals couldn’t adjust to such temperature changes-a roughly 4 degrees C-they’d have long since gone extinct.
Even the bleaching event in 1997-98, which the woe-sayers claimed had killed most of the coral in the Indian Ocean, was natural - the Pacific Decadal Oscillation, a temperature bump which occurs every 20-30 years.
The eco-activists and biologists who claimed man was killing the coral are wrong - again - as they were with claims that pesticides are deforming frogs. The frogs are deformed by a natural parasite, the trematode. They were wrong in claiming irrigated farming suppressed salmon numbers in the Pacific Northwest. The salmon numbers are controlled by the same Pacific Decadal Oscillation, every 25 years, that stresses the coral.
The woe-believers forget that Nature herself is harsh, stressful, and eternally competitive.
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