Sea Cucumbers’ Incredible Defense Mechanisms

Sea cucumbers may seem defenseless, but they’re actually pretty tough animals. Since they’re relatively slow animals and can’t attack or escape their predators, they have developed other defense mechanisms that can efficiently scare off or even kill other animals. If you wonder what exactly sea cucumbers can do to defend themselves, I’ll talk about that in this article. But, let’s begin with a quick answer:

When threatened, sea cucumbers expel internal organs through their anus that can immobilize or even kill their predators. Another defense mechanism is that they can liquefy their bodies and escape through narrow spaces. Sea cucumbers can also clone themselves or swim away when predators are nearby.

However, this certainly doesn’t tell the whole story. Below I’ll explain more about each of the sea cucumer’s defense mechanism and I’ll talk about sea cucumbers’ predators. Read on!

How do sea cucumbers defend themselves? (Explained)

Sea cucumbers, just like all other animals, are not defenseless. They’ve adapted to their environment and developed many defense mechanisms to survive. Some of them are unique and make these marine creatures incredibly fascinating. Below you can find a description of five ways how sea cucumbers prevent from being eaten.

Expelling internal organs

Sea Cucumber Expelling Organs

One of the sea cucumbers’ fascinating defense mechanisms are their long white slender tubules, called Cuvieran tubules. When the animal is disturbed, it ejects the sticky tubules through its anus or some through the mouth. Scientists have debated this underwater superglue’s function for over a century.

Although the Cuvieran tubules are capable and have been observed to catch crabs in the laboratory, there is still a lack of field evidence to support this theory. The most common conclusion is that this sudden ejection may act as diversion or a repellent to predators.

Expelling tubules involves the loss of the gut, the water vascular system, and the haemal system. This sounds like a very problematic event for the lifespan of sea cucumbers, but this is where these animals become fascinating. They can grow their organs back within a few weeks!

Interestingly, some species may release toxins together with tubules. These toxins are called holothurin and can be deadly to many marine animals. Moreover, they’re also poisonous to humans, and if they come into contact with the eyes, they may even cause permanent blindness.

Liquefying the body

Another sea cucumbers’ extraordinary ability is that they can transform themselves into different states of matter. When these animals need to escape, they can pass through narrow spaces by liquefying their bodies and returning to a solid form again. It’s possible thanks to their unique collagen fibers in the tissues.

This special power of sea cucumbers is a revolutionary discovery. Scientists have been studied the remarkable properties of the sea cucumber’s tissues to fully understand it and use it within the realm of human application.

Cloning itself

Some sea cucumber species have the ability to clone themselves in response to the presence of predators. This process usually occurs in the larval stage when sea cucumbers haven’t developed other defense mechanisms. This form of reproduction also occurs in closely related sea stars or sand dollars.

Cloning is accomplished by fragmentation and involves dividing the body into two or more parts. Thanks to this event, sea cucumbers are a less obvious target as the copied larva is usually about half the size of the original one.

Swimming away

Surprisingly, some sea cucumbers can swim when they feel threatened. The swimming movement is usually created by lifting their bodies off the seafloor and rapidly flexing it. For instance, the shallow-water California sea cucumber (Apostichopus californicus) lifts off the surface and swims away with undulating movement when touched by the arm of the predatory sea star.

Some species use swimming as a primary way of locomotion. These sea cucumbers look different as their bodies have morphological adaptations for swimming. You can read more about it in my other article: “How Do Sea Cucumbers Move?”.


The large size of some sea cucumber species is also effective protection against predators. They can’t be consumed whole and they can rely on their amour, spines, and toxins to stop attempts to remove pieces of their body. When they’re juveniles, they hide most of their time under rocks or any tight slots.

What are the predators of sea cucumbers?

You might now think, what animals actually eat these creatures? There are a few that hunt sea cucumbers, such as sea stars or snails. Starfish eat sea cucumbers by extending their stomach out of their bodies and digesting food directly. After the dinner is finished, it pulls its stomach back in. This way, sea stars can eat animals that are much bigger than themselves.

However, snails have a different strategy. They apply the toxins first to subdue a victim and suck the food in with their large proboscis. Maybe you wouldn’t expect it from a snail, but they can swallow the whole sea cucumber, just like a Python.

Other predators of sea cucumbers are crabs, lobsters, some fish species, turtles, sharks, sea otters, seagulls, seals, walrus, and humans. You can read more about it in my other article, “Top 10 Predators Of Sea Cucumbers”.

Are sea cucumbers dangerous to humans?

Sea cucumbers, at first glance, are harmless to us. They don’t have sharp teeth that they could bite us with and no strength to harm us. However, as I previously mentioned, they can expel toxins when they feel threatened. Holothurin toxin is a strong poison that quickly weakens the enemy muscles or kills them.

It shouldn’t harm us when we touch it, but it can cause a skin rash in some people. When contact with the eyes, it can cause permanent blindness. This is partially a risk for a diver who clears a mask in the area where a sea cucumber was recently manipulated.

If you experience irritation from the sea cucumbers’ toxins, you should rinse the affected area with seawater. Don’t wash it with fresh water as it can increase pain. If your eyes were exposed, rinse them with 1 to 2 gallons of fresh water or saline solution immediately.

Next, you can follow by immersing the wound in warm water and applying the acetic acid. You should seek medical care immediately if your eyes are exposed.


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