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Porites Line Disease

 Tom Goreau, President, Global Coral Reef Alliance

November 22 2007

Far and away the most common disease syndrome in the Indo-Pacific is what I call Porites Line Disease, which has many forms and is very widespread and abundant, affecting primarily massive Porites, but also branching species. The white or grey lines are by far the most common, followed by brown, pink, and blue. I first noticed this disease in the Marshall Islands in 1997, and since then have noticed it on every single dive in the Pacific and Indian Oceans. I have pointed it out to local researchers almost everywhere, only a few of whom had noticed it. I have not had the time, money, hardware, or software to grab or tabulate the thousands of video images I have taken of it all across the Indo-Pacific, or formally described it in a paper. Although I am not aware of any publications on this syndrome, I know that several researchers have followed its progress at specific sites, and may have published descriptions, but I am not sure what they have called it.

PLD is distinguished by a narrow line of necrotic tissue, usually around a millimeter wide, which separates live from dead tissue. The color of the line can vary between white, grey, brown, pink, blue, or purple. The disease advances on the order of centimeters per month or more, as can be seen in the fact that in many cases, the height of the living tissue (which grows upward at around one centimeter per year is not much higher than the dead surface). The pink line variant was independently discovered and has been described in published papers in India as Pink Line Disease by Ravindran and the Raghukumars who isolated a fungus from samples in Lakshadweep (where it was the most common variant, and where I looked at with Ravindran in 1998), but they did not look at other color variants, and it is not clear if the fungi is a primary pathogen or a secondary opportunist. Because I work with no funding I have never been able to take microbiological samples for genetic sequence analysis, so I do not know if each of these many different color lines are different manifestations of the same basic disease, or if each is associated with different pathogens. Much microbiological work is clearly needed.

 What is especially alarming about this disease is that although it is much slower and affects many less species than White Plague (or what some call White Syndrome when they can't find Aurantimonas coralicida), it is progressively killing the species that are the major survivors of all habitats that have been severely stressed, whether by bleaching or sedimentation. People should be aware of this and look out for it.

Thomas J. Goreau, PhD