[Coral-List] causes of Acropora loss

Esther Peters esther.peters at verizon.net
Sat Oct 6 12:36:25 EDT 2007

   Diego, John, and "listers":
   I  wanted  to  add  a  correction  and word of caution to this thread.
   Diego, you noted
the WBD pathogen is a relatively common Vibrio species (most likely V. carchari
ae = V. harveyi), at least for A. cervicornis. We found differences  
(resistance?)among organisms, being some of them affected and dying much faster
 than others, in the presence of the same pathogen; moreover, disease  
stopped after couple days.

   and  this  is what has been found for white band disease type II, from
   analysis  of  coral surface mucopolysaccharide layer samples (Ritchie,
   Smith,  Gil-Agudelo).   But  histopathological  examinations  were not
   performed   on  those  affected  coral  colonies.  I  found  bacterial
   aggregates in A. cervicornis and A. palmata colonies affected by white
   band  disease  type  I, at Tague Bay, St. Croix (where Bill Gladfelter
   reported  the  first  observations  of  this  distinctive rapid tissue
   loss),  and  elsewhere  on  Caribbean  and  Florida  Keys reefs, using
   histological  techniques.   Both  of  these studies have shortcomings,
   because  the  "picture  of disease" is incomplete.  Current studies on
   "white acute unknown (WAX)" or "white subacute unknown (WSAX)" disease
   signs  on  these  species  and  their  hybrid (A. prolifera) are using
   histological,  microbiological,  and  molecular  techniques on samples
   collected  at  the same time or even on the same samples.  Based on my
   knowledge  of  these  studies  (I'm  not doing all this work, talented
   younger  colleagues  are,  too),  we  are going to have more surprises
   about these coral diseases.
   On  a  personal  note,  I remember talking with Bill Gladfelter at the
   West  Indies  Lab  when  I  was  starting  my  graduate studies and he
   wondered  if white band disease were not related to some environmental
   change.   After seeing Al Gore's graphs, the timing of when change was
   detected  (temperature related or something else) is certainly suspect
   for  contributing  to  the  elkhorn coral's demise there.  I estimated
   that  95%  of  the  elkhorn  off  Tague  Bay  had  died because of the
   epizootic  of  white  band disease by 1986, last time I was there.  In
   type  I,  tissue loss did not stop until the entire colony was gone (I
   think  only a couple of possibly resistant elkhorn colonies were found
   at  Tague  Bay). And the bacterial aggregates still might be a chronic
   or  latent  agent  that  could lead to tissue loss over time (based on
   Anderson, GG, JJ Palermo, JD Schilling, R Roth, J Heuser, SJ Hultgren,
   2003,  Intracellular  bacterial  biofilm-like  pods  in  urinary tract
   infections,  Science  301:105-107).  Note that James Duerden had found
   them  in  A.  cervicornis  from  Jamaica  in his 1902 work West Indian
   Madreporarian  Corals.  We need to keep our minds open to all sorts of
   And  that  includes  what  Diego is thinking about the acute, complete
   (100%)  massive  tissue  loss  of  thickets  of  A. cervicornis and A.
   palmata   off   the   Rosario  Islands,  as  being  the  result  of  a
   high-temperature-related  bleaching event in 2005.  He had seen the A.
   cervicornis  alive  3  months  before, and it appeared that the entire
   patches  had  died  (lost  tissue) within the same time period, on the
   order  of  a  couple  weeks  before.  John pointed out that white band
   disease  signs  were  not  associated  with  bleaching in the 1970s to
   1980s, and the linear tissue loss rate was on the order of mm per day,
   thus  entire  colony  mortality  could take a few months (on the large
   colonies that used to be seen on forereefs in the Caribbean).  So both
   mechanisms are quite plausible, as are others, potentially!
   Esther Peters
   John Bruno wrote:

Diego L. Gil-Agudelo, Ph.D. wrote:  Please, correct me if I?m  
wrong, but

diseases hardly affect 100% of the individuals of any population, as
supposedly happened with Acroporas in the 80?s

