[Coral-List] Porites Line Disease - Red Sea Photos: Rates of spread, progressive necrosis, and algae colonization

[Thomas Goreau]

Doug Fenner's points below are well taken, but I think not correct in  
this case. He is quite right that progressive necrosis is the test of  
a disease, and this requires time series observations. In addition,  
as he is points out, the growing edge of a Porites overgrowing an old  
dead area can also show a pale rim of about the same thickness as  
PLD. But this is different from PLD in two subtle regards that  
require very close observation. Regrowth areas don't show the fuzzy  
necrotic looking tissue and short mucus strands that PLD does, and  
the regrowth areas are distinctively elevated at the growing edge  
above the dead coral it is overgrowing, whereas PLD shows a flat  
surface. If you look closely at Zaki's photographs you can see  
examples of both.

The point about the color gradation of the algae overgrowing recently  
dead coral tissue is also correct, but this is extremely dependent on  
the rate of tissue die back. It is very visible in the case of White  
Plague/Syndrome because this disease is the fastest spreading disease  
of all, of the order of centimeters per day, and it takes days for  
algae to overgrow dead skeleton in most places, depending on the  
nutrients. However most other coral diseases kill tissue at at least  
an order of magnitude slower rates, typically only centimeters per  
month or less, and in this case the overgrowing algae are able to  
keep up with the die back and the pale recently dead skeleton band   
is not visible. You can also sometimes see a narrow algae-free pale  
band in the fastest spreading cases of Black Band Disease but not in  
the slower ones.  It is very rare to see this pattern in Yellow Band  
Disease or Dark Spot Disease. I have seen it in PLD but it is fairly  
rare.

We urge interested coral researchers making regular long term  
observations in the field to closely follow the progress of this  
phenomenon over time. I believe that Dean Jacobson in Majuro has been  
taking time series photos to track the rate of spread since sometime  
last year, when I showed him film of PLD in Majuro from 1997.

Thomas J. Goreau, PhD
President
Global Coral Reef Alliance
37 Pleasant Street, Cambridge MA 02139
617-864-4226
goreau at bestweb.net
http://www.globalcoral.org

On Jan 12, 2008, at 7:23 PM, Douglas Fenner wrote:

> Zaki,
>    I just looked at your photos.  I see dead areas, I see a thin  
> white edge on the living coral in some photos, but I don't see  
> signs of active disease that kills coral.  Active disease that  
> kills coral moves across the coral at some speed.  Thus, the dead  
> area near the edge of the living coral has been killed more  
> recently than dead areas farther from the edge of the living  
> coral.  Turf algae colonize dead surfaces over a period of days to  
> weeks after it is killed.  As a result, when you see a disease like  
> white syndrome, you see a white dead area near the edge of the  
> living coral which grades into a light green then a dark green then  
> perhaps a nearly black area, which reflects the increasing growth  
> of the turf algae with time after a particular area of coral was  
> killed.  In your photos, the dead areas do not show this kind of  
> zonation.  In most of them the dead areas have uniform heavy turf  
> filled with sediment.  The dead area was killed quite a while  
> before the photo, and there is no active disease at the edge of the  
> living coral.  The white line then is most likely some kind of  
> irritation, as are pink edges.  Something definately killed that  
> dead area, but it happened long ago enough that it will likely not  
> be possible to determine what killed it, and there is no currently  
> active disease.  At least one of your photos shows an area killed  
> much more recently, but again there is no color gradient and no  
> evidence of active disease moving across the coral. Something  
> certainly killed it, I don't know what.  I suppose you can call  
> anything that kills a disease (state of ill health), including fish  
> bites, but I see no evidence of an infective microbial disease  
> killing coral at the time of the photo.  I'll let Laurie comment on  
> the white spots.   -Doug
>
> ----- Original Message ----- From: "Zaki Moustafa"  
> <zakimou at comcast.net>
> To: <Coral-List at coral.aoml.noaa.gov>
> Cc: <goreau at bestweb.net>
> Sent: Friday, January 11, 2008 4:55 AM
> Subject: Re: [Coral-List] Porites Line Disease - Red Sea Photos
>
>
>> Dear Coral-Listers,
>>
>> I just got around to posting some of my coral disease photos taken  
>> from
>> a fringing reef in the Gulf of Suez.  With the generous assistance of
>> Dr. Goreau, I was able to identify and subset some examples of what
>> we are referring to as Porites Line Disease.  The last two photos  
>> showing
>> white pox marks may be the Porites Ulcerative White Spot Disease
>> Laurie Raymundo mentions.
>>
>> Photos are posted at the following link:
>>
>> http://i258.photobucket.com/albums/hh263/zakimou/Red%20Sea%20Gulf% 
>> 20of%20Suez%20PLD
>>
>> Regards,
>> Zaki Moustafa
>>
>>
>