Friday, September 29, 2006

New discoveries, old myths?

There were more than a hundred presentations at the International Society of Reef Studies meeting in Bremen last week. I strung for New Scientist to help pay my way. The news editor asked for just one story, and preview of what will appear in next week's edition, albeit much cut, is posted directly below ( see "Algae kill coral by enhancing microbial activity").

The folks who wrote this paper recently took part in an expedition to the Line Islands, which harbour some of the remotest and most pristine coral reefs on earth. On Kingman reef, for example, sharks remain fantastically abundant at the top of a healthy food chain.

ISRS is a highly scientific meeting, but for many of those attending, I think, this is by no means incompatible with the capacity for sheer wonder. Two of the most distinguished speakers, John Pandolfi and Peter Mumby, clearly felt this. So while Pandolfi focussed on quite technical questions regarding the validity, or otherwise, of neutral and niche theories in ecology, he also spoke of the significance of "shifting baselines" -- the intergenerational amnesia that hides what is lost. Imagine, he said, the 17th Century Caribbean, its waters so full of turtles by one (apparently) reliable account that sailors could on occasion navigate at night by the noise of their thousands of shells clacking against each other. And although Mumby demonstrated a mathematical model for reef resilience his take home point was simply that we need to "spend more time in the water".

It hard from such a big meeting to single out particular stories for further comment. But among several that look to be important is the work on coral restoration by Buki Rinkevitch and others. Also of interest, and something on which further scrutiny may be welcome, is the observation by Andrew Baird that healthy ecosystems such a coastal forests and coral reefs did *not* reduce the damage to coastal communities of the December 2004 Indian Ocean tsunami (See Myth of the green belts, Samdura, No 44). Baird spoke fascinatingly too, but all too briefly, of traditional managements and conservation systems with a track record of more than 350 years in one area.

All this, and more, for further investigation in Coral Bones.


Blogger Caspar Henderson said...

An edited version of this article is likely to appear in the 6 October edition of New Scientist:

Algae kill coral by enhancing microbial activity
Caspar Henderson

Evidence for a previously unknown mechanism by which algae can harm coral reefs was presented at the meeting International Society of Reef Studies in Bremen, Germany last month.

“Our work shows that algae can indirectly cause coral mortality by enhancing microbial activity. The evidence indicates that it does this via the release of compounds likely to be dissolved organic carbon.” says Jennifer Smith a researcher at the National Center for Ecological Analysis and Synthesis at the University of California, Santa Barbara, and a lead author on the paper (Indirect effects of algae on coral: algae-mediated, microbe-induced coral mortality. Ecology Letters [2006] 9: 835-845).

The last several decades have seen an alarming decline in coral reefs around the world as a result of numerous factors including climate change, overfishing, eutrophication, coral disease. As corals die or become stressed they are generally replaced or out-competed by faster growing fleshy algae. These "phase-shifts" from coral to algal dominance result in a communities that are completely differnent in structure and function than the healthy coral-dominated state.. Perhaps the most poorly understood component of coral decline, say many scientists, is how coral disease, increasing algal cover, and human impacts such as pollution and overfishing, interact. Understanding these relationships is crucial for the development of conservation, restoration and management plans for coral reefs around the world, they say.

Smith and her colleagues performed a series of ship board experiments while on an expedition last summer to the Line Islands in the Central Pacific, some of the most remote and most pristine coral reefs left in the world. When coral and algae were placed in chambers together but separated by 0.02 micron filter that prevented the passage of microbes and viruses, corals suffered 100% mortality. With the addition of the broad-spectrum antibiotic ampicillin, mortality was completely prevented. Physiological measurements showed complementary patters of increasing coral stress with proximity to algae.

“You could make an analogy with gum disease in humans” says Stuart Sandin, a marine ecologist at University of California, San Diego and one of Smith’s co-authors, “with sugars fertilising bacteria already present on the coral’s surface, like those present in your mouth, so that these resident microbes multiply and become pathogens”.

Leading marine researchers have hailed the findings. “The [work] … is important because it highlights another potential mechanism by which macroalgal-dominated reefs could persist and reduce the likelihood of switching back to a coral-dominated state”, says Peter Mumby of the Marine Spatial Ecology Laboratory University. But he adds a caution. “The mechanism still needs to be examined under natural field conditions because laboratory-based studies may not adequately represent the effects of algae in nature”.

Smith and Sandin agree. “Our main goal was simply to show that there is a mechanism at work. Most ecologists study what you can see. But micro-organisms could be playing a major role at the foundations of reef ecology. The study opens up so many new questions that need to be addressed in the future”.

6:59 pm  

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