Are Sea Urchins Poisonous Or Not?

By D.C. Demetre •  Updated: 08/12/22 •  7 min read

There are about 950 species of sea urchins, marine invertebrates belonging to the echinoderm family. They are flat or globe-shaped spiky creatures that live in shallow water, rocky areas and coral reef crannies. Urchins are related to sea creatures like starfish, sea cucumbers, and brittlestars.

It is not uncommon for people to step on them accidentally while beach-walking through shallow waves. Some people pick up the urchins to look closer, without knowing the spines need to be handled with care to avoid injury – some sea urchins release venom on contact.

Many species of sea urchins have razor-sharp spines that can puncture human skin. As you might expect, having your hand or foot pierced by a sea urchin spine can hurt. Some species, including Echinothuridae, Toxopneustes, and Tripneustes, release venom that can cause severe pain and trigger infections.

Sea urchins are not poisonous to the extent of killing a human, except for possibly one or two species.

Do Sea Urchins Sting

Are Sea Urchins Poisonous - a black sea urchin

Sