Ecosystem set Carol free (5,4)

I believe the answer is:

coral reef

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'ecosystem' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.

'set carol free' is the wordplay.
'set' is an anagram indicator (instruction to set the letters).
'carol'+'free'='carolfree'
'carolfree' with letters rearranged gives 'CORAL-REEF'.

Can you help me to learn more?

(Another definition for coral reef that I've seen is " Navigational hazard in warm seas - real force (anag)".)

I've seen this clue in The Daily Express.

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