Hola Diego, You probably know a lot more that me about the etiology  
of white band disease.  And it is true that disease prevalence is  
often less than 100%.  But it can indeed be very high as it was for  
Acropora spp., Diadema, etc.   Outbreaks of infectious diseases that  
kill 95% or more of individuals are not that uncommon in marine  
systems.  There are many well documented examples of comparable  
urchin die offs all around the world, seagrass die offs (such as the  
epidemic that nearly extirpated seagrass in New England in the  
1930s), oyster diseases, etc. Kevin Lafferty has written a number of  
excellent reviews on this ([1]http://www.werc.usgs.gov/chis/
lafferty.asp).   And there are countless terrestrial examples; just
think of American Chestnut Blight ([2]http://www.apsnet.org/online/

(sorry, I was in high
school).  Besides, it is not good for pathogens to do so (who will
infect next?).

True, but many of these examples have resulted from the introduction
of novel pathogens; the pathogen and host have no evolutionary
history.   And of course pathogens, like all life forms, are not
optimized (otherwise they would have evolved wheels)-they do
sometimes wipe out their host (or nearly so-Ebola anyone) even though
this leads to their own demise.  We see predators do this all the
time too.  Just think of what an Acanthaster outbreak does to a coral

If our data is right (and I?m sure it is), the WBD pathogen
is a relatively common Vibrio species (most likely V. carchariae = V.
harveyi), at least for A. cervicornis.  We found differences
among organisms, being some of them affected and dying much faster
others, in the presence of the same pathogen; moreover, disease
after couple days.

That is interesting, but not surprising.  Remember you are working
with the 1% or so of the population (and their offspring) that
survived the epidemic.  The proportion of resistant individuals is
surely much higher now that it was 30 years ago before all the
susceptibles were weeded out of the population.

  This lead me to think that probably the Acropora loss
experimented during
the 1980?s was the product of bleaching due to thermal events.  I
know this
decade experienced strong Ni?o events, although I?m not aware of
showing the coincidence or not of these thermal events with reports on
Acropora die offs.

That is an interesting idea that was also discussed fairly
extensively in the recent paper in JEMBE by Lesser et al. (2007).
The trouble is, as far as we know, the early-mid 1980s (when nearly
all Caribbean coral loss seems to have occurred) was a relatively
cool period according to an analysis by Barton and Casey (2005); an
often overlooked and very important paper.  Additionally, the white
band symptoms were widely observed and documented-i.e., we saw it
happen and it was not bleaching, overgrowth by algae, sedimentation,
etc.  It was disease.

To my mind, this is the only kind of event we know that
can produce such massive deaths of these corals in such an ample
manner, in
a large geographic scale and in a short period of time.

See my comments above.   We do know that infectious diseases can
cause such rapid, devastating, and geographically widespread
population declines .  Did you see what happened to crows in the
eastern US in the early 2000s?  They and many other species suffered
rapid population declines due to West Nile Virus.


A GENRAL RANT, NOT DIRECTED TOWARD DIEGO:  Diseases are a common and
very important ecological phenomena.  Pathogens and parasites are at
least as important in regulating populations as competitors and
predators.  I think in some cases (not all) human alterations to the
environment have increased coral disease severity.   But we as coral
reef scientists don't need to continue to grasp at other explanations
for the Acropora die off of the 1980s.   White band disease was
clearly not bleaching, it was not caused by coastal development, by
nutrient pollution, by fishing or by algae.  It was/is caused by a
bacterial pathogen (as nicely shown in an excellent  paper by Diego
(Gil-Agudelo et al. 2006)) and its impacts were identical next to
large urban centers and on very isolated, unfished reefs.   We don't
need any convoluted explanations to understand what happened.

John B

Barton, A. D. and K. S. Casey (2005). "Climatological context for
large-scale coral bleaching." Coral Reefs 24: 536-554.

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