Coral mortality in Kenya affecting Astreopora, Montipora and Echinopora.

[Laurie Richardson]

What you describe sounds like the coral surfaces have become anaerobic.  The
"white dust" is probably a population of sulfide-oxidizing bacteria (look at
a sample under the microscope - if you see filaments full of bright granules
- stored elemental sulfur - then you are seeing the sulfide-oxidizing
bacterium Beggiatoa, which looks to the eye like white granules.  As to the
cause of death - it is unclear, just by visual observations, whether
something killed the coral and then an anaerobic bacterial population
developed, or if some imbalance occurred and massive oxygen consumption by
rapidly growing bacteria resulted in development of anaerobic
microenvironments which selected for sulfate-reducers which then produced
sulfide which then enriched for sulfide-oxidizers, etc.  The black layer is
probably precipited ironsulfide oxides.  Good luck!

CRCP wrote:

> Coral mortality in Kenya affecting Astreopora, Montipora and Echinopora.
>
> A new source of coral mortality has been observed in Kenya and is
> largely affecting Astreopora, Montipora and Echinopora but also
> Acropora, Platygyra and massive Porites.  Below is a description of the
> mortality and a request for others to make observations on these taxa
> and to assist identifying the source of the mortality.  This is not a
> localized source of mortality but is occurring on a scale of several
> hundred kilometers and has largely eliminated Astreopora and Montipora
> on Kenyan reefs.
>
> Observations made during the past two weeks indicate mortality
> significantly different from bleaching or local sources of mortality.
> In the early stages corals develop an ashy dull coloration with a
> brittle or weak skeleton while in the intermediate stages they become
> covered with mucus that collects debris.  Once the mucus and debris
> clears a white calcareous dust is left on the surface and sometimes an
> anaerobic blackness underneath, probably due to anaerobic microbial
> decay of the tissue under the mucus.  Death is very quick in less than
> two weeks. This description is particularly true for Montipora and
> Echinopora but Astreopora largely develops a dull pale color and then
> leaves a bare white skeleton, seldom producing mucus.  Echinopora is
> more variable, with patches of dead skeleton among living patches.
> Massive Porites turns from brown to ashy gray, becomes covered with
> mucus, but so far there has been few observations of mortality.
>
> Morbidity is not nearly as obvious as coral bleaching as the corals
> become dull rather than bright white and they are often hidden by mucus
> and a white dust as they die.  Also it is only affecting some taxa and
> there has been no coloration change in other taxa, not even a paling.
> Also, bleaching for these massive species is often protracted taking
> weeks to months to die and the colors are more vibrant.  During the
> recently observed mortality, death is rapid and the colors are dull and
> do not attract attention.  Astreopora is fairly resistant to bleaching
> and in this case it is the worst affected.  Unlike commonly reported
> microbial diseases that form bands, there is no band formation, just an
> ashy or loss of color, mucus and death beneath the mucus.  This was only
> recognized from other sources of mortality because of continuous
> fieldwork in different sites and might have otherwise been attributed to
> local factors and mortality.
>
> Because observations of this death in northern Kenyan corresponded with
> a red tide, there was a possibility that this caused the death.  This
> may not be the case, however, as there were no red tides in southern
> Kenya.  There was a 3-4 day bloom or current drift of gelatinous
> zooplankton in southern Kenya, but it was not associated with rich
> plankton.  The weather has been windy, but not terribly strong and the
> water is cool for this warm season at about 28oC in southern Kenya and
> as low as 26oC in northern Kenya.  It is possible that this is caused by
> water chemistry changes, but the taxa-specific response is very curious.
>
> I have a few specimens that were in the final stages of death preserved
> in Formalin, Alcohol and DMSO solution.  If somebody would like to try
> to figure the cause of death I will send samples of this tissue.  If
> somebody knows somebody competent to do this analysis, please pass on
> this email to him or her.
>
> I suggest that others in the field keep an eye out for this phenomenon,
> it is not as obvious as coral bleaching but if one begins to look for
> these taxa they will notice that all of the individuals that they see
> have either recently died or are about to die.  It occurs very fast and
> turf algae quickly colonize the skeletons, so one needs to be vigilant.
>
> I will only be at this address until Friday the 1st of March and can
> then be contacted at tmcclanahan at wcs.org or call me in the US at WCS
> Marine Programs 718-220-5885 after March 7th.  I will bring coral tissue
> with me in case somebody in the US would like to examine it.
>
> Tim McClanahan  crcp at africaonline.co.ke
>
> Julie Church  juliec at africaonline.co.ke
>
> --
> Tim McClanahan
> Coral Reef Conservation Project
> The Wildlife Conservation Society
> Kibaki Flats #12
> Kenyatta Beach, Bamburi
> P.O. Box 99470
> Mombasa, Kenya
> email: crcp at africaonline.co.ke
> Tel O: 254 11 485570
> Tel H: 486549
>
> ~~~~~~~
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--
Laurie L. Richardson
Associate Professor
Department of Biological Sciences
Florida International University
Miami, Florida  USA   33199

phone:  305/348-1988
fax:  305/348-1986
email: richardl at fiu.edu

~~~~~~~
For directions on subscribing and unsubscribing to coral-list or the
digests, please visit http://www.coral.noaa.gov, click on Popular on the
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