Food chains.
Florescent Perspex, 130mm x 130mm x …and growing!
.
Antarctic clams eat diatoms.
Penguins ingest clam shells to strengthen the shells of their own eggs.
New research led by a University of Washington biologist (Professor Dee Boersma) shows that during the period when eggs are being laid, female penguins have significantly more mollusk shells, mainly clams and mussels, in their stomachs than males do. The mollusk shells gradually leach calcium used to form eggshells.
(my italics)
Science Daily May 11, 2004