bleaching and erosion

[Billy Causey]

Dear Jacques,
Thank you for sharing these observations of coral bleaching.  For some time now
I have suspected and have been reporting at some meetings, that I have observed
a steady intensification of coral bleaching in the Florida Keys since 1980
(minor event) until the more recent 1997-98 back-to-back coral bleaching events
when our reefs remained in some degree of bleaching from July 1997 to the
winter of 1998.  While the bleaching was originally restricted to the outer
reefs (1983 and 1987).... coral bleaching began to occur in the shallow,
nearshore waters affecting the nearshore patch reefs and isolated coral
formations (1990, 1997, and 1998).  Soon, I hope we will have the water
temperature data compiled from 27 thermographs installed by Sanctuary
Biologists Harold Hudson and Bill Goodwin throughout the FKNMS that will show
the pattern.  However, at this time I suspect we have seen the inshore coral
that had historically acclimated to a broader range of physical parameters
(i.e. water temperature) now being pushed to the upper limit or threshold of
their tolerance to warm or hot water temperatures.

Whereas, during the earlier bleaching episodes (1980, 83, and 87) ... the outer
reefs, which had previously existed in a more narrower range of physical
conditions were first pushed to their upper threshold of tolerance.

But let me stress, I am by no means promoting temperature as the sole causative
factor of bleaching.
So .... I suggest you watch the corals in the lagoon and see if they bleach in
future episodes.

Cheers, Billy

Jacques Laborel wrote:

> Dear coral listers
> I  follow with great interest the debate upon coral bleaching.
>  Last october I could survey  Gaidoo atoll, one of the innumerable "virgin"
> maldivian atolls that was more or less completely destroyed by the 1998
> event. Like Bernard Thomassin and others I found  that bleaching had been
> more severe on the outer ocean facing subvertical slope of the reef (about
> 100% from surface down to about 35 metres deep) than in the lagoon. In fact
> the less affected zone we observed was a wide patch reef  between 3 and 15
> m deep in the shallower part of the lagoon with "only" 50 to 60%
> destruction. This was the only place on that atoll where Mussids and some
> Faviids were still alive.
> In fact the place were young colonies were more abundant were small reefs
> near the city-island of Malé, and subject to pollution and man
> disturbance...In Gaidoo, however,  all branching species had beeen wiped
> out. More resistant genus were Goniopora and Diploastrea.
> This is already  well known. But there is something that stunned me :  it
> was the absence of sea urchins, either out on the reef or hiding in coral
> thickets: during our three week stay  I saw exactly 3 Diadema !.
> I had already surveyed sea-urchin depleted reefs in the carribean during
> the big Diadema disease of 1984-85 and had been struck by the immediate
> development of brown algae, Sargassum, Turbinaria and the like, immediately
> capping coral colonies; but here, there were NO macrophytes at all (the
> only Caulerpas  found were on sand). Filamentous algae were  abundant on
> dead coral inside the lagoon but the outer slope was a white graveyard of
> coral colonies, gouged  and abraded by  what seemed to be parrotfish action.
> Some branches of Acropora palifera had lost about 6 cm in two years (raw
> evaluation) and appeared pure white except for a small development of
> Corallines on their base. This seemed to me a perfect example of
> overgrazing. Unfortunately no night dives were possible. I am afraid fish
> fauna is beginning to suffer from the disappearing of corals.
> Best wishes to all
>
> Jacques Laborel
> La Ciotat France
>
> Jacques & Francoise Laborel
> Chemin des grands Bassins,13600 La Ciotat, France
> tel. (33) 04 42 83 60 32
> fax. (33) 04 42 71 81 68
> e-mail : rutabaga at pacwan.fr
> visitez nous sur
> http://www.jardinesperance.org
>
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--
Billy D. Causey, Superintendent
Florida Keys National Marine Sanctuary
PO Box 500368
Marathon, FL 33050
(305) 743-2437 phone
(305) 743-2357 Fax
billy.causey at noaa.gov
http://www.fknms.nos.noaa.gov/


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For directions on subscribing and unsubscribing to coral-list or the
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