The dead limpet (blue) and the hermit crab (purple). I couldn't tell if the shell on the dead limpet was another crab or just a sea snail. There were other hermit crabs nearby though so I'm thinking a crab.
I was really excited by this development, so I called the others over to have a look (and lend me a phone to take pictures!). The water was freezing but I scooped him up to have a closer look for a second or two. As I expected, he went full-defensive mode and retreated inside his borrowed shell, waving his cute little claws menacingly at me through the opening. I didn't want to disturb him too much though so I popped him back down right where I got him from. He spent thirty seconds or so peering up at me suspiciously, but when he was satisfied that I wouldn't pick him up again he went straight back to chomping limpet.
"Put me down, mammal! I've got a busy day ahead!"
The tide was slowly making its way towards us so we went back up onto the promenade, but it was great to see nature happening right on my doorstep! I love how pretty much anywhere you look in the world, you will find little ecosystems full of fascinating organisms!