Has potential.
Add some more elements to it;
-increase enemies, ones that do various 'attacks'
-different ways to get the pearls, like opening clams, or killing fish that swallow the pearls (just suggestions not that this has to be done)
-maybe add some mini-challenges like the most pearls grabbed in a single dive, or timetrials (quickest time getting X amount of pearls, or least trips to the boat etc..)