A young gull ineffectually rummaging in seaweed, then pestering an adult (presumably mum), who firstly backed off, then gave it a marine snail, followed by something regurgitated, then found some bivalves which she dropped from a height on a concrete slipway & left for the youngster. She didn't check to see if they'd cracked open, but the young one obviously recognised the action & went for 'em.