[Coral-List] Corals, algae, and bacteria

Thomas Goreau goreau at bestweb.net
Thu Jun 15 12:44:14 EDT 2006

The following exchange on the role of algae and bacteria in coral  
reef degradation may be of interest to some readers. As usual I will  
be out of reach in the field and not able to reply for a long time.

Thomas J. Goreau, PhD
Global Coral Reef Alliance
37 Pleasant Street, Cambridge MA 02139
goreau at bestweb.net

 > Dear Dr. Goreau,
 > I'm a writer with Science magazine and I'm working
 > on
 > a news story for
 > our website on a paper coming out in Ecology
 > Letters.
 > Researchers show
 > that algae indirectly lead to coral death by
 > fostering
 > microbial
 > activity.  Please find the manuscript attached.
 > I wondered if you'd be willing to share your
 > thoughts
 > on these findings
 > as an outside researcher - how novel you believe
 > them
 > to be and what
 > implications they might have.  If you have the time
 > to
 > chat, please let
 > me know a convenient time to reach you, preferably
 > at
 > some point
 > tomorrow.
 > I look forward to hearing from you.
 > Best,
 > Katie Unger
 > Katie Unger
 > News writer
 > Science magazine
 > (202) 326-7089
 > kunger at aaas.org
 > >>> Tom Goreau  06/08 7:53 AM
 > >>>
 > Dear Katie Unger,
 > To my surprise I am now in a place where I can
 > receive
 > and send email, and woke up very early with time to
 > read the paper you kindly sent before diving all
 > day.
 > I'd like to comment a little further on it. This
 > paper
 > uses new methods (both experimental and analytical)
 > to
 > look at algae coral bacterial interactions, and
 > provides much new insight that could not have been
 > reached previously. However the patterns found are
 > very complex, and not all of them fit the author's
 > generalizations. Much more work along these lines is
 > clearly needed.
 > Previous work by Kline and Rohwer has clearly shown
 > that metabolizable sugars and organic commpounds
 > lead
 > to increased bacterial growth on corals, providing a
 > potential mechanism to explain these results. What
 > the
 > exuded organic compounds are, and their effects, are
 > likely to vary greatly between algae, bacteria, and
 > coral species.
 > In my view the conclusions of the paper need to be a
 > little more careful, because of the wide range of
 > patterns they found, which do not fit a single
 > mechanism. It is imortant to realize that these have
 > application to the death of corals that are directly
 > overgrown by corals, some of which appear in the
 > field
 > to die soon after overgrowth, while others appear to
 > remain alive for a long time, even though they are
 > bleached for lack of light (I say this from decades
 > of
 > experience weeding algae off corals).
 > But I think that the conclusions need to be tempered
 > by the following:
 > 1) There is no field evidence that corals die back
 > in
 > portions of the coral that are not directly
 > overgrown,
 > so this supports a mechanism of mortality inducecd
 > by
 > direct interaction or the indirect effects of
 > shading,
 > not that there is a distance effect stimulating
 > bacteria to kill corals not directly contacted by
 > algae. In eutrophic (nutrient rich) reefs we see the
 > last tips of corals remaining healthy and normaly
 > colored even after almost all the colony has been
 > smothered and killed. So I do not see the sort of
 > runaway positive feedback of algae killing corals
 > faster, that they imply. Furthermore in reefs where
 > we
 > have been able to eliminate land-based sources of
 > nutrients to reefs the algae very quickly die back,
 > and the corals recover, although this takes much
 > longer.
 > 2) I do not think that this has any relationship to
 > coral disease. Disease is not mentioned except where
 > they quote our older papers mentioning that both
 > algae
 > overgrowth and diseases have greatly increased (but
 > not further alluded to in the conclusions). While it
 > is true that both are increasing, we sill see no
 > correlation between disease and eutrophication
 > phenomena in the field at all!  I saw many reefs
 > smothered and killed by algae in areas near
 > land-based
 > sources of nutrient polllution long before diseases
 > became a problem. Conversely we see in the field
 > patchy areas of very high incidence of coral
 > diseases
 > that can be found in areas with essentially no algae
 > as well as those that are being smothered. In fact I
 > have been looking at both kinds of sites here in the
 > Turks and Caicos reefs in the last few days, and
 > have
 > seen the same in many other parts of the Caribbean,
 > Indian Ocean,  Pacific, and Southeast Asia.
 > Best wishes,
 > Tom
 > Thomas J. Goreau, PhD
 > President
 > Global Coral Reef Alliance
 > 37 Pleasant Street, Cambridge MA 02139
 > 617-864-4226
 > goreau at bestweb.net
 > http://www.globalcoral.org
--- Katie Unger <kunger at aaas.org> wrote:

 > Dear Tom,
 > I very much appreciate your taking the time to read
 > and comment on this
 > paper.  Unfortunately, our deadlines with these
 > stories are very short,
 > and the story actually went up on the web last
 > night!  Please find a
 > link to it here:
 > >
 > > I do hope we get a chance to speak at another time.
 > Best,
 > Katie

Dear Katie,

This is unfortunate because the ecological
observations really don't support the broad
conclusions of this paper, as Bruno rightly points
out. The coral reef literature is full of this sort of
overextended conclusions, and once these sorts of
things appear in Science and Nature, those who have
not made any observations themselves take them as
gospel truth.

Best wishes,

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