[Coral-List] Algae and Nutrients and Herbivory

John Bruno jbruno at unc.edu
Mon Jun 23 12:33:02 EDT 2008

> Date: Sun, 22 Jun 2008 20:06:15 -0400
> From: "Michael Risk" <riskmj at univmail.cis.mcmaster.ca>
> Subject: Re: [Coral-List] Algae and Nutrients and Herbivory

> As a token of this approach, I would like to propose a radical
> hypothesis: that the Diadema dieoff was essentially irrelevant to the
> present decline of Caribbean reefs.

Dear Mike,

Thanks for this broad and I think very insightful post.

I don't think your hypothesis is all that crazy.  It is contrary to  
the idea that algae (and fishing) are responsible for coral loss (via  
disease and bleaching) and that reefs can thus be managed/conserved by  
fisheries regulations that lead to reduced algal cover.  But I agree  
with you.  I don't think that the Diadema die-off had anything to do  
with the contemporary loss of coral cover in the Caribbean.

> Worldwide overfishing seems likely, and has often been suggested. But
> it seems to me that this is a phenomenon in search of a mechanism. If
> the large vertebrates were all fished out centuries ago, why did
> decline start in the 60?s and go into high gear in the 70?s? And why
> world-wide? And why is it that the large, desirable  species are  
> fished
> out first (groupers, snappers, etc), leaving hordes of grazers, as is
> the case in places like Indonesia, yet still the reefs decline?
> (Sometimes people become so desperate they eat scats and rabbitfish,
> yuck, in which case all bets are off.)

I agree completely.  All excellent points.

> Climate change also fails the test. The Caribbean had already lost  
> half
> its corals before the first widespread bleaching.

I largely agree with this point too.  The Caribbean coral loss of the  
1980s occurred during what was, according to Barton and Casey (1) a  
relatively cool period (note that in arguing for the primacy of  
climate change as a driver of coral loss, Lesser et al. 2007 argued  
that white band disease is a form of non-infectious bleaching; if so,  
it must be cold water bleaching).  My only caution is that we have  
seen some (localized) coral loss due to climate/bleaching (e.g., in 98  
and 05), but I agree it is in many locations, a relatively minor factor.

> Disease is for sure a factor-but only post-1980, and diseases also
> often have terrestrial links.

Yup, but I doubt white-band did/does.



1.	Barton, A.D., and Casey, K.S. (2005). Climatological context for  
large-scale coral bleaching. Coral Reefs 24, 536-554.

2.  Lesser, M.P. et al. (2007) Are infectious diseases really killing  
corals? Alternative
interpretations of the experimental and ecological data. JEMBE 346:36-44

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