This is a double puzzle: first, you've got to figure out the kenning (2 words); then you've got to interpret what the kenning means (1 word noun). An example of a kenning is bookworm for voracious reader or rug rat for infant who can't walk yet. For more info, look at this answer of mine. Clue: the final answer is a beach/sea creature.
clam/shell cracker -> otter? I think otters are known for cracking shellfish open?
The answer I was thinking of is