Here's the reference to diatom testing:
Nature 421, 841 - 843 (2003)
Architecture and material properties of diatom shells provide effective
mechanical protection
CHRISTIAN E. HAMM*, RUDOLF MERKEL†‡, OLAF SPRINGER§, PIOTR JURKOJC§,
CHRISTIAN MAIER†, KATHRIN PRECHTEL† & VICTOR SMETACEK*
* Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen
12, 27570 Bremerhaven, Germany
† Technische Universität München, Physics Department (Biophysics Group E22),
85748 Garching, Germany
‡ Research Centre Jülich, Institute of Thin Films and Interfaces, 52425
Jülich, Germany
§ Hochschule Bremen – University of Applied Science, Neustadtswall 30, 28199
Bremen, Germany
Correspondence and requests for materials should be addressed to C.E.H.
(e-mail: [log in to unmask]).
Diatoms are the major contributors to phytoplankton blooms in lakes and in
the sea and hence are central in aquatic ecosystems and the global carbon
cycle. All free-living diatoms differ from other phytoplankton groups in
having silicified cell walls in the form of two 'shells' (the frustule) of
manifold shape and intricate architecture whose function and role, if any,
in contributing to the evolutionary success of diatoms is under debate. We
explored the defence potential of the frustules as armour against predators
by measuring their strength. Real and virtual loading tests (using
calibrated glass microneedles and finite element analysis) were performed on
centric and pennate diatom cells. Here we show that the frustules are
remarkably strong by virtue of their architecture and the material
properties of the diatom silica. We conclude that diatom frustules have
evolved as mechanical protection for the cells because exceptional force is
required to break them. The evolutionary arms race between diatoms and their
specialized predators will have had considerable influence in structuring
pelagic food webs and biogeochemical cycles.
Janine
Janine Benyus
Writer
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Stevensville, Montana
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-----Original Message-----
From: Engineers and biologists mechanical design list
[mailto:[log in to unmask]] On Behalf Of Currey, J.D.
Sent: Thursday, February 27, 2003 2:25 AM
To: [log in to unmask]
Subject: Re: Determining hardness of zooplankton integument
Peter
Your student has a real problem here. However: 'The best is the enemy
of the good' (you know how Julian just loves quotations), and she'll
just have to do the best she can.
I agree completely with what Richard B said. Microhardness will at
least give you something, and microhardness is loosely correlated with
abrasion resistance via Archard's law (it's on the web!). Microhardness
testers are pretty common in engineering departments and reasonably easy
to use. Nanohardness is an order of magnitude more difficult, and
expensive, and not to be recommended except in extremis.
Definitely don't try to treat in bulk.
Freezing in sea water is I think a good idea. Most mineralised tissues
are reasonably forgiving of having been frozen and then thawed.
Preservation in alcohol or formol definitely not a good idea.
Strength of the whole structures of things like copepods could be tested
using small testing equipment, but normalising to compare like with like
would be v. difficult. Fish larvae and salps of course are not amenable
to testing in any sensible way, and hardness is meaningless in their
case, though Julian could probably come up with an ingenious way of
testing their TOUGHNESS.
I read VERY recently of a report, but I'm damned if I can remember
where, of people who had been testing diatom strength using a glass rod
as a load 'cell' They found quite nice relationships, as I remember,
between edibility and various mechanical properties. But all these
kinds of methods will only make sense on hard tissues, not sloppy salps!
A question that occurred to me is whether these prey will have been
partially digested already. If they have, that's an added problem, of
course.
Good luck
John
Professor John Currey
Department of Biology
Area 9
PO Box 373
University of York
York YO10 5YW. UK
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