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major concentrations are to be found in the leaves, bark, seeds, corms
or nuts.
Since these are the most used portions of the plant for animal
foods, the plants pass the radioactive materials on to the animals
where they are incorporated into the animal tissue, only to be released in the normal biological cycle and passed back to
the
land
for reabsorption.
The invertebrates, or animals without backbones, make
great bulk of the animal life of an atoll.
up
the
The role of these animals in
the cycling of radioactive materials in an atollis as varied as the
invertebrate forms.
Sea cucumbers have been compared with earth
worms in their ceaseless turning of the gravel and sand as they obtain
their nutriment from bacteria and algae.
Corals and clams remove
microorganisms and particulate matter from the water and also
host to the unicellular algae, Zooxanthellae, which are found
tissues.
are
in their
The Zooxanthellae may be thought of as a vast reservoir of
trapped plankton.
understood but
Their relationship to their host is
not
completely
it is probable that they play an important part in the
removal of phosphate wastes.
Corals and clams are eroded by algae
and sponges, which bore holes in the skeleton or shell, thus contri -
buting to a return of carbonates to the water.
Crabs,
sipunculid
worms and others also attack the skeleton of the corals.
land crabs contribute to the deposition of
radioisotopes
Some of the
from
the
sea onto the islands by dragging fish and algae ashore when feeding.