Iron agaisnt bleaching ?

[MARTIN PECHEUX]

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
bleaching.

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)
for one day : 1h light (under a
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).
Electron transport at PS II Qa-Qb
(measured by relative fluorescence
at 2 milliseconds) was similarly
enhanced.
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,
www.reef.edu.au 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
catastroph.
Good week,

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