there are beaches....

...and there are beaches and very few of them are literally metres deep in shells.
Welcome to Shell Beach and the magnificent mollusc that crunches underfoot is 'Cardiid' a small edible cockle.
Here also known as the Hamelin, Heart or Fragum  Cockle it is found only in these very salty (hypersaline) waters of Shark Bay.
Unlike your average cockle that filter feeds plankton these dudes have adapted to the super salty environment and a single cell photosynthetic algae has taken up residence in the cockle photosynthesizing food  and capturing  calcium carbonate for its shell.

Cockling Clever!!