Sea cucumbers are marine invertebrates belonging to the class Holothuroidea, part of the phylum Echinodermata. These soft-bodied animals primarily inhabit the seafloor across all oceans. As detritivores and suspension feeders, sea cucumbers play a significant role in marine ecosystems, serving as both decomposers and, at times, prey.
Marine Predators
Several marine animals prey on sea cucumbers. Common predators include certain fish species, crustaceans like crabs and lobsters, and other echinoderms such as starfish. The specific predators can vary depending on the sea cucumber’s habitat and species.
Fish species like triggerfish and pufferfish feed on sea cucumbers. Some larger fish, such as tuna, cod, and sunfish, also consume them. Sharks can also prey on sea cucumbers, though they are not typically a primary food source.
Crabs and lobsters are significant crustacean predators, using their claws to break apart or handle sea cucumbers. Lobsters frequently include echinoderms in their diet. Sea stars are also predators of sea cucumbers, despite being closely related within the echinoderm phylum. The sunflower starfish, a large species from the Northeast Pacific, consumes sea cucumbers by extending its stomach over the prey and digesting it externally.
Certain sea snails, such as the giant Partridge Tun snail, specialize in preying on sea cucumbers. These snails can subdue their victims with powerful venom before swallowing them whole using a large proboscis. Marine mammals like sea otters and walruses, which primarily feed on invertebrates, include sea cucumbers in their diet.
Unique Defenses
Sea cucumbers have evolved a range of defense mechanisms to protect themselves from predators. One is evisceration, where the animal expels internal organs, such as parts of its gut or respiratory trees, through its anus when threatened. This act serves to distract or entangle the predator, allowing the sea cucumber to escape. Despite losing vital organs, sea cucumbers can regenerate these lost parts, typically within days or weeks.
Many species can eject sticky, thread-like Cuvierian tubules from their anus. These tubules, which are extensions of the respiratory tree, rapidly expand and become highly adhesive upon contact with seawater. They can entangle and immobilize predators like fish and crabs. The Cuvierian tubules can also be regenerated.
Beyond physical defenses, many sea cucumbers employ chemical deterrents. They produce toxic compounds known as saponins. These chemicals, concentrated in the body wall and especially in the Cuvierian tubules, make the sea cucumber distasteful or even toxic to many predators. The presence of these toxins can deter a wide array of marine animals from consuming them.