Big beasts manage a half-full swamp (9)

I believe the answer is:

megafauna

I'm a little stuck... Click here to teach me more about this clue!

'manage a half-full swamp' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'big beasts' is the wordplay.
'big' becomes 'mega' (I've seen this before).
'beasts' becomes 'fauna' (I've seen this in another clue).
'mega'+'fauna'='MEGAFAUNA'

Can you help me to learn more?

(Another definition for megafauna that I've seen is " Large animals of a region".)

I've seen this clue in the Sydney Morning Herald.

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