[Coral-List] Coral diseases and algae

Jack Sobel jack_sobel at verizon.net
Mon Feb 23 17:39:31 EST 2009

Gene Shinn's initial posting on this topic and the responses from Alina
Szmant and Tom Goreau to it inspired me to acquire and read the recent
article titled, "Macroalgae Has No Effect on the Severity and Dynamics of
Caribbean Yellow Band Disease." (Ivana Vu et. al, 2009, published in PloS
Feb 09 Vol 4 Issue).  While I agree that it is a worthwhile contribution to
this subject and to the literature, it is hardly a refutation of the
well-documented concept that removing fish and invertebrates that eat
macroalgae, can lead to proliferation of macroalgae, which in turn can lead
and/or contribute to a decline in coral health. This concept is hardly
rocket science and should be viewed as acting synergistically with other
impacts rather than exclusive of them.

Despite the unfortunate title of this article, it provides no proof that
fish and invertebrate removal, resulting in macroalgal proliferation, is not
a contributor to the decline in coral reef health.  Nor does it even prove
that such removal plays no role in Caribbean yellow band disease (YBD)
outbreaks or proliferation, let alone any other disease impacts. Tom
Goreau's prior response touched on some of the evidence for links to other
diseases.  However, even with respect to YBD, there are limits to what you
can conclude about the role of fishing based on this study.

To their credit, the authors of the study recognized some of their study's
limitations. They certainly recognized that their study precluded contact
between the macroalgae and the coral being studied, and that previously
documented "negative algal effects in natural settings are due to abrasion,
shading, overgrowth, and other related mechanisms". They deliberately did
not focus on such mechanisms, but rather on the roles of benthic macroalgae
"acting as pathogen reservoirs or vectors or by increasing dissolved organic
carbon (DOC)."

In their study, they showed that although the algal treatments increased DOC
in the immediate vicinity of the algal packets, this increase was localized
and could not be detected nearby at the corals being studied.  Can we rule
out a DOC mechanism, if the treatment did not raise DOC around the corals?
They clearly recognize this limitation in their discussion where they argue
that "Understanding the role of these and other environmental factors in
regulating a mechanistic link between algae and DOC is clearly an important
(and neglected) step in understanding what effects macroalgae might have on
corals on coral disease via DOC release."

Similarly, with respect to "the role of benthic macroalgae acting as
pathogen reservoirs or vectors", the experimental design may have also
limited the ability to pick up such a role by (1) preventing contact between
the macroalgae and corals and (2) refreshing the algae to prevent
senescence, etc.

So, I think I would agree with Gene that additional research is needed in
this area, but I think it would be premature to conclude that removing fish
and invertebrates from coral reefs is not having an impact on coral reef
health, given the large amount of evidence supporting this "mantra", or even
to conclude that it is not playing a role in disease generation and/or

Jack Sobel
4910 Earlston Drive
Bethesda, MD  20816
Phone: (301)320-0880
Cell: (202)262-6926     
Email: jack_sobel at verizon.net

-----Original Message-----
   2. Coral diseases and algae (Thomas Goreau)
Message: 2
Date: Sun, 22 Feb 2009 20:29:39 -0500
From: Thomas Goreau <goreau at bestweb.net>
Subject: [Coral-List] Coral diseases and algae
To: coral-list coral-list <coral-list at coral.aoml.noaa.gov>
Cc: Gene Shinn <eshinn at marine.usf.edu>
Message-ID: <AA096B38-260A-4670-B3D9-E1311AE7174A at bestweb.net>
Content-Type: text/plain;	charset=US-ASCII;	format=flowed;

Dear Gene,

When I first began photographing YBD in Jamaica in 1987 we thought it  
was delayed recovery from bleaching, and it took Craig Quirolo five  
years to convince me it was a disease. Discovery Bay nutrients reached  
eutrophic levels in the early 1980s, long after overfishing had taken  
its toll, and the corals were being overgrown with algae.  On those  
corals that were part of my long term coral growth monitoring study, I  
would systematically weed back any algae that could overgrow the  
corals, and it made no difference to the corals with YBD, just as the  
new paper suggests.

By the way the effect of overfishing in Jamaica was not to eliminate  
herbivorous fish, as top-down dogmatists would have us believe, but  
precisely the opposite. In the early 1950s the reef was dominated by  
predatory and invertebrate eating fish, and there were very few  
herbivorous fish. After overfishing and coastal eutrophication the  
fish population switched to overwhelmingly herbivorous species,  
because that is all the food there is now. So the problem is not lack  
of grazers at all, but that the over-fertilized algae grows so fast  
that no grazers can control them.

However I am not sure this lack of obvious algae interaction applies  
to other coral diseases than YBD. Jennifer Smith and colleagues, and  
Maggie Nugues and colleagues, have made convincing cases for possible  
interactions of coral disease pathogens and algae based on lab  
experiments and small scale field associations. We found very strong  
associations between many diseases and certain algae quite  
unexpectedly from data analysis of large scale studies of coral reef  
health in the Turks and Caicos Islands. All the coral diseases that  
were abundant enough to be tabulated at all sites (White Plague, Black  
Band Disease, Gorgonian Disease) were significantly associated with at  
least one algae genus. However YBD was too rare there to  

For the detailed non-parametric statistical correlations based on  
extensive ecological assessment of 26 ecological and environmental  
parameters at 47 sites, including those between algae and coral  
diseases, see the first paper and appendices at:
http://globalcoral.org/Turks and Caicos Islands Coral Reef Health  

Best wishes,

Thomas J. Goreau, PhD
President, Global Coral Reef Alliance
Coordinator, United Nations Commission on Sustainable Development  
Partnership in New Technologies for Small Island Developing States
37 Pleasant Street, Cambridge MA 02139
goreau at bestweb.net

> Date: Fri, 20 Feb 2009 09:53:51 -0500
> From: Eugene Shinn <eshinn at marine.usf.edu>
> Subject: [Coral-List] Do corals need fish to remain healthy?
> To: coral-list at coral.aoml.noaa.gov
> Message-ID: <a0623090bc5c34a2c6813@[]>
> Content-Type: text/plain; charset="us-ascii" ; format="flowed"
> The Program Manager at the Florida Keys National Marine
> Sanctuary  recently made me aware of a new paper titled, "Macroalgae
> Has No Effect on the Severity and Dynamics of Caribbean Yellow Band
> Disease." Ivana Vu et. al, 2009, published in PloS Feb 09 Vol 4 Issue
> 2. The paper is the result of an ingenious  manipulative field study
> in Puerto Rico. As the title implies it shows, that various
> Macroalgae have no effect on CYBD in Montastraea faveolata . This
> conclusion contradicts the widely repeated mantra that these algae
> stimulate coral disease by serving as a reservoirs of pathogens  and
> that their proliferation on reefs is due to removal of herbivorous
> fishes. In other words, remove fish (overfishing) that eat algae and
> the algae will grow and cause decline of coral.
> When I read the paper I was reminded of a recent conversation with
> Harold Hudson of Reef Tech  who described to me what he recently saw
> in Roatan. "It was the biggest healthiest staghorn coral forest I
> have seen in many years", he said.  What caught his eye also was that
> there were essentially no fish! Not even the ubiquitous Damsel fish
> that normally thrive among staghorn branches. It was wonderful to
> hear that such healthy staghorn fields still exist but isn't it odd
> that it is thriving  without the usual tropicals, surgeon, and parrot
> fish? Similar observations have been recorded by J. Keck et al.,
> "Unexpectedly high cover of Acropora cervicornis on offshore reefs in
> Rotan (Honduras)" published in Coral Reefs, DOI
> 10.1007/s00338-005-0502-6  and also confirmed in a paper by B. Riegl
> et al, Offshore refuge and metapopulation resilience explains high
> local densisty of an endangered coral (Acropora cervicornis). In
> Marine Pollution Bulletin.  Many of us can remember the luxurious
> corals on the North coast of Jamaica before the early 1980s at a time
> when the area had already been fished out. Apparently what ever
> started the general Caribbean decline in the late 1970s and early
> 1980s remains  somewhat elusive but widespread.  I suggest we need
> more straight-forward in-the-field experiments such as the Puerto
> Rico study cited at the beginning.  May be we should  rethink the
> commonly cited association between fishing and coral health??  Gene
> -- 
> No Rocks, No Water, No Ecosystem (EAS)
> ------------------------------------  
> -----------------------------------
> E. A. Shinn, Courtesy Professor
> University of South Florida
> Marine Science Center (room 204)
> 140 Seventh Avenue South
> St. Petersburg, FL 33701
> <eshinn at marine.usf.edu>
> Tel 727 553-1158----------------------------------
> -----------------------------------


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