The easiest way to win this fight is to use a sac-pull method to only pull the Boss monsters, ignoring and de-aggroing the weaker monsters. Monsters have Alliance hate only, so make sure the pullers are outside the alliance before beginning.
Only the boss needs to be defeated in order to win. Doing so will instantly kill all other monsters.
Damask Crabs are resistant to physical damage.
Cyanic Crabs are resistant to magical damage.
Killing the crabs cause more to repop from the starting area.
Upon killing crabs, occasionally the boss Caldera Crab will come to its aid, running to where the crab was killed.