[Coral-List] Fw: ADMAT - Sea Urchins eating iron cannons and granite blocks...

[Dennis Hubbard]

Interesting observations. I spent two field seasons on Easter Island and
observed what looks like *Diadema* boring into the lava substrate (oriented
both vertical and horizontal). This is all the more interesting as the wave
energy is so high on this side of the island that corals cannot recruit.
Basalt is softer than granite, but harder than limestone. Steel is another
issue.... wow!

On the observation of their covering themselves, this sounds similar to the
bahavior of *Tripneustes* in the Caribbean. Way back when I was still at
West Indies Lab, one of our students tackled the question of why they
covered themselves with trash. I'm a geologist, so this is outside my job
description but my sense is that this is typically attributed to defense as
an urchin covered with grass litter will blend in better.

Anyway, the student cut up a sheet of polarizing material to approximate
seagrass and put it into an in-situ enclosure with urchins. The urchins
picked up the polarizing strips just like grass - I guess you work with
what you have available. The interesting thing is that urchins are made of
high-magnesium calcite that nucleates in one direction only: the c-axis of
crystallographic growth. It turned out that the urchins were oprienting the
strips perpendicular to that axis, in effect cross-polarizing the light.
The result would have been a total blocking of light. The student concluded
that this "uber-shading" reflected a strategy to reduce heat (or some other
factor directly related to light) rather than affecting camouflage or just
looking "new wave".

Nature never ceases to surprise us.

Dennis

On Fri, Jan 11, 2013 at 4:49 AM, boc <boc at aquafact.ie> wrote:

> Hello to all.
>
> I live on the west coast of Ireland where our local small urchin,
> Paracentrotus lividus which occurs over much of the southwest and west
> coasts, creates pits in intertidal pools on limestone pavement in which
> they
> then live. They cover themselves in pieces of shell under which Amphipholis
> squamata can be found. Never thought urchins would work their way through
> granite and steel though!
>
> BOC
>
> -----Original Message-----
> From: coral-list-bounces at coral.aoml.noaa.gov
> [mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of David Evans
> Sent: 10 January 2013 20:49
> To: coral-list at coral.aoml.noaa.gov; rookerj at tamug.edu
> Cc: maritime_archaeology at yahoo.co.uk
> Subject: [Coral-List] Fw: ADMAT - Sea Urchins eating iron cannons and
> granite blocks...
>
> Hello All,
>
> Happy New Year!
>
> I was made aware of an interesting observation from a Marine Archaeology
> list. I thought it would be useful to pass it on here for any further
> input.
> Dr. Simon Spooner of the Anglo~Danish Maritime Archaeological Team (ADMAT;
> www.admat.org.uk ) posted this observation on the Sub-Arch List server (
> SUB-ARCH at ASU.EDU ) about bio-eroding sea urchins ( Reb Rock Boring Sea
> Urchin  *echinometre lucunter*) on a shipwreck off the Dominican Republic,
> boring holes into granite blocks and iron canon cargo at the wreck site. He
> was asking if anyone has experience encountering something similar. I will
> post an excerpt here:
>
> .... a shipwreck off Monte Cristi in the Dominican Republic...
>
> .... we noted an interesting biologic factor and wanted to know if anyone
> on
> the list has encountered such on their surveys.
>
> During the survey we noted that some of the granite blocks (over 60 of them
> part of the cargo) which were in the shallows, less than 3 meters depth,
> water temp arround 80 deg F, had holes "drilled" in them. In addition iron
> cannons which appear to have been new cannons with the touche-holes not
> drilled, also had holes in them. We have proved that these holes were made
> by a particular type of sea urchin, the Reb Rock Boring Sea Urchin or
> Echinometre Lucunter.
>
> -->Has anyone conducted a survey where they have encountered this,
> -->either in cargo or on iron cannons?<--
>
> [additionally: "ADMAT is intending to return to the wreck site this summer
> and i hope we can get some further research on these things as there are a
> number of interesting questions they throw up, like how long to burrow a
> hole and how fast to they breed?"]
>
> Many thanks
> Simon
> Dr. Simon Q. Spooner, BSc, MRICS, PhD, MIfA.
> maritime_archaeology at yahoo.co.uk
> Anglo~Danish Maritime Archaeological Team www.admat.org.uk
>
> \\\\\\\\\\\\\\ END EXCERPTS///////////
>
> I was sure some folks on the NOAA Coral list may have some input.
>
> Thanks!
>
> David J. Evans
>
> Bending Light
> www.refractum.blogspot.com
> davidjevans1818 at yahoo.com
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-- 
Dennis Hubbard
Dept of Geology-Oberlin College Oberlin OH 44074
(440) 775-8346

* "When you get on the wrong train.... every stop is the wrong stop"*
 Benjamin Stein: "*Ludes, A Ballad of the Drug and the Dream*"