Who's at sea with a single source of nutrition? (7)
I believe the answer is:
abalone
'who's' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'sea with a single source of nutrition?' is the wordplay.
I cannot really see how this works, but
'a' could be 'one' and 'one' is present in the answer.
'single' could be 'a' and 'a' is present in the answer.
This explanation may well be incorrect...
'at' is the link.
Can you help me to learn more?
(Other definitions for abalone that I've seen before include "produces an ear shell" , "sea mollusc" , "Mollusc also called ormer" , "Ormer, ear shell" , "shellfish for instance" .)