[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:// 

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.


More information about the Coral-List mailing list