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

Esther Peters esther.peters at verizon.net
Sun Jan 13 20:29:12 EST 2008

   Thank  you very much for posting the photos.  Based on those images, I
   think  more  than  one  condition is present (fish bites and different
   diseases) and different stages in the disease processes.
   Photo  1 shows lesions typical of fish bites.  Photo 2 is labeled "PLD
   at  lower  left. The pink areas on top may be an inflammatory response
   around  recovering  parrotfsh  bites."   I  want to point out that you
   cannot identify an inflammatory response in a coral because the tissue
   is  "pink,"  it  is  going  to  require  histological  examinations to
   determine  whether  amoebocytes  have  increased in or infiltrated the
   tissue  and  why.   Discolored tissue (different color, paler, darker)
   suggests  that  cells  and tissues might be functioning abnormally for
   some  reason.  Disease  is  "any  impairment  to  an  organism's vital
   functions,  organs, or systems."  (And Doug, "progressive necrosis" is
   NOT  the test of a disease.)  Coral diseases are present which are not
   causing  rapid  tissue  loss,  as  Tom  notes below, and in some cases
   recovery  is  made  without  any  tissue  loss.   It  is  important to
   understand  why  the polyps' health is impaired, from whatever reason,
   and  histology  provides  a  means  to do so.  Early physiological and
   biochemical  functional changes can also be detected through the study
   of  biomarkers  before structural changes are evident with electron or
   light microscopy.
   Definitely,  disease  progress needs to be studied over time: grossly,
   microscopically,with  other  biomarkers,  and microbiological or other
   tools to fully understand the phenomenon.
   One  more  note  regarding  Porites  ulcerative  white  spot syndrome.
   Taylor  Reynolds  isolated a vibrio as the suspect agent, but when she
   exposed  coral  in  a tank to the cultured bacterium in the water, the
   whole  colony  was  killed.   Then  she  showed me a scanning electron
   micrograph  she  had happened to take, in which a single Porites polyp
   had  captured  and  half-swallowed  a  copepod  (its  tail  was  still
   protruding  from  the  polyp's  mouth).  I immediately thought of Rita
   Colwell's  group's  work  with Vibrio cholerae, in which the bacterium
   was  found  to  colonize  the  surface of copepods, which enhanced its
   survival  (Huq  et  al.,  Appl Environ Microbiol. 1983 January; 45(1):
   275-283).  If the copepod prey of Porites had the killer vibrio on it,
   that  might  explain  why single to small areas of polyps die, meaning
   mode of exposure to this bacterial pathogen is very important.  Longin
   Kaczmarsky  is  continuing  multidisciplinary  studies on this disease
   (and  notes  that  lesions  on  some  coral colonies may recover), but
   sometimes  a  chance observation from a different perspective provides
   more clues.
   The more perspectives on Porites line disease, the better!
   Esther Peters
   Thomas Goreau wrote:

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

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
Global Coral Reef Alliance
37 Pleasant Street, Cambridge MA 02139
[1]goreau at bestweb.net

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

   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"
[3]<zakimou at comcast.net>
To: [4]<Coral-List at coral.aoml.noaa.gov>
Cc: [5]<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
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
white pox marks may be the Porites Ulcerative White Spot Disease
Laurie Raymundo mentions.

Photos are posted at the following link:


Zaki Moustafa

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