"Huge hawks and wild bald eagles are among some of the birds that make a meal of crabs. They pick up crabs and take them upwards, throwing them on a hard surface like a stone in order to break the crab's shell and get to the meat. Crabs have a soft shell, making them easy prey for many of their enemies.
When they're under the sea,
Sharks are natural enemies of the crab, relying on it as their only source of food.
Source: Biology Book
These characteristics can be seen in science/biology books.
In fact, all living things in nature are dependent on each other. The Creator has created this beautiful world in the shape of a circle.