bleaching and erosion
rutabaga at pacwan.fr
Thu May 17 06:12:57 EDT 2001
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
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
For directions on subscribing and unsubscribing to coral-list or the
digests, please visit www.coral.noaa.gov, click on Popular on the
menu bar, then click on Coral-List Listserver.
More information about the Coral-list-old