Taken before lunch, stuff including black seafood (8)

'seafood' is the definition.
(crabmeat is a kind of seafood)

'taken before lunch stuff including black' is the wordplay.
'taken before' says to put letters next to each other.
'lunch' becomes 'eat lunch' (to lunch can mean to eat lunch).
'stuff' becomes 'cram' (cramming is a kind of stuffing).
'including' means one lot of letters goes inside another.
'black' becomes 'b' (as in pencil classifications).
'cram' enclosing 'b' is 'crabm'.
'eat' after 'crabm' is 'CRABMEAT'.