From beginner to expert:
  1. A piece of the Great Pacific Garbage Patch
  2. Plankton
  3. Nudibranch
  4. Puffer fish
  5. Crappie fathead
  6. Smelt
  7. Giant squid
  8. Flying fish
  9. Sailfish
  10. Tsunami
  11. Supersonic submarine
  12. Aquaman
    Or the gender-neutral equivalent
  13. Poseidon
  14. Flotsam / jetsam
    Suggested by @evan