nutrient deficiency and bleaching -and- Perhaps you need to do a bit more reading ...

[Bernard THOMASSIN]

To: Debbie MacKenzie <<debimack at auracom.com>
From: Bernard THOMASSIN <<thomassi at com.univ-mrs.fr>
Subject: Re: nutrient deficiency and bleaching -and- Perhaps you need =20
to do a bit more reading ...

Dear Debbie and all colleagues interested by coral bleaching,

To the comment:

> How come that bleaching is usually more severe nearshore, where
> nutrients are enhanced to levels, which in turn can become detrimental
> to many coral reef organisms, which are highly adapted to exist in
> oligotrophic conditions? Could that maybe relate to some patchiness,
> too: too much 'food' and maybe toxic substances?

I don't agree with this opinion taking as example that occured around
Mayotte Island in the North of the Mozambique Channel, SW Indian Ocean,
where I studied since 1983 several bleachings of various intensity.

Here the huge bleaching event of the April-June 1998 (when an warmer
mass of oceanic seawater coming from the North reached this SW Indian
Oc. area) -the bleaching was undubfully caused by the seawater
temperature increase : T=B0 C reached up to 32=B0 C in ocean open sea and
stayed as during near 3 months, it was the corals from the outer slopes
of the barrier reefs (187 km long) that bleached  and then died, mainly
in the shallow depths (3m down to 15-20m  - but encrusting corals at
down 30m also bleached -) : all the tabular and branched Acroporids,
all the Pocillopora, some Diploastrea, some massive Porites (but on
some of them parts were kept alive, if most of the colonies died). Even
Sarcophyton and Sinularia bleached, as well as the large sea-anemones
as Heterotactis magnifica, and some Tridacnids. So, consequently, the
barrier reef slope coral communities were destroyed at more than 85
percent.

On the slopes of lagoonal reefs, as well as on the slope of the
fringing reefs, also the bleaching occured, but on the fringing reefs
in muddy environments of deep coastal bays, most of the corals
survived.

My opinion (exposed in one of our Bali's Conf. posters) is that corals
living in clear oceanic waters on the barrier reef slopes or lagoonal
reef slopes near large passages, live in oceanic seawaters showing more
constant parameters (according to the seawater temperature they are
more "stenothermes"). In contrary, corals living in nearshore
environments where seawater parameters are more variable (increase of
temperature due to closed environments, or decrease of temperature due
to cool groundwater seepages ; salinity variations due to rainfalls and
river flows ; variation of the turbidity due to alluvial inputs
associated with rainfalls or to phytoplankton blooms ; bacterial
attacks from terrigeneous materials ; etc...).=20

In fact coastal populations of corals (for the same species) are more
resistant to all the possible stresses that coral populations living in
more stable and constant seawater conditions.

In this conditions I disagree with your opinion.

But be very carefull with the biology/physiology of corals. I begin to
believe that the same species of corals have not the same biology (and
physiology) in region located fare away. So extrapolations of results
from one area to another one are not possible. This is true for the
biologists and ecologists, but also for our paleo-geologist
colleagues.

This can explain the opposite views between different researchers!

Have a good day.

Sincerely yours.

Bernard

Bernard A. THOMASSIN
CNRS-UMR 6540 "Dimar",
Centre d'Oc=E9anologie de Marseille,
Station marine d'Endoume,
Chemin de la batterie des Lions,
13007 Marseille,
France

(33) 04 91 04 16 17 (ligne directe)
(33) 04 91 04 16 00 (standart)
mobile (33) 06 63 14 91 78
fax  (33) 04 91 04 16 35 (=E0 l'attention de....)

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