If the game freezes, just click inside it (games can get unresponsive if you click elsewhere on the page).
Even more valuable than the shells themselves is the ocean adventure!
Dive to the bottom with the Arrows and collect as many shells as you can before running out of air. When you reach the surface, your shells will be counted and your air will fill up for another dive. Collect trash for bonus points, and don't touch the dangerous animals or you will lose all your shells.