The pearls can be collected when an oyster opens itself and exposes a pearl. Just swim close to the oyster to collect the pearl. If you get close to the sea creatures then it will be game over. So be careful, also keep an eye on your breathing meter at the top. If you run out of breath you will die, so periodically swim up to the surface and fill your lungs with air before setting out for more pearls.
Use the Arrow Keys to swim around in the water. Enjoy your dive!