A lot of coral whistle-blower covers close to shore (4)
I believe the answer is:
reef
'a lot of coral' is the definition.
I can't judge whether this defines the answer.
'whistle-blower covers close to shore' is the wordplay.
'whistle blower' becomes 'ref' (a referee blows a whistle).
'covers' indicates putting letters inside.
'close to' suggests the final letters (the 'close' to the word).
The final letter of 'shore' is 'e'.
'ref' enclosing 'e' is 'REEF'.
Can you help me to learn more?
(Other definitions for reef that I've seen before include "Coral outcrop" , "Ridge of coral near the sea surface" , "The Great Barrier ..., Australian natural wonder" , "Shoal; take in (sail)" , "Ridge of rock just under water" .)