Poems and essay, say, on Black Sea port (6)
I believe the answer is:
odessa
'black sea port' is the definition.
(Ukrainian port on the Black Sea)
'poems and essay say' is the wordplay.
'poems' becomes 'odes' (ode is a kind of poem).
'and' means one lot of letters go next to another.
'say' shows a homophone (sound like).
'essay' is a homophone of 'sa'.
'odes'+'sa'='ODESSA'
'on' acts as a link.
(Other definitions for odessa that I've seen before include "Black Sea location" , "Do seas come into Ukrainian city?" , "Ukrainian naval base" , "Port city of Ukraine" , "Ukrainian location" .)