I think you need to take one step back. What do you hope to learn from
your "hardness" measurements? It seems that you're interested in the
resistance of organisms to being "chewed" by predators. In which case
hardness is not appropriate and you have to take into account not only the
fracture properties of the integument but the shape of the teeth in the
predator's mouth / nature of the gastric mill / characteristics of any other
appendage which might be used to break open the prey item.
So . . . why do you think you need to make these measurements?
Julian VIncent
Quoting Peter Keen <[log in to unmask]>:
> Hello,
> I've had an inquiry from a doctoral student who wishes to determine
> the
> hardness, relative or otherwise, of the integument of zooplankton that
> form
> the natural prey of crayfish phyllosoma. She originally proposed using
> a
> penetrometer but the ones available to her were far too large and it's
> my
> feeling that they all will be given the scale of her test subjects
> which
> range from a few millimetres to a couple of centimetres. We've
> considered a
> surface hardness instrument such as used for testing metal surface
> coatings
> but she was concerned that the storage of samples until returning from
> her
> sample collection cruise would affect the properties of the integument,
> and
> the instruments available to her cannot be taken on board the ship for
> testing while fresh. Another suggestion was to treat sorted samples in
> bulk
> and dissolve the calcium carbonate fraction away with EDTA to
ascertain
> the
> % compostion ratio by weight which may be useful for the crustaceans
> but
> perhaps not for other species. Prey species include copepods, salps,
> and
> fish larvae. I'd appreciate any ideas anyone might have on this topic
> that
> we could explore prior to her departure on the sample collection cruise
> in
> mid-march. I look forward to responses with interest.
>
>
> Best Regards
>
> Peter Keen
> University of Auckland,
> School of Geography and Environmental Sciences
> Phone: 09 3737 599 ext 88536
> e-mail: [log in to unmask]
> http://www.auckland.ac.nz
>
>
> Best Regards
>
> Peter Keen
> University of Auckland,
> SGES
> Phone: 09 3737 599 ext 8536
> e-mail: [log in to unmask]
> http://www.auckland.ac.nz
>
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