Lugworms.

A low spring tide, so the fishermen were out in force digging for...Lugworms, Arenicola marina. These polychaetes live in a u shaped burrow in the sand and filter food particles out of the sediment. They can make up a third of the biomass of a sandy beach.
Humans having dug holes and left piles of sand around, some oystercatchers came and had a scavenge.