As it happens, adult American lobsters have few predators other than man. They're big, well-armored, have immensely powerful claws and live in deep burrows. Juvenile lobsters are vulnerable to ground fish, but an adult lobster is only likely to be eaten by brave seals and humans.
True enough, for now. It seems climate change has created a lobster population boom, though (they love the warmer water), so I would say it's only a matter of time before evolution takes notice of this "free lunch" and adapts some of the neighbouring predators to better get at them.
