Since they were in the ocean (I assume that is the beach you are refering to), put them in a bucket with boiling water (or boil them in a pot on the stove), let them boil for 5-10 mins. Let the water cool, then put some aquarium salt on a plate. wet a scrub brush in the boiled water and dip it on the plate to pick up some salt and start scrubbing.. Rinse when done.
Beautiful place out there, sadly aside from the ferry ride out to the island I didn't get to see much of the ocean..