海 (うみ, umi) – sea; ocean; waters

海面 (かいめん, kaimen) – sea level; (surface of) sea

海洋底 (かいようてい, kaiyoutei) – ocean floor; sea floor; seabed

藻場 (もば, moba) – seaweed bed; seaweed forest

魚 (さかな, sakana) – fish

鮫 (さめ, same) – shark

海がめ (うみがめ) – sea turtle

珊瑚 (さんご, sango) – coral

海老 (えび, ebi) – prawn; shrimp; lobster; crayfish

海星 (ひとで, hitode) – starfish; sea star; asteroid; any echinoderm of the class Asteroidea

Definitions from jisho.org.