Evidence and details from the text
The phrase idiom is a phrase<span> or a fixed </span>expression<span> that has a figurative, or sometimes literal, </span>meaning.
Explanation:
1) Coral reefs are underwater ecosystems which are formed of colonies of Coral Polyps, a Famous and well-known Coral Reef is the Great Barrier Reef, which is located off the coast of Queensland, Australia.
2) A couple of threats to the world's oceans include, Plastic Pollution, Global Warming and Acidification.
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