Julian Sprung's email.

Ove Hoegh-Guldberg oveh at uq.edu.au
Thu Sep 14 19:11:14 EDT 2000


Dear Bruce,

Very interesting - I am extremely interested in tracking microclimate variability as you know.  One
thing has struck me (and I have a field observation to back it up) is that these less stressful
microclimates may represent reservoirs of coral and dinoflagellate tissue for regrowth following
bleaching events.  After the 1998 bleaching event, we lost  many corals - Stylophora and Pocillpora
were hit so hard at One tree Island that students who were working on these species had to find
alternative species to work on.  I was convinced that this was akin to a "local extinction event".
To my surprise, almost the same abundance of large colonies of these two species could be found in
surveys done in 2000 as prior to 1998.  The size of the heads made it seem impossible for these
individuals to be the result of settlement and growth over 18 months.  Where did these coral
colonies come from? I suspect that the internal areas of the Stylophora and Pocillopora coral heads
survived (lower light) and that the coral heads that I thought were completely dead in fact
regenerated from these living internal regions.  Could the internal shading provided by coral heads
act as a defence against thermal stress?  Interesting area.

Cheers,

Ove

-----Original Message-----
From: owner-coral-list at coral.aoml.noaa.gov
[mailto:owner-coral-list at coral.aoml.noaa.gov]On Behalf Of Bruce Carlson
Sent: Monday, 28 August 2000 8:15 AM
To: oveh at uq.edu.au; Billy Causey
Cc: Bernard A. Thomassin; coral-list at coral.aoml.noaa.gov
Subject: Re: Julian Sprung's email.


Ove,

Just to add some anecdotal observations I made in Fiji and Palau that seem
to be consistent with your hypothesis:  very small acroporids (better
surface to volume ratio?), and those in the shade under larger colonies were
the few survivors, and on the Suva barrier reef (where the water flow is
strong), one patch of Acropora muricata that I have monitored since 1972 was
bleached in April -- or so it appeared on first inspection.  However, the
undersides of every branch were brown -- apparently a shading effect (by
brown, I mean "normal" in appearance presumably with zooxanthellae present
in large numbers).  Temperature, sunlight and water flow must all have an
effect.  I recorded this on video tape.  I did not notice this on any of the
bleached corals on the outer barrier reef where mortality among acroporids
approached 100%. I will check this colony again in November to see if it has
recovered.

Unrelated to bleaching, the Suva barrier reef has been overgrown by
Sargassum since 1972.  I first noticed it growing around the corals in 1995,
but this year it has taken over on top of the reef (I have photos showing
the progression over the years).  It snags on the Porites cylindrica and has
killed those large old colonies.  The only coral colony free of the
Sargassum was "my" old A. muricata colony.  Presumably the large Stegastes
sp. damsels in that patch are keeping it clean = a small oasis in a "sea of
Sargassum".  Why is the Sargassum taking over?  My first guess would be
increased nutrients over the years from farming, coming down the nearby Rewa
river delta, but over fishing of herbivores may also be a factor.

Bruce

----- Original Message -----
From: Ove Hoegh-Guldberg <oveh at uq.edu.au>
To: Billy Causey <Billy.Causey at noaa.gov>
Cc: Bruce Carlson <carlson at soest.hawaii.edu>; Bernard A. Thomassin
<thomassi at com.univ-mrs.fr>; <coral-list at coral.aoml.noaa.gov>
Sent: Sunday, August 27, 2000 11:13 AM
Subject: RE: Julian Sprung's email.


