Coral mortality in Kenya affecting Astreopora, Montipora and Echinopora.

Mon Feb 25 01:28:28 EST 2002

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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