[Coral-List] COT current status

Dean Jacobson atolldino at yahoo.com
Sun Jan 18 17:49:17 EST 2009


I am still collecting data as a "post mortem" of the Majuro COTS outbreak (which is still going strong in some spots) and I have possible evidence of the importance of eddies and other local aspects of circulation.  Obviously, these observations do not address the fish grazing aspects of the problem.

1.  I have measured coral recruitment on a half dozen patch reefs south of Irooj Island (near the northern pass) that were devastated by COTS in 2004-2006.  Most lack algal blankets (made of long filamentous cyanos, Dictyota and Padina) and have good coral recruitment on dead table corals, up to 60/m2.  (These recruits are now 1-2 cm in diameter) However, two patch reefs closer to Irooj Island, within a protected eddy circulation (revealed by floating flotsom), are densely carpeted with algae and have very low recuitment (0-3/m2).  By the way, one patch reef immediatly adjacent to Irooj largely escaped COTS predation!

2.  It turns out that a single spot on Majuro has hosted a decades-long COTS population. (A former student, Kilom, recalls that they were abundant back in the late 1980s or 90s).  This is also the only spot where I noticed their "outbreak" abundance prior to the atoll-wide outbreak that first became apparent (as large adults) in 2003-04.  The western-most end of this reef, which I recently snorkeled for the first time, has the greatest coral destruction, by far, on Majuro (it was formerly an Isopora-dominated reef, but over 99% of Isopora is dead, presumably due to COTS.  A few young recruits are being eaten as we speak!)

Since this south-eastern Laura reef is the most leeward, protected of any Majuro shore, it may indicate the importance of eddy-like retention of nutrients that stimulate algae (and perhaps the animals themselves) in sustaining a locally elevated population density.

It appears that the Majuro COTS population is self sustaining (there are now a number of age classes on the reef); other than Ebon, no other RMI atoll has had an outbreak.  This argues against both regional outbreaks (i.e., involoving whole island archipelagos, due to unusual large scale oceanographic conditions) and atoll-to-atoll transmission of larvae.  It seems that local Majuro conditions are to blame.

BTW, The first recent Arno atoll outbreak, now in progress (limited to a few dozen animals detected by SCUBA in each of two sites) seems to be localized to Arno Arno, another leeward, south eastern region.

Dean Jacobson
College of the Marshall Islands

--- On Thu, 1/15/09, Karl & Michele <michka at fellenius.net> wrote:

> From: Karl & Michele <michka at fellenius.net>
> Subject: [Coral-List] COT current status
> To: Coral-List at coral.aoml.noaa.gov, info at crcreef.com
> Date: Thursday, January 15, 2009, 6:23 PM
> Dear coral list and CRC,
> I have been looking at the 2003 CRC info doc on crown of
> thorns at 
> www.reef.crc.org.au/publications/brochures/COTS_web_Nov2003.pdf
> as well as a 
> few other web publications.
> I do environmental assessments in Vanuatu and currently
> there is a COT 
> outbreak on Efate. I am seeking fairly specific references
> to published 
> works on linkages between nutrients, algae and COTs. Not so
> much from a 
> coastal run-off perspective but more related to harvesting
> of herbivores and 
> omnivores in the aquarium trade. Efate has an very active
> fish and 
> invertebrate export. COT outbreaks are occurring in their
> collection areas 
> as well as a number of other areas. I realise there are
> numerous factors at 
> play. Last year this was a fairly heated topic here with
> many differing 
> opinions and official responses denying any connections
> between the trade 
> and COTs. However, both 'outbreaks' continue on
> Efate ...
> I have been asked by a group made up of villagers, ex-pat
> residents, and 
> others seeking answers to these questions to do what I can.
> My background is 
> such that I believe these hypotheses to be true, although I
> have not carried 
> out the research. I trust that others have. After last
> years' mess on this 
> subject I have maintained a fairly low profile but now
> there are many people 
> here that are furious that nothing beyond individual groups
> doing COT 
> removals has been done. So I find myself reluctantly
> re-entering the 
> discussion of trying to persuade players that should know
> better, again. I 
> am not entering that foray again without published
> references.
> I am looking for references on any of the following points.
> I am not looking 
> for an emotional back-and-forth between proponents and
> opponents of the 
> aquarium trade. The coral list has already been used for
> that.
> Pre-outbreak stimuli
> -Quite a bit of research suggests that COTs thrive in the
> presence of
> pollution and algae that ensues. A lot of that comes from
> excessive nutrient
> discharges in areas of run-off, like Mele Bay.
> Moreover, further research suggests that nutrient
> discharges can actually
> stimulate reproduction in COTs, outside of their normal
> spawning times in
> Dec & Jan (when, by the way, COTs should not be
> collected because
> handling can trigger early spawning). Other research goes
> yet further
> and suggests that loss of herbivores and omnivores can
> stimulate existing
> COTs to eat more, and faster. This happens because in the
> absence of
> such fish in particular, there is more algae and especially
> cyanobacteria
> left on the reef. And that brings us back to the first
> point above, that
> COTs thrive in algae conditions. So its really about what
> causes the algae,
> not so much as what causes the COTs directly. There is
> correlation between
> aquarium fish collection and COTs outbreaks with respect to
> the issue of
> the algae. It makes sense. Albeit this has not conclusively
> been shown to
> be cause-effect, only a correlation. It is just my personal
> opinion and the
> opinion of others that actually study
> the matter. There is a heck of alot of 'bad' algae
> around in current fish
> collection areas, particularly in Mele Bay. This might help
> to explain the
> COT explosion on Efate (fish collection and nutrient
> pollution) and possibly
> Santo (some nutrient pollution), but not on Epi.
> -Research is not out yet on pelagic and benthic movement of
> COTs. Some
> people speculate that spawning COTs in Fiji are one reason
> behind the COTs
> here. I find that a bit far-fetched but who knows? I've
> seen juveniles, but
> not anything near larval stages. Could this be the source
> for COTs on Epi? I
> don't really know. The point is that it doesn't
> have to be the same reason
> everywhere. Its a mixed bag, as with most disturbances in
> the marine
> environment. It is also possible that the Epi population
> came from Efate. I
> heard that a few years back it was on Emae, before it hit
> North Efate. From
> Emae to Epi makes sense, but why Emae?
> -It is clear that the Triton shell and the Napoleon are
> natural predators of
> COTs. But is their depletion through local consumption
> enough to explain
> Epi? I doubt it. Its definitely a contributor though.
> Post-outbreak response
> -It is clear however that coral recruitment on COTs
> impacted reefs (or any
> impacted reefs that have lost coral) will decrease if
> hervivores and
> omnivores are in less supply than normal. The algae
> prevents new coral from
> settling. Moreover, dead coral covered in algae breaks off,
> and contributes
> to loose rubble further limiting coral recruitment not to
> mention same
> rubble that moves around in surge which damages surviving
> corals. Thus I
> sincerely believe
> that what we are losing now in terms of coral cover on
> Efate will not come
> back until herbivore and omnivore fish populations return
> to normal. Even
> then it will take a long time, considering all the
> pollution and global
> climate stressors acting concurrently. Even then it may be
> too little,
> too late. That in my mind is potentially a much more
> far-reaching issue
> than determining what is causing the outbreak in the first
> place.
> The latter point is sufficient in my mind to take a good,
> hard look at the
> impacts of the aquarium trade here in Vanuatu.
> Thank you,
> Karl
> **
> Karl Fellenius, Director &
> Michele Dricot, Manager
> Vaughani Shores Vanuatu
> Pangona Estates, Efate
> Postal Box 3158
> Port Vila
> office       +678 29273 (AWARE)
> mobileK   +678 7773329
> mobileM  +678 7773326
> email       VaughaniShores at vanuatu.com.vu
> web         http://www.diveVanuatu.org
> **
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