Tide And Seek

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Across
  1. 3. Hard structures that form reefs (5)
  2. 5. Color of shallow tropical water (9)
  3. 6. A fast, silver fish often seen in schools (4)
Down
  1. 1. A large marine mammal known for singing (6)
  2. 2. A creature with eight arms (7)
  3. 4. The deepest part of the ocean (6)
  4. 5. The movement of ocean water caused by the moon (5)