[Coral-List] sea urchin removal to prevent bioerosion

Fri Feb 19 11:10:42 EST 2010

Dear Paul, 
That’s an apropos analogy, comparing the number and size of
gears to the interaction of organisms in an ecological system. I hope you don’t
have it copyrighted… I think the ecological gears are always moving, sometimes
very dramatically when a large gear moves very quickly only in one direction,
like when the Diadema population crashed, or in small increments, such a successful
survival, or failure, of a year class of a relatively dominant organism in an ecosystem.
The ecological gears are always turning, sometime greatly and swiftly and
sometimes slowly and reciprocally creating the illusion of a static ecosystem. However,
after us humans came on the scene in large numbers and with the magic of our technology,
those ecological gears really speeded up and now the system seems to be running
amuck and flying apart. 

On Diadema and bio-erosion, for what it’s worth, I have had
a brood stock of adult Diadema in a shallow 110 gallon tank for about 4 years.
There are about a dozen large limestone coral rocks in the tank. The Diadema go
though a two gallon bucket of dense macro algae every day or two, they roam the
rocks and the tank sides incessantly, and there are absolutely no algae growths
on the rocks or the tank sides. In all this time I have seen no scraping into
the surface of the rocks. Of course there are no other bio-eroders such as
boring sponges or clams or filamentous algae on or in the rocks. And the reef
and a tank are two very different environments.

I made a very interesting observation yesterday. It was day
8 of a larvae rearing run with Diadema. I placed a Petri dish of about 2000
larvae under the dissecting scope, checked them out, and then my attention was
diverted. Maybe 10 minutes later I returned and found that almost all the
larvae were tightly concentrated under the small bright spot of the illuminator.
I experimented with moving the illuminator, separating the two spots on
different sides of the dish, and in every case, the larvae moved to concentrate
in the brightest points of light. To me, this indicates that the larvae are
positively phototropic (a valuable tropism if the larvae need to remain in the
surface waters) and also have the capability for directed movement (a valuable
trait if the larvae need to find and move towards a suitable area for
settlement). I would expect that if the larvae can respond and move toward
light, they would also be able to respond and move toward a biochemical
stimulus as well, although that would be a response to a very variable chemical
gradient rather than light intensity. But this is interesting, especially since
after metamorphosis the early juvenile shows a negative response to light,
indicating a reversal of positive phototropism. 

Martin Moe

----- Original Message ----
From: Paul Sammarco <psammarco at lumcon.edu>
To: Bill Allison <allison.billiam at gmail.com>
Cc: coral-list at coral.aoml.noaa.gov
Sent: Wed, February 17, 2010 2:55:22 PM
Subject: Re: [Coral-List] sea urchin removal to prevent bioerosion

Dear Bill,

Hello.  Well said.  

I think that if one is going to try to change a system, it is best done in
small increments - and only to certain limits.  Ecological communities are
very sensitive, despite our perception of them.  I consider them to be like
Swiss watches, where each population represents a gear.  You can change the
abundance of one population if you'd like - and turn that gear.  In doing
that, some other gears will move very slightly because they are much larger.
Indeed, they will hardly be affected at al.  Others, where the gears are
about the same size, will move at about the same rate.  Others - much
smaller ones, however, will move much faster.  

Plus, even if a system appears to be "out of kilt" to our eyes, in fact -
even if it is "out of kilt", it is probably resting at some sort of
equilibrium.  Thus, if we remove a large component of the community, we
throw it into a highly dynamic disequilibrium.  

This is what the Australians recently found out when they removed all of the
feral cats from Macquarie Island, 100 yrs after their introduction.  40% of
the vegetative cover on the island was rapidly lost because the rabbit
populations, held in check by the feral cats, exploded.  Now the bird
populations are being affected as well (Bergstrom et al., 2009; Casey,
2009).  

Food for thought.  

Cheers,

Paul

Bergstrom, D.M., A. Lucieer, K. Kiefer, J. Wasley, L. Belbin, T.K. Pedersen,
and S.L. Shown.  2009.  Indirect effects of invasive species removal
devastate World Heritage Island.  J. Appl. Ecol. 46:  73-81.  

