“Endangered underwater ecosystem” crossword clue

Reveal the answer to see why it works and where this clue has appeared before.REEF is the answer to the New York Times crossword clue “Endangered underwater ecosystem”. It was last seen in the puzzle of September 29, 2025, where it runs at 60 Down and fills 4 squares. It crosses 4 other entries in that grid — those are listed below and are the quickest way to confirm the letters you already have.