Stopped talking, observing seafood presented to first person at party in Northern Ireland (7,2)
I believe the answer is:
clammed up
'stopped talking' is the definition.
I can't judge whether this defines the answer.
'seafood presented to first person at party in northern ireland' is the wordplay.
'seafood' becomes 'clam' (clam is a kind of seafood).
'presented to' means one lot of letters go next to another.
'first person' becomes 'me' (first-person pronoun).
'at' is a charade indicator (letters next to each other).
'party in northern ireland' becomes 'DUP' (Democratic Unionist Party).
'clam'+'me'+'dup'='CLAMMED UP'
'observing' is the link.
Can you help me to learn more?
(Other definitions for clammed up that I've seen before include "made no comment" , "Informally, stopped talking like bivalve" .)