I found this at the opening of an estuary on Vancouver Island. There were hundreds of crabs visible on rocks just under the surface of the water. This crab was the largest I saw. I noticed what I thought at first was algae growing on its claws. I found though that the fleshy growth was attached to the crab; and there was an identical one on each claw. The claws seemed to be shaped so these fleshy green-brown lumps may have been coming out from a bulge in the claw.