Debate Over Future of Coral Reefs

Ove Hoegh-Guldberg oveh at
Wed Jan 19 02:50:38 EST 2000

>From Ove to Terry re: Planet Ark, Reuters and climate change

Dear Terry,

I felt as you and I were somehow on supposed opposite sides of an issue
that I should throw my thoughts in.  As is clear from your e-mail, this
issue is a "pseudo" debate - our opinions are (surprise surprise) very
similar. Rather than level blame at Planet Ark, I feel fault lies with the
original press dispatch produced by Reuters.  Not only was this inaccurate
but the way it was conceived stank of an attempt to deliberately stir up
controversy (where there is probably little among most).  Perhaps the
Reuters journalist may have only had a minimal grasp of the issues.  
However, the effect was the same and not particularly useful.

Re:  The climate-bleaching debate.

I have always felt that the issue came down to two things - adaptation (we
can forget acclimation I feel for reasons outlined before) and gene flow.
You seem to share that perspective.  And I do agree that we must be
cautious in how we present current and future states of the GBR. Clearly
saying that the GBR will be destroyed next year or five is folly.  
However, and this is the probably the major point of the Mar Freshwater
Research review, if rates of warming are as fast as most climatologists
are measuring and project then substantial changes for the GBR are looming
within decades.  Given that we know virtually nothing about rates of
migration from one latitude to another, or indeed rates at which a heat
sensitive coral clone might increase within a population under a
continuous and increasing heat selection, I feel we have to be cautious.  
Especially given that the stakes are so high.  Granted - genetic variety
and resilience are likely to be factors in shaping the outcome of warming
seas.  Again - this was discussed. How they will act to shape the outcome
will depend on how fast water temperature continue to change.  While
adaptation and gene flow are factors for consideration, they cannot,
however, be seen as strong counter arguments to the evidence that seas may
be warming faster than corals and their zooxanthellae can cope.  Not only
is evidence (mere data) slim or non-existent, but biological experience
and reasoning would suggest that substantially and rapidly moving critical
thresholds for thermal tolerance (by as much as 0.2oC per decade!) in
populations of corals are unlikely to occur this fast without massive
changes (mortalities).  The scale of bleaching mortalities in some areas
of the world in 1998 gives us insight (I believe) into what this might
look like.  Naturally, there are some interesting twists to this (- i.e.
how fast can a constrained symbiotic dinoflagellate evolve?  Let us not
forget our protist partner) but we must (as you again agree) acknowledge
that the weight of evidence suggests that coral reefs are likely to be
substantially changed if we continue to undergo warming of the world's
tropical oceans at these high rates.

Other issues:

In some of the responses to the Mar Freshwater Research Review, some
commentators pointed out that the mortality and change as oceans warm are
likely to be represent a minor "blip" in the geological history of corals
compared to events like the Cretaceous boundary event.  No one could
seriously contest that and my article concurs with this point of view.
Corals are likely to and have adapted to changes in water temperature.  
The issue, however, is not if coral reefs bounce back, it is how long it
will take for them to return to normal condition.  If coral reefs are
dysfunctional for even a few decades, the consequences are likely to be
huge for a large number of dependent human uses.  Add to this continued
selection (i.e. temperatures are not just ramping up, they appear to be
continuously rising - at least to the 32oC cap, if it exists) and the time
frame for a return is hazy to say the least.

So - there are my perspectives on this issue.  I am looking forward to
discussing future research collaborations with you and others - especially
on the issue of modeling how a population might change under selection for
heat tolerance.  As I intimated last year, I really feel that modeling
could give an envelope in which one could assess whether (given realistic
generation times, rates of growth, selection regime) the genetic makeup of
a population could change fast enough such that reefs would undergo
genetic change fast enough to keep up with sea temperature change.  The
other angles I would like to pursue is to (a) verify that acclimation is
unlikely to change outcomes and (b) investigate genetic basis for heat
tolerance and variation in corals and zooxanthellae ... with the
infrastructure in the GBRMPA-Heron Island thermal pond setup, there seems
a great opportunity to test these ideas. The students, postdocs and I (at
the Centre) are already embarking on these studies with vigor.


Ove Hoegh-Guldberg
Professor of Marine Studies
Director, Centre for Marine Studies

Seddon (North) Building 82,
University of Queensland
St Lucia, QLD 4072

Phone:  +61 (07) 3365 4333
Fax:      +61 (07) 3365 4755
E-mail:   oveh at
http://  (active after Jan 20).

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