Iron against bleaching ? Is iron geritol for corals??

Jim_Maragos at Jim_Maragos at
Thu Dec 23 16:20:19 EST 1999

     Martin Pecheux has provided an informative review (below) that suggests
     that iron enrichment may protect corals from bleaching through iron
     enrichment.  However, enrichment may have the opposite effect- accelerate
     the loss and displacement of living corals and other reef builders from
     bleached and other injured reefs.

     We have a "real world" case study providing evidence for iron inhibiting
     reef recovery- that of a 1993 ship grounding at one of our uninhabited and
     previously pristine reef areas, the Rose Atoll National Wildlife Refuge in
     American Samoa (central tropical Pacific).

     A 250 mt Taiwanese longliner ran aground on the SW perimeter reef of the
     atoll in Oct 1993 and quickly broke up before a salvage tug could reach the
     scene six weeks later.  A 100,000 gallon fuel, 500 gallon oil, and 2,500 lb
     ammonia spill from the wreck fanned out over the SW reefs, killing the
     dominant reef builders: crustose coralline pink algae and reef corals.
     After the acute phase of the spill, the ship began breaking into hundreds
     of smaller pieces, releasing ever-increasing quantities of dissolved iron.
     Dead reef surfaces were invaded by cyanobacteria (bluegreen algae, possibly
     including Schizothrix and Lyngbya) and Jania (a red alga) near the iron
     wreckage.  Although pink crustose coralline algae and stony corals are now
     recolonizing some dead reef surfaces away from the wreckage, the bluegreen
     algae continue to dominate reef surfaces downdrift of the metallic wreckage
     and have spread to other reef areas of the atoll not originally killed by
     the spill.

     Dissolved iron concentrations in the water have been measured both near
     metallic wreckage and away from it, and increase dramatically over the
     wreckage site. Iron concentrations also strongly correlate positively with
     bluegreen algal population densities on the underlying reef surfaces.

     Although the salvage company was payed about $1.2 million by the ship
     owner's insurance company to remove the vessel, the salvage company
     succeeded in removing only a fraction of the vessel (bow section) from the
     reef, and no further compensation has been payed by the responsible
     parties. The U.S. Fish and Wildlife Service has raised its own funds to
     complete removal of ship wreckage from the reef flats by last August and
     will initiate removal of reef slope wreckage in the next few months.  At
     the end of the August cleanup, bluegreen algal populations were noticeably
     declining after removal of metallic debris from the flats, and presumably
     in response to the reduction in water-column iron enrichment.

     Stay tuned because we intend to initiate another round of dissolved iron
     and bluegreen algal measurements in the coming months- after the next phase
     of the cleanup is completed.

     Our Rose Atoll case study raises several concerns with respect to iron
     enrichment as a possible panacea for counteracting the effects of coral

     1) Ship owners and their insurance companies and salvage contractors may
     argue to leave their wrecked vessels on coral reefs (rather than pay the
     large expense of removing them) because iron is "good" for reefs.

     2) If bleaching results in the die-off of corals, cyanobacteria may invade
     the available dead surfaces and actually persist for longer periods-
     because of iron enrichment.

     3) After re-reading Martin's comments, I don't see any evidence from the
     cited laboratory studies that iron itself has actually stimulated
     photosynthesis in bleached stony corals.

     4) Although hypothesis is interesting from a research standpoint, it is
     important to clarify that it is only a hypothesis at this stage- there is
     no positive proof showing that iron aids beleaguered corals.

     5) It is equally, if not more important, to research the potential negative
     effects of iron on coral reefs and add to the evidence that invasive
     bluegreen algae may be stimulated and compete against reef builders for
     space on injured and healthy reefs.  With the increased incidence of vessel
     groundings on reefs, this research could help compel shippers to be more
     cautious around reefs and to legally pay all damage and restoration costs
     associated with groundings.

     Happy Holidays to you all!

     Jim Maragos, Ph.D.,
     Coral Reef Biologist, U.S. Fish and Wildlife Service, Honolulu

     ____________________Reply Separator____________________
     Subject:  Iron agaisnt bleaching ?
     Author:   "MARTIN PECHEUX" <martinpecheux at>
     Date:          12/23/99 11:25 AM

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From: "MARTIN PECHEUX" <martinpecheux at>
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Reply-To: "MARTIN PECHEUX" <martinpecheux at>


Dear all,

There might be PERHAPS a simple way
to act at LOCAL scale against coral
reef mass bleaching : by iron
fertilization at nanomole
concentration. Iron limitation is
said to occur in oligotrophic
waters, mainly for the
photosynthetic apparatus, and
photoinhibition is at root of

Cnidarian respond to nanomole iron
enrichment, as a first experiment
just realised shows me : tentacles
of Anemonia viridis were cut and
incubated in 5ml tubes, with either
no enrichment (n=8), 3nM Fe as
sulfate iron (n=4) and 3uM Fe (n=4)
mild stress of 320uE/m2.s, 29C),
16h dark, 8h light. Photosynthetic
efficiency was measured with a PEA
by fast fluorescence kiFnetics. The
classical stress indicator Fv/Fm
was 0.334 (0.228-0.375) in control,
0.384 (0.345-0.425) at 3nM Fe,
different at p=0.024, and 0.437
(0.393-0.512) at 3uM Fe (p=0.0012).
(measured by relative fluorescence
at 2 milliseconds) was similarly
The figure is similar than with
plankton experiments and ocean iron
fertilisations (Science, 1999, 283,
840-843, Nature, 1994, 371,
143-149, and refs. herein). For
coral reef bleaching, there is now
good convergence to indicate that
it originates at PS II or in the
latter electron chain (Jones et
al., 1998, Plant Cell Env, 21,
1219-1230, Warner et al., 1994, id,
19, 291-299, Hoegh-Guldberg, and refs. herein).
The Fv/Fm bleaching threshold under
light, T and CO2 stresses in 7
experiments with corals and forams
is 0.275+/-0.050 (subm.). Hence the
possibility that local iron
enrichment can protect from
photoinhibition the PS II, cyt
b556, b6-f and/or PS I, and thus
alleviate bleaching.
I know that more theoritical works
would have to be done, primary of
iron concentration in reefs (and
then indication of a relationship
with bleaching or not, that I never
saw, nor the contrary) and in situ
reaction to Fe enrichment measured
by fluorescence. Yet bleaching is
catastrophic and iron enrichment is
not pollutant nor very difficult.
As sulfate iron (FeSO4, 7 H2O, best
diluted before), 2nM Fe is
0.28mg/m3, or 1.39kg per km2  of a
5m depth lagoon. Just to be throw
from a small boat here and there,
or even with a slow leaking can
near the beach, according to local
hydrological conditions, when
bleaching threatens (cf. A. Strong
warning). This is the best
experiment, I guess. Results may
come quickly by comparing different
areas. (If it works, I will sell
you fireworks with rain of sulfate
iron, easy and funny...).
Contact me if you are interested by
the problematic or thinking to do
so. Enrichment raises several
questions but here today is just
given the principles.
Even if effective for a favorite
area, this is a "drop in ocean" in
face of the bleaching global
Good week,

Martin Pecheux
martinpecheux at
Nice University, 15 bis rue des
Roses, 06100 Nice, France
Tel +33 492 071 079

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