Nearshore vs. offshore bleaching

Fri May 18 11:16:38 EDT 2001

Al,
Our field observations and monitoring supports your comments and Peter's
observations.  Water movement and circulation seems to play a major role in the
intensification of the bleaching event in specific areas.  Billy

Alan E Strong wrote:

> ...and tidal currents are stronger promoting increased mixing....
>
> Cheers,
> Al Strong
>
> peter Houk wrote:
>
> > Dear All,
> >       I was finishing up field work on my M.S. thesis at the time of the
> > bleaching event in Palau.  My work was conducted in the Iwayama Bay,
> > secluded lagoon waters nearshore Koror.  I noticed that the large beds of
> > Anacropora were not impacted nearly as much if they were situated along a
> > channel (where runoff enters).  My data shows this as well.
> >
> > Best Regards,
> > Peter Houk
> > CNMI DEQ Office
> >
> > >From: "John Naughton" <John.Naughton at noaa.gov>
> > >To: Bruce Carlson <carlson at waquarium.org>
> > >CC: Bernard THOMASSIN <Bernard.Thomassin at com.univ-mrs.fr>,
> > >coral-list at coral.aoml.noaa.gov
> > >Subject: Re: Nearshore vs. offshore bleaching
> > >Date: Wed, 16 May 2001 11:02:31 -1000
> > >
> > >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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> --
> AES...<><.........<><.........<><.........<><........<><..........AES
> Alan E. Strong
> Physical Oceanographer & Team Leader
>    NOAA/NESDIS/ORA
>    Oceanic Research & Applications Division (ORAD)
>      Marine Applications Science Team
> NOAA Science Center -- Rm 711
> 5200 Auth Road
> Camp Springs, MD 20746
>                     Phone:    301-763-8102 x170
>                     FAX:      301-763-8108
>      Alan.E.Strong at noaa.gov
> http://orbit-net.nesdis.noaa.gov/orad
> AES...<><.........<><.........<><.........<><........<><..........AES
>           .
>
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