Dear all

We have sampled several species of starfish and struggle to find
sufficient quantities of muscle tissue inside the organism that could
be used for isotope (d15N and d13C) analysis.  There are of course
the 'muscle' forming the walls of the digestive system, but as this
is in contact with ingested/digested food it is easily contaminated.
As a result we took only the wall (skin, test?) of an arm after
removing all the digestive, reproductive, etc. organs.  The wall
consists of a large percentage of inorganic C (the spines and
ossicles) which could present a problem when it comes to d13C
analysis.  Therefore, the determination of C isotopes requires prior
acid-treatment.  Our usual way of acid treatment of, say, very small
crustaceans involve homoginising the dried sample, acidification with
1% HCl in an Eppendorf tube (about 20 min), and the removal of water
and HCl fumes in a freeze-drier.  We do not rinse the sample (as in
Bunn et al., 1995) as some of the more labile C may be lost. This
should leave us with the organic fraction of the sample.

Is this technique sufficient for isolating the organic C from tissue
that contain large (maybe > 80% CaCO3, I haven't determined the
organic C fraction yet) amounts of inorganic C?  How reliable is the
resulting d13C value?  Will d-values be analogous (or comparable) to
those determined for muscle tissue in other animals, for instance the
muscle of the Aristotle's lantern in the sea urchins?

Any advice from anyone who has determined d13C on starfish is
welcome.

Thanking you in advance,
AJ

AJ Smit
Botany Department
University of Western Australia
Nedlands
Western Australia
6907