[Coral-List] Michael Risk - C. delitrix as measure of bioerosion

Michael Risk riskmj at univmail.cis.mcmaster.ca
Tue Oct 17 17:22:46 EDT 2006


If you guys are going to keep asking hard questions, I'm going to stop

But perhaps on a more serious vein: I will very quickly reach the end
of my knowledge limits here. I really don't know a lot about this.
Perhaps no one does. To rant on a bit more: EVERY coral reef scientist
should be aware of the fact that bioerosion is at least half the
carbonate balance on reefs. I invite -list members to perform the
following experiment: pick a journal, any journal that publishes
reef-related work. Score papers on bioereosion versus those on corals,
MUCH LESS than half the budget. It is a depressing example of the
collective application of scientific blinkers.

I will try to answer your questions, but will be grasping at straws.

Baseline values: Depends on whether "baseline" means pre-human, or
nutrient-poor: these two are not always the same. From the cross-shelf
studies that have been done, we know that bioerosion rates increase
across the shelf. The assumption has been that this is nutrient-driven,
and changes in the cast of characters amongst the bioeroders would seem
to bear this out. One could argue, for example, that the "proper"
bioerosion rates on the GBR would have Magnetic Island with the same
values as Myrmidon-if you took away the continent.

Thing is, pre-human values will be hard to estimate, because the
evidence is all chewed-up. Evan Edinger has made some valiant attempts
in a couple of his papers. Experimental values are notoriously
undependable: initial bioerosion is very high, but then it levels off. 

In short: I don't know. We are dealing with a very old
process-PreCambrian oolites have algal borings!

LOcal variation is quite high. First of all, on a given reef, backreef
regions will be more heavily hit. The assumption again has been that
this is due to increased nutrients, bacterial regeneration, etc. CCA
substrates are often quite clean, save for algal borings.

Of great interest to me is interspecific variation. As I noted earlier,
Montastrea cavernosa is teh favorite target of Cliona delitirx. Perhaps
it is too busy catching zooplankton to notice? But there is huge
variation in other species. C. laticavicola loves Acropora-or did,
while there still was Acropora.

Many years ago we did a small study on some corals from Tobago. A
recent hurricane had given us a supply of dead corals, whose demise
could be dated. We were also able to get our hands on some older

We scored the sponge fauna in each coral species. There were marked
preferences. We then looked at the sponges in dead corals-and the
community converged. In other words, there are allelopathic reactions
going on at the cellular level among coral and sponge species-once the
coral dies, then the race is to the swiftest.

BUt basically, I haven't a clue.


On Tue, 17 Oct 2006 16:42:02 +0000
 "Dr. Stephen Jameson" <sjameson at coralseas.com> wrote:
> Dear Mike,
> Thanks for the coral-list note regarding:
> > Back to The Destroyer. Christine Ward-Paige and I devised a
> > quick-and-dirty scheme for FMRI by which amounts of C. delitrix
> could
> > be estimated. Nothing special, a diver simply swims a transect line
> > with a quadrat frame (25x25cm divided into 5x5cm squares works
> well),
> > estimating area of delitirix. This takes next to no time. The
> problem
> > with converting these measures to estimates of framework
> destruction is
> > that colonies of delitrix are not two-dimensional. It frequently
> drives
> > straight into the heart of the coral. Rose and Risk gives some idea
> of
> > the variance involved in estimating rates from areas-but areas are
> a
> > start, and it?s easy. Delitrix does not occur in the Indo-Pacific.
> In our bioindicator review paper in the "Internal Bioeroders" section
> (which can be downloaded at <www.coralseas.com/press.html>:
> Jameson SC, Erdmann MV, Gibson Jr GR, Potts KW (1998) Development of
> biological criteria for coral reef ecosystem assessment.  Atoll Res
> Bull,
> September 1998, No. 450, Smithsonian Institution, Washington, DC, 102
> pp
> we provide the following summary and recommendation regarding Cliona
> research.
> ***
> Internal Bioeroders
> Of the above mentioned eutrophication bioindicators, one group,
> internal
> bioeroders, have been thoroughly investigated and have demonstrated a
> consistent, graded response of increasing abundance with increasing
> eutrophication on reefs (Rose and Risk 1985, Sammarco and Risk 1990,
> Risk et
> al. 1995, Holmes 1997).  Holmes (1997) found that the proportion of
> dead
> coral rubble invaded by clionid sponges, as well as the number of
> invasions
> per rubble sample, increased dramatically with increasing
> eutrophication on
> reefs of Barbados.  Rose and Risk (1985) found similar results with
> Cliona
> infestations of live Montastrea cavernosa heads in the Grand Caymans,
> while
> Sammarco and Risk (1990) and Risk et al. (1995) suggested that
> distinctive
> cross-continental shelf patterns of bioerosion (by sponges and
> bivalves) in
> Porites and Acropora on the Great Barrier Reef were explained
> primarily by
> increasing organic input with proximity to the mainland.
> Research recommendation:  Though this group has not yet been formally
> proposed for inclusion in biomonitoring programs, results of the
> above
> research suggest that internal bioeroders provide a sensitive
> assessment of
> increasing eutrophication on reefs and that development of a rigorous
> bioassay could be accomplished with minimal additional research.
> ***
> Mike Questions:
> 1.  Have you given any thought as to what would be appropriate
> reference
> conditions (concentrations in minimally impaired environments) for
> the
> various Cliona species in their respective geographical locations
> throughout
> the world?
> 2.  In minimally impaired conditions, does their concentration vary
> in
> different coral reef zones?
> Best regards,
> Dr. Stephen C. Jameson, President
> Coral Seas Inc. - Integrated Coastal Zone Management
> 4254 Hungry Run Road, The Plains, VA  20198-1715  USA
> Office:  703-754-8690, Fax:  703-754-9139
> Email:  sjameson at coralseas.com
> Web Site:  http://www.coralseas.com
> and
> Research Collaborator
> Smithsonian National Museum of Natural History
> Washington, DC 20560

Mike Risk
Marine Ecologist
PO Box 1195
Durham Ontario
N0G 1R0

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