Red Rock Crab

Description:

Large red crab about the size of my hand eating out of a mussel shell.

Habitat:

Spotted during low tide at La Jolla Shores on a small island covered in barnacles and surrounded by water

Notes:

I believe the creature on top of the crab is a Red-Striped Acorn Barnacle: http://nathistoc.bio.uci.edu/crustacea/C... The two organisms share a symbiotic relationship because when the crab moves, the mussel can filter feed therefore get the food it needs to survive. The crab gets protection from predators because organisms riding on it help it camouflage with it's surroundings. The Red Rock Crab is known to crush barnacles with its large pincers to eat. This is parasitism when the crab eats the barnacle. The barnacle gets no benefit from this relationship but the crab does so it's parasitism.