Casey, M.  2009.  Species eradication backfires big time.  CBS News, Jan.
13, 2009, http://www.cbsnews.com/stories/2009/01/13/tech/main4719190.shtml

Paul W. Sammarco, Ph.D.
Executive Director
Association of Marine Laboratories of the Caribbean (AMLC)

and

Professor
Louisiana Universities Marine Consortium (LUMCON)
8124 Hwy.. 56
Chauvin, LA  70344
USA

Tel:                1-985-876-2489
FAX:              1-985-851-2874
Email:          psammarco at lumcon.edu
Website:    www.lumcon.edu

-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov
[mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Bill Allison
Sent: Wednesday, February 17, 2010 10:54 AM
To: Clement Dumont
Cc: coral-list at coral.aoml.noaa.gov
Subject: Re: [Coral-List] sea urchin removal to prevent bioerosion

There was a effort made to remove control the abundance of
Strongylocentrotus droebachiensis on off Nova Scotia in the early 1980s
followed by a mass mortality in about 1983 that may be instructive. Try
Marine Biology (Mann, Wharton, Scheiberling, others). If I am not mistaken a
retrospective paper on the removal exercise and its conceptual
rationalization concluded that it was misconceived.

On Wed, Feb 17, 2010 at 3:01 AM, Clement Dumont <cdumont at hku.hk> wrote:

> Dear all,
> thank you for all the comprehensive replies from which I learned a lot. My
> initial question, however, remained unanswered. Does anybody is aware of
> report/publication of such removal practice of grazers to protect/restore
> coral reefs (i.e. removal program similar to the crown-of thorns)?
>  I have also a project in Malaysia where the Marine Park rangers remove
> every year the sea star Acanthaster planci in an attempt to prevent
> population outbreaks. However, when I found similar densities of sea stars
> at the sites where removal occur with sites where no sea stars are
> collected. Unthinking removal programs are generally unsuccessful and can
> even further damage the corals (e.g. Japan sea star removal).
>
> Best wishes,
> Clement
>
> ---------
> Date: Thu, 11 Feb 2010 08:54:02 +0800
> From: Clement Dumont <cdumont at hku.hk>
> Subject: [Coral-List] sea urchin removal to prevent bioerosion
> To: "coral-list at coral.aoml.noaa.gov" <coral-list at coral.aoml.noaa.gov>
> Message-ID:
>        <A079DF1679D36540A0B97A14317E122A12B13FA575 at MAIL.hkucc-com.hku.hk>
> Content-Type: text/plain; charset="us-ascii"
>
> Dear all,
> the Hong Kong government took the initiative (based on brief observations)
> to remove every year thousands of the sea urchin Diadema setosum and the
> corallivore snail Drupella sp. to prevent the excessive bioerosion of
corals
> (but no studies have been conducted).. Being really surprised by this
> initiative, I started a cage experiment with different densities of urchin
> to examine whether Diadema is the major factor contributing to bioerosion.
> With no much surprise (the experiment is still running), we have a higher
> recruitment of macroalgae and also higher sedimentation on corals
> non-exposed to sea urchin grazing and even with high densities densities
of
> urchins, still no sign of bioerosion. Hong Kong waters are highly polluted
> and the nutrient enrichment and high sedimentation may rather be the main
> causes of corals degradation.
> I am therefore curious whether such sea urchin removal practice (not on a
> fishery purpose) is/has been conducted elsewhere to prevent bioerosion of
> corals.
>
> Thanks,
> Clement
>
> ----
> Clement Dumont
> Research Assistant Professor
> The Swire Institute of Marine Science
> & The Division of Ecology & Biodiversity
> The School of Biological Sciences
> The University of Hong Kong
> Pokfulam, Hong Kong, PR China
>
> Phone: (852) 51 99 1730
> Webpage: http://web.hku.hk/~cdumont/ <http://web.hku.hk/%7Ecdumont/>
>
>
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> Coral-List at coral.aoml.noaa.gov
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>

-- 
Reality, as usual, beats fiction out of sight.
Conrad, 1915

"Reality" is a dangerous word that should always be incarcerated in
quotation marks.
Nabokov
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