[Coral-List] positive effects of algae on corals
John Bruno
jbruno at unc.edu
Fri Nov 9 22:56:31 EST 2007
First, Thanks to everyone who sent me examples of macroalgae
benefitting corals. It was very helpful and interesting.
> 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
James, I am an admitted pathological optimist. But no, I am not
advocating anything of the kind. I was simply asking for examples of
positive effects of algae on corals (it's called facilitation and it
is a really common and important ecological phenomenon-certainly
nothing to be afraid of), nothing more. I am writing a paper
describing such a result and was curious what else had been done or
observed in this area.
I have done a lot of non-reef work on facilitation and how
environmental conditions can cause species interactions to switch
between net positive and negative. Anyway, I have been thinking
about some of this in the context of reefs and reef phase shifts, etc.
> 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" ?
Well no, I think I was just asking a question, not making a statement
of political conviction. But since you bring it up, it is an
interesting idea. I was not aware of it until a few listers sent me
links and new stories, but apparently Laurence McCook of the GBRMPA
has been talking and thinking about this for nearly a decade: http://
www.reef.crc.org.au/publications/news/news143.html
We do know that algae usually don't harm adult colonies and that
bleaching and disease are the main drivers of coral losses in many
regions of the world. But the sticky part is that algae would reduce
recruitment, so no, off the top of my head, I don't see this as a
solution. But if there ecologically relevant positive effects of
seaweed on corals, we really should understand them-I would think,
for example, such information could help to parameterize the types of
reef dynamics models that Peter Mumby has been working on.
>
> 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?
Ill assume you know I was not saying that. But I will point out, so
far, nobody has described a case where the restoration of herbivores
did not lead to rapid and near complete macroalgal reductions. But I
really want to hear about counter examples. If you know of one,
please share.
Thanks again James et al.
JB
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