Really nice, Rob, but what are they?

In fact not from excavation of burrow as I thought. The balls of sand are left after the crab has sifted any tiny food particles from the sand, feeding on the surface. A search for "crab sand balls" should get you some YouTube links.

I've found some video and many photos.Very nice and interesting :-)

Ciao Rob, una bella foto ed interessante, adesso che ho visto i vostri commenti con Daniela farò una ricerca anch'io ciao buon WE, con amicizia bruno