Nearshore vs. offshore bleaching

Ove Hoegh-Guldberg oveh at uq.edu.au
Sun May 20 18:46:47 EDT 2001


Bob B and co are probably correct in saying that "both 'corals' and their
microenvironments exhibit systematic differences over rather small scales."  I
suspect that we differ in how certain we would be of the causes of these
differences (real?, genetic?, phenotypic?).  There are many observations that
would also seemingly contrast conclusions that inshore, presumably more stressed
corals bleach less (e.g. HG and Salvat 1995, Berkelmann and Oliver 1999 - just
two off the cuff cases in which inshore sites were more than often more bleached
in 1998 etc. ... from the literature too!)

As many have been indicating, much is speculative and little is locked down at
this point.  I still feel that we have to be very careful in distinguishing
between good, untested ideas (that should be tested) and ideas that have been
verified by solid experimental methods and field observations etc.  The former
category (no criticism intended) would characterise much of our discussion so
far.  The latter category has few lines to it.

Ove

-----Original Message-----
From: owner-coral-list at coral.aoml.noaa.gov
[mailto:owner-coral-list at coral.aoml.noaa.gov]On Behalf Of Billy Causey
Sent: Sunday, 20 May 2001 5:52 AM
To: Bob Buddemeier; coral list
Subject: Re: Nearshore vs. offshore bleaching


Bob,
I wish I had seen your excellent response before I sent mine yesterday.
Unfortunately I am making my way down a list of hundreds of back-logged messages
and
just came to your comments.  Excellent!  Billy

Bob Buddemeier wrote:

> On the basis of evidence available at the time we (Buddemeier, R. W. and
Fautin,
> D. G., 1993, Coral Bleaching as an Adaptive Mechanism, Bioscience 43:320-326)
> observed that:
> "There are consistent habitat differences in bleaching resistance at a given
> locale; corals in habitats that are more variable or more prone to stresses of
> various sorts, including thermal (such as shallow water or fringing reefs),
tend
> to be less bleached than those in more normally equable environments."
>
> Apparently the field observational patterns are more consistent than attention
to
> the literature.
>
> The reasons can be described as aclimatization, adaptation, or different
> 'ecospecies' occupying the different habitat niches, but they all boil down to
the
> fact that both 'corals' and their microenvironments exhibit systematic
differences
> over rather small scales.
>
> Bob Buddemeier
>
> John Naughton wrote:
>
> > To add to the mix, I concur with Bruce's statements below. During the recent
> > severe bleaching event in Palau, we noted that corals in the lagoon close to
> > the main island of Babeldaob were basically not impacted, while much of the
> > coral (particularly Acropora) on the barrier reef was hammered.  Could this
be
> > attributed to the possible lowering of nearshore water temps from runoff?
> >
> > Mahalo,  John
> >
> > John Naughton
> > NMFS, Pacific Islands Area Office
> > Honolulu, HI
> >
> > Bruce Carlson wrote:
> >
> > > RE: Offshore vs nearshore bleaching
> > >
> > > Bernard Thomassin disagreed with the general statement that bleaching is
> > > usually more severe nearshore.   I concur.
> > >
> > > The other day, Gregor posted a message that "The pattern of bleaching
> > > follows a consistent trend globally that suggests that following bleaching
> > > events, reefs located in areas with less water column mixing are usually
> > > the worst affected. Typically these are inshore reefs where both nutrient
> > > flux and absolute levels of nutrients are likely higher than outer reefs."
> > >
> > > I wrote to Gregor saying that my data indicate that both nearshore and
> > > offshore reefs in Fiji (south of Viti Levu) suffered significant bleaching
> > > last year.  When I revisited my transects this year I found that both
areas
> > > suffered high mortality (>95% Acropora dead), but I also found significant
> > > regrowth ("phoenix" corals) and significant recruitment in the lagoons
> > > (Acropora spp.), whereas the remote offshore barrier reef showed
virturally
> > > no survival and no new recruitment (the "virtually" means that whereas
last
> > > year I counted on average over 100 acroporid colonies per 30 x 1 meter
belt
> > > transect, this year I found only one tiny survivor on one transect and one
> > > tiny recruit on the other transect).  The nearshore patchreefs and barrier
> > > reef where recovery is good, are located near the mouth of a large river
> > > and the water in this lagoon area is typically turbid most of the
> > > time.  The remote barrier reef is typically in a pristine ocean
> > > environment, often crystal clear, and subjected to large open ocean swells
> > > much of the year.
> > >
> > > Gregor wrote back to me and qualified his statement:
> > >
> > > "What I was referring to was that in "moderate" bleaching events, when
> > > there was less than say 50% mortality, the inner reefs typically showed
> > > higher mortality than the outer reefs due to mixing at the outer
reefs.....
> > > When it is a" bad" event there is little difference as you have seen in
> > > mortality.  But your observations of faster recovery on the inner reefs
are
> > > interesting and one wonders if this has more to do with a higher number of
> > > nearby parent colonies, water retention in those areas which facilitated
> > > recruitment, rather than with the nutrients being a beneficial stimulus.
> > > But all these are open questions deserving of more research."
> > >
> > > So what is the "global trend"?  Do nearshore reefs or remote barrier reefs
> > > suffer higher mortality and lower recovery rates?  Or should we even try
to
> > > make such a generalization with so many unique factors at each locality?
> > >
> > > Aloha
> > > Bruce
> > >
> > > At 12:33 PM 5/16/2001 -0300, Bernard THOMASSIN wrote:
> > > >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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> > >
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> --
> Dr. Robert W. Buddemeier
> Kansas Geological Survey
> University of Kansas
> 1930 Constant Avenue
> Lawrence, KS 66047 USA
> Ph (1) (785) 864-2112
> Fax (1) (785) 864-5317
> e-mail:  buddrw at kgs.ukans.edu
>
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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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