> Dear Bill,
>
> Interesting comments.  My feeling is that oxygen is involved (either as an
promoter of the
> photoinhibitory production and build-up of active oxygen within the
zooxanthellae - that is, as a
> secondary variable).  We know that thermal stress collapses oxygen
production and increases
> respiration (see papers by Coles and Jokiel: Marine Biology. 1977;
43:209-216, Hoegh-Guldberg and
> Smith - J. Exp. Mar. Biol. Ecol. 1989; 129:279-303 and others). If the
photosynthetic production of
> oxygen is down and respiration is up (and probably, bacterial consumption
up due to decaying
> tissue), then oxygen at night over reefs under low flow (especially on
reefs where corals dominate)
> would be expected to decrease, perhaps to critical levels.  While not a
primary factor, I would see
> this as an important follow on effect.  It may actually be an important
determinant of mortality.
>
> I am interested in following up the aggravating effect of oxygen - it
would be useful if oxygen was
> monitored during the next set of bleaching events.  Perhaps water motion
(over small patches of
> reef) might help ameliorate the ultimate impact of a thermal event.  Just
a thought.  That and
> shading a reef might be useful for managers of small show pieces of reefs.
But - just for those
> journalists our there - this would not be useful for anything more than a
few hundred square metres!
>
> Cheers to all,
>
> 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: Monday, 28 August 2000 1:25 AM
> To: oveh at uq.edu.au
> Cc: Bruce Carlson; Bernard A. Thomassin; coral-list at coral.aoml.noaa.gov
> Subject: Re: Julian Sprung's email.
>
>
> Ove and others,
>
> I am interested in your comments about the role of oxygen.  For years I
have sounded like a broken
> record, exclaiming that while hot water is one of the stressors leading to
coral bleaching, that I
> suspect the slick-calm, doldrum weather patterns lead to a drop in
dissolved oxygen levels in the
> coral
> reef environment, especially at night.  I sometimes think we take the
level of dissolved oxygen on
> coral reefs for granted .... and tend to not believe there could be a
significant enough change to
> affect corals for example.
>
> During years when we have had severe bleaching in the Florida Keys, I have
observed reef fish
> respiring
> very heavily .... in the middle of the day.  So I have often suspected the
oxygen levels as being
> low
> .... during "hot water" events ... even during daylight hours.
>
> Is it possible that the zooxanethellae, existing inside the coral polyp
tissue starts competing with
> the coral polyp for oxygen at night ... when dissolved oxygen levels are
low anyway .... and
> something
> has to give?  Imagine ... day after day and night after night, during
periods of low mixing and
> natural
> aeration of surface waters, the oxygen level drops below a threshold and
the coral polyp is in a
> state
> of competing for oxygen with the zooxanethellae.
>
> Folks ... be kind to me!  I am not a coral physiologist, in fact I wasn't
very good in biochemistry
> .... just a coral reef manager with thousands of hours of observations
that make me think the coral
> bleaching trigger and mechanisms are simpler than we realize.  I am
curious about opinions on this
> idea.
>
> Cheers, Billy Causey
>
> Ove Hoegh-Guldberg wrote:
>
> > Flow probably has some effect through the removal of some of the
feedback effects of the high
> oxygen
> > tensions that occur during the daylight hours.  If the increased
production of active oxygen after
> > thermal stress (a'la Jones et al 1998, reviewed in Hoegh-Guldberg 1999),
then flow might have an
> > ameliorating effect through the decreased boundary layer thickness and
hence oxygen tensions close
> > to coral surfaces.
> >
> > Survival near rivers might be related to the decreased light stress due
to the higher turbidity of
> > rivers.
> >
> > Just some ideas ...
> >
> > Cheers,
> >
> > Ove
> >
> > Professor Ove Hoegh-Guldberg
> > Director, Centre for Marine Studies
> > University of Queensland
> > St Lucia, 4072, QLD
> >
> > Director, Heron, Stradborke and Low Isles Research Stations
> > President, Australian Coral Reef Society
> >
> > Phone:  +61 07 3365 4333
> > Fax:       +61 07 3365 4755
> > Email:    oveh at uq.edu.au
> > http://www.marine.uq.edu.au/ohg/index.htm
> >
> > -----Original Message-----
> > From: owner-coral-list at coral.aoml.noaa.gov
> > [mailto:owner-coral-list at coral.aoml.noaa.gov]On Behalf Of Bruce Carlson
> > Sent: Saturday, 26 August 2000 4:15 AM
> > To: Bernard A. Thomassin; coral-list at coral.aoml.noaa.gov
> > Subject: Re: Julian Sprung's email.
> >
> > Bernard,
> >
> > Did you also notice that corals in areas with swift flowing water
(usually
> > from tides) also survived better than nearby reefs with low flows?  I
> > noticed this in Fiji on the shallow barrier reef of the University of
the
> > South Pacific, and in Palau near the lighthouse reef -- both are similar
> > reef environments with strong laminar water flow (the water is shallow
> > enough to stand up at mid-tide, but the current knocks you over -- I
don't
> > have a more precise current measurement).  Why would flow rate matter?
> > Perhaps there is something related to diffusion rates (which would
increase
> > in strong water flow) which offers some protection during bleaching????
If
> > Ove is right about superoxides forming during warm water events, maybe
this
> > observation is relevant.
> >
> > Also, in Fiji, we noticed that reefs near river mouths also showed good
> > survival rates.  The outer barrier reefs in Palau and Fiji seemed to be
hit
> > the hardest.
> >
> > Bruce
> >
> > ----- Original Message -----
> > From: Bernard A. Thomassin <thomassi at com.univ-mrs.fr>
> > To: <coral-list at coral.aoml.noaa.gov>
> > Sent: Friday, August 25, 2000 6:30 AM
> > Subject: Re: Julian Sprung's email.
> >
> > >
> > > Jonathan.Kelsey at noaa.gov wrote :
> > >
> > > >-Are these generally accepted concepts?
> > > >-Can one accurately assess coral mortality rates associated with a
> > bleachin
> > > >event after "a matter of just a few days"?
> > > >-Are there quantitative studies showing that there is a greater
bleaching
> > > >survival rate among corals in polluted waters versus those in
> > non-polluted
> > > >water? -Any comments and/or further discussion would be greatly
> > appreciated.
> > >
> > > We will presented a poste about the subject at bali meeting. In
Mayotte
> > > Is., North Mozambique Channel, a huge bleaching occurred in 1998
spring
> > > (end of summer season there) and most of 90 percent of the shallow
coral
> > of
> > > the barrier reefs died.
> > > Those corals that surveyed the best are from the muddy environnements
in
> > > bays, on fringing reef fronts and patches, even the harbour !why ?
Because
> > > the corals living in oceanic cooler waters of the barrier reef belt
(170
> > km
> > > long) are less adapted to tolerate hot waters and high level of light
> > (some
> > > got "sun burns" as table acroporas). In opposite population of corals
> > (same
> > > species) living in neritic coastal waters, in inner areas of the
lagoon,
> > > are genetically more adapted to tolerate : high temperature, turbid
waters
> > > after rainfalls, even falls of salinity. Today in Mayotte, probably
the
> > > recovering ibn coral of the mid-lagoon patch reefs (recruitement) is
due
> > to
> > > larvae coming from these coastal coral populations. These is one of
the
> > > main reasons to protect these "special" reefs in muddy environments
from
> > > all the effects of coastal works (marinas, dredgings, infilling of
> > littoral
> > > for roads, etc...).
> > >
> > > This is a good way for researches.. and from where larvae that recruit
are
> > > coming.
> > >
> > > Bernard A. Thomassin
> > > Directeur de recherches au C.N.R.S.
> > >
> > > G.I.S. "Lag-May"
> > > (Groupement d'Int=E9r=EAt Scientifique Environnement marin et littoral
de
> > > Mayotte")
> > > & Centre d'Oceanologie de Marseille,
> > > Station Marine d'Endoume,
> > > rue de la Batterie des Lions,
> > > 13007 Marseille
> > > 9l. (33) 04 91 0416 17
> > > 9l. GSM 06 63 14 91 78
> > > fax. (33) 04 91 04 16 35 (0 l'attention de...)
> > > e-mail : thomassi at sme.com.univ-mrs.fr
> > >
> > >
> > >
>
> --
> Billy D. Causey, Superintendent
> Florida Keys National Marine Sanctuary
> PO Box 500368
> Marathon, FL 33050
> Phone (305) 743.2437, Fax (305) 743.2357
> http://www.fknms.nos.noaa.gov/
>
>
>
>




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