[Coral-List] Phase Shift

James Cervino PhD. jcervino at whoi.edu
Fri Nov 9 09:32:12 EST 2007

Hi John,

What type of reef ecosystem are you thinking of? As the reefs from the past (60s
and 70s even into the 80s) were clearly not like the algal-smothered reefs of
today. Are you saying that if all the algal landscapers return to the reefs we
will begin to see a bounce back of all those colonies or that the small numbers
hanging on will now be protected due to shading by the smothering algae? What
are you trying to say here? "that macroalgae can now be a good addition to a
reef system in today's world due to their potential protection and shading
during thermal bleaching events" ?

Also, for clarification, are you saying that its ok for humans to continue to
pump all of the sewage nutrients into carstic limestone coastal zones and that
the macro-algae that proliferates will be controlled by the landscapers?

Thanks John, from James (glass half empty) Cervino :)

Bruno wrote:

First, is anyone aware of an example (preferably published) where
macroalgae have alleviated some stress or otherwise benefited corals
in terms of growth, survival, etc?  I have heard people talk about
observing that shading by macroalgae can reduce bleaching and
bleaching-related mortality, but don't recall seeing any studies on
this and have not been able to dig any up using various search engines.

Second, is anyone aware of an example in which after herbivore
populations were replenished (either naturally or via management)
macroalgal cover/biomass remained "high"?  This question really gets
at whether "phase shifts" to macroalgal dominance are "permanent
states" or simply responses to the removal of top down control.
Every example I can think of clearly indicates that once herbivores
return (e.g., Diadema to the north coast of Jamaica ala Edmunds and
Carpenter 2001, Carpenter and Edmunds 2006) macroalge immediately
return to formerly very low cover and abundance (which also suggests
that top down rather than bottom up forces were the primary cause of
the change in macroalgal cover in the first place).

Thanks for any examples, ideas or advise you might have.


John Bruno, Ph.D.
Associate Professor
Department of Marine Science
The University of North Carolina at Chapel Hill
Chapel Hill, NC 27599-330
jbruno at unc.edu

Dr. James M. Cervino
Pace University & Visiting Scientist
Woods Hole Oceanographic Inst.
Deptartment of Marine Chemistry
Woods Hole MA.
Cell: 917-620*5287

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