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Intriguing realities of coral reef degradation and the new baselines for conservation

Posted by NiyazAhmed on 17 Mar 2008 at 17:23 GMT

Imagine a medical microbiologist mutating into a coral-reef ecologist! This came true when I was recently handling these interlinked manuscripts at PLoS ONE (1, 2) and following an extremely exhaustive and rigorous peer-review!, more so than I have ever seen, I myself became deeply interested in the field of coral reef ecology!

It is now two weeks since these articles were published and an overwhelming interest of the community is already evident from many evaluations and blog posts apart from wide media coverage that these articles have elicited. Beyond this, I thought an 'outsider's perspective' on the 'PLoS coral reef package' is really needed. I am sure such a perspective as this (see below) will catalyze start of a discussion involving also the non-experts apart from the coral community members.

In the current scenario of colossal public attention to environmental problems and far-reaching consequences of related studies published in open-access journals, the science of coral reef ecology seems to have stratified into two major paradigms: A) coral reef degradation is the outcome of direct human impacts such as overfishing and development and conservation efforts therefore, should focus on these aspects and B) decline of corals is largely the result of global climate change and microbial 'pathogens' and conservation resources should focus on these issues. Obviously these are the two extremes which need to be balanced. The ‘PLoS coral-reef package’ [comprising of the paper of Sandin and colleagues (1) published together with another article in PLoS ONE (2) and an essay at PLoS Biology (3)] indeed denotes that the much-needed balancing act has just started.

The authors convey (1, 3) that coral reefs in remote areas with less human inhabitation support thriving of more fishes and commonly have healthier and bountiful corals than reefs in more populated areas. They suggest that local protection of reef trophic structure may be critical in their conservation (1). However, they also warn of the poor understanding that prevails about the natural reef trophic structure and community organization. Moreover, because the present day reefs are so deranged and altered, studying them to understand natural reef function may be like studying cattle ranches in the tropics to understand function of the tropical forests that were long replaced by the ranches.

Having said that, the authors stressed on the need for an understanding of how local bio-geo-climatic impacts in synergy with global change affect the structure, function, and resilience of a coral reef. Sandin et al in their paper (1) document the ecology of perhaps the most pristine reefs that exist, and highlight the gradient of various impacts occurring across the chain of islands with increasing human inhabitation. However, it appears that they chose to focus heavily on an interpretation in which fishing and development cause the decline in coral and altered fish community structure. Although the essay of Knowlton and Jackson (3) did not elaborate microbial causes of coral degradation, the issue was addressed separately (2) through metagenomics that revealed linkages between human inhabitation/activity and the incidence of unhealthy corals. The observed increase in the abundance of microbes in water columns studied, and assignment of such microbes to potential pathogenic groups as shown (2) are the indicators of a very real potential for coral reef degradation. The data generated in the form of metagenomes and viromes from sea microbial communities are in fact an invaluable resource.

While it is satisfying that praises of these papers clearly outweigh the objections, there exist notable criticisms of the interpretations made out of correlative studies rather than experimental. But thanks to this fact that correlational studies are often the only option when trying to collate bio-geo-climatic patterns. Another criticism could be made of the choice to refer to sets of organisms as 'opportunistic pathogens'; it should not be taken to mean that these organisms are classical pathogens themselves. For example, saprophytic mycobacteria despite their having highly conserved genomic overlaps with major dreaded forms (M. tuberculosis and M. leprae), do not represent seasoned pathogens. The issue behind this difficulty is the rampant genomic fluidity expressing as phenotypic versatility of the microbial players. Finally, this 'coral-reef package' (1, 2, 3) is a big leap towards the general understanding of the biology and ecology of reef degradation and their prospective conservation. I believe these efforts (1, 2, 3), although not an ultimate decree on the coral reef ecology should nonetheless serve as an important foundation for future studies.

1) Sandin SA, Smith JE, Demartini EE, Dinsdale EA, Donner SD, Friedlander AM, Konotchick T, Malay M, Maragos JE, Obura D, Pantos O, Paulay G, Richie M, Rohwer F, Schroeder RE, Walsh S, Jackson JB, Knowlton N, Sala E (2008). Baselines and degradation of coral reefs in the northern line islands. PLoS ONE 3:e1548.

2) Dinsdale EA, Pantos O, Smriga S, Edwards RA, Angly F, Wegley L, Hatay M, Hall D, Brown E, Haynes M, Krause L, Sala E, Sandin SA, Thurber RV, Willis BL, Azam F, Knowlton N, Rohwer F (2008). Microbial ecology of four coral atolls in the northern line islands. PLoS ONE 3:e1584.

3) Knowlton N, Jackson JBC (2008). Shifting Baselines, Local Impacts, and Global Change on Coral Reefs. PLoS Biology 6: e54.