Many animals winter hibernate. Why do sea cucumbers summer hibernate?

Sea cucumbers are echinoderms that dwell in the mud and sand at the bottom of the ocean, from the deep sea to shallow waters. They can be found all along the coast of China. Sea cucumbers have long, slender bodies with thick, fleshy walls. They are covered with many fleshy protrusions on the outside, making them resemble fresh cucumbers, hence the name “sea cucumber.”

Sea cucumbers do not have distinct heads or tails. At the center of the anterior end of their bodies, there is a small hole that serves as their mouth. Surrounding the mouth is a ring of cylindrical, jasmine-like tentacles used for catching food.

Many animals hibernate by retreating into tree holes, underground burrows, or rock crevices when food sources are scarce. For example, yellow-bellied marmots and groundhogs, which primarily feed on green plant parts; hedgehogs, which rely mainly on wetland worms and insects; and even large bears that eat certain plants, all hibernate due to insufficient food.

However, sea cucumbers “aestivate” in the food-rich summer. Why is this?

Sea cucumbers feed on small organisms. When there is an abundance of these organisms on the sea floor, sea cucumbers feast and live contentedly.

However, the organisms on the sea floor also change with the temperature of the seawater. These organisms are very sensitive to changes in water temperature. When the surface water is warm, they rise to the surface; when the water cools at night, they return to the sea floor. This rise and fall pattern is the daily habit of small marine organisms.

In the summer, the surface water temperature becomes relatively high due to the intense sunlight. Consequently, the small organisms on the sea floor float to the surface to engage in their annual breeding. During this time, the sea cucumbers, which cannot move or chase after them, are left behind on the sea floor with no food. To cope with this period of starvation, they have no choice but to “sleep.” Just as animals hibernate in winter due to a lack of food, sea cucumbers can aestivate in summer when food is scarce.