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

[Thomas Goreau]

Dear Doug,

This is often a subtle phenomenon to be sure, there are many other  
things going on in Zaki's photos, and not all of these phenomena are  
linked to progressive mortality, close up time series observations  
are clearly needed, along with microbiology. In general though, low  
turf algae don't kill coral like some macrophytes do, they fill in  
the space after coral dies for other reasons. One can see many cases  
of dead patches on Porites completely overgrown by turf in which the  
boundary is stable, and indeed many where the coral is overgrowing  
the dead patches from the edges. I'm not counting those as PLD, only  
those cases where there seems to be a clear progressive retreat of  
tissue with a necrotic looking edge. Kaufman thinks all coral  
problems are caused by fish, but we are long familiar with fish bites  
and most of them heal with no necrosis at all.

Best wishes,
Tom

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 13, 2008, at 4:29 PM, Douglas Fenner wrote:

> Tom,
>     Thanks!  When I read your message, I thought, hey, that makes  
> sense.  OK, I'll buy that.  Then this morning I got to thinking,  
> hey, hang on a minute!  What you're saying is that the edge moves  
> at a rate that is below detection threshold for the color changes  
> that occur as turf colonize the skeleton.  White syndrome probably  
> moves around 20-30 cm per month.  We might be able to detect the  
> color changes on the newly dead skeleton if they were over about  
> 1mm wide.  1 mm a month is about 1/200 - 1/300th as fast as white  
> syndrome moves.  If the movement is so slow we can't see evidence  
> in the color of the newly dead skeleton, we actually don't have any  
> evidence it is moving.  Could be it is, could be it isn't.   
> Further, if it is moving very slowly, what's to say it's not moving  
> because the turf that is in competition with the coral aren't  
> winning the battle, and the white line is just from irritation as  
> the turf kills the coral??  OK, yellow band and dark spot may not  
> move fast enough to detect the color change as turf grows, but then  
> those diseases have large obvious color changes in the band that  
> demonstrate that something like disease is going on.  That's not  
> the case here.  It seems to me that the cause could be disease or  
> something else and I haven't heard strong enough evidence for  
> disease to convince a skeptic.  I don't know what causes these dead  
> areas and will try to keep an open mind until I hear evidence one  
> way or the other that is convincing.  Sounds to me like Les has a  
> lot of good ideas to explore.   -Doug
> ----- Original Message -----
> From: Thomas Goreau
> To: Coral-List at coral.aoml.noaa.gov
> Cc: Douglas Fenner ; Zaki Moustafa
> Sent: Saturday, January 12, 2008 2:02 PM
> Subject: Re: [Coral-List] Porites Line Disease - Red Sea Photos:  
> Rates of spread, progressive necrosis, and algae colonization
>
> 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
>>>