Instructions
Enter Coral Cave and walk to the back of it, where a large pirate galleon has sunk.
Activate the switch and use the bridge to access the ship.
Avoid the jellyfish in the first room. Jump the exposed divide to the back half of the ship, then drop into the hole in the deck to initiate a "boss battle," which is generally a fight with a more difficult opponent.
Attack the crystal that activates, fleeing a short distance after each strike to avoid its counterattack. Once it the crystal is dispatched, collect the blue pearl that it relinquishes.