[Coral-List] Algae and nutrients and herbivory in oligotrophic waters

Dean Jacobson atolldino at yahoo.com
Fri Jun 20 00:25:38 EDT 2008

Dear lister:

Tom's response reminded me of a dive this week.  On Wednesday I was revisiting a site that was devastated by COTS several years ago, Irooj Island next to the northern pass on Majuro atoll, a location far from human source of pollution.  I had expected the thick cyanobacteria and Dictyota bloom that followed predation on coral to have diminished after three years, but to my surprise the algal biomass is as thick as ever. No coral have recruited, other than the most shallow substrates that are free of algae. Yet an identical COTS-devasted patch reef just a few hundred meters to the west is free of algae, and dead coral surfaces are thick with young Acropora recruits.  I am guessing an eddy forms around Irooj (where there is a "dead end" corner next to the pass) and has trapped the nutrients.  There appears to be many herbivorous fish, but in seven years I have never observed any grazing on Dicytota.  So, I concur with Tom Goreau's observations on bottom-up

Also, have witnessed local scarids avoid live coral, as well, as well as bit-marking a minority of Porites colonies.

Cheers, and looking forward to meeting some of you at ICRS,
Dean Jacobson
College of the Marshall Islands

--- On Wed, 6/18/08, Thomas Goreau <goreau at bestweb.net> wrote:

> From: Thomas Goreau <goreau at bestweb.net>
> Subject: [Coral-List] Algae and nutrients and herbivory in oligotrophic waters
> To: "Imam Bachtiar" <ibachtiar at telkom.net>
> Cc: "coral-list coral-list" <coral-list at coral.aoml.noaa.gov>
> Date: Wednesday, June 18, 2008, 10:06 AM
> Dear Imam,
> Very few of the studies on herbivory and algae are any
> good, because  
> only a tiny handful have made accurate nutrient
> measurements. When  
> this is done properly it is clear that nutrients drive
> algae  
> productivity and herbivory is only a secondary factor,
> because  
> grazers prefer to eat some species and avoid others.
> I've looked at  
> the zonation of algae species in reefs all around the world
> and these  
> are sharply zoned by nutrients in ways that clearly reveal
> the  
> sources. Every place I've looked with nutrient sources
> are dominated  
> by algae whether or not herbivores are present (and
> herbivore always  
> dominate the fish where there are nutrient sources, whether
> these are  
> from human land-based sources or from upwelling), and algae
> are  
> absent or rare where there are no nutrient sources, again
> whether or  
> not there are herbivores (which there rarely are).  This is
> the exact  
> opposite of what top-downers predict.
> As far as coralivores go, I also think the popular
> conceptions are  
> often erroneous. Most alleged coral eating is much less
> than is  
> claimed. Butterflyfish mostly just suck off surface mucus
> and there  
> is little or no physical damage to polyps. Parrotfish that
> are  
> allegedly biting coral are almost inevitably biting algae
> growing on  
> dead coral, and avoiding the coral tissue, as you can see
> if you look  
> closely where they bite. The popular claims that parrotfish
> eat coral  
> is probably largely untrue, and much of their biting of
> corals is  
> really territorial marking the boundaries of breeding
> territories  
> rather than for food. Almost every time you look where a
> bumphead  
> parrotfish or Napoleon wrasse has bitten into large bubble 
> coral  
> colonies, you will see the tubes of the burrowing clams and
> worms  
> inside the coral that they were really eating rather than
> coral tissue.
> I'll talk a bit about this at the next Gili Trawangan
> workshop in  
> early December. Look forward to continuing to work with you
> there and  
> other sites around Lombok. My best to all my friends in
> Bogor.
> Best wishes,
> Tom
> Thomas J. Goreau, PhD
> President
> Global Coral Reef Alliance
> 37 Pleasant Street, Cambridge MA 02139
> 617-864-4226
> goreau at bestweb.net
> http://www.globalcoral.org
> Date: Wed, 18 Jun 2008 11:28:37 -0700
> From: "Imam Bachtiar"
> <ibachtiar at telkom.net>
> Subject: [Coral-List] Herbivory on oligotrophic waters
> To: <coral-list at coral.aoml.noaa.gov>
> Cc: coremap2 at yahoogroups.com
> Message-ID: <000801c8d171$226bd120$67437360$@net>
> Content-Type: text/plain;	charset="us-ascii"
> Dear all,
> Herbivory is thought to be a key process in coral reef
> resilience.  
> Several
> studies have shown its importance in controlling macroalgae
> and provide
> space for larval settlement. Most papers discussing about
> herbivory
> exclusion experiments, however, do not clearly explain
> whether the  
> location
> of study is oligotrophic or mesotrophic. Some other papers
> also indicate
> that nutrients is not limiting factor of macroalgae growth.
> I would like
> therefore to have your opinion or comments about this.
> 1) Is there any paper studying herbivory in oligotrophic
> waters?
> 2) Which one is more important in reconstruction of reef
> communities in
> oligotrophic waters: herbivory vs corallivory?
> Looking forward to have your reply.
> Best regards,
> Imam Bachtiar
> Postgraduate School
> Institut Pertanian Bogor, Indonesia
> _______________________________________________
> Coral-List mailing list
> Coral-List at coral.aoml.noaa.gov
> http://coral.aoml.noaa.gov/mailman/listinfo/coral-list


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