Mussels and oysters you can sometimes just pick up at low tide. They are eaten raw. But to avoid bacteria, you can better heat them quite enough. They then open automatically.
The bacteria in a moist environment reduce sustainability. Therefore, it was, before there were refrigerated transports, recommended to eat mussels only in the cooler months with R.
In the spring months mussels shoot seed and they are less suitable for consumption. From mid-April to mid-July, we speak of the quiet season.
The almost risk- free picking of molluscs (mussels and others) by generations of hunters - gatherers from Canada to Tierra del Fuego, and from Spain to Scandinavia, ensured meters thick layers of empty shells along shores. Later often reused in lime production.
If you get to see crab or lobster, you can grab them from behind, or at least behind the crowds. If you have a mask you can find them in crevices and caves.
Crabs often move sideways, lobsters and shrimps swimming very rapidly backwards. Watch out for the claws, they are cracking shells and fingers. You can also catch them in fykes and traps with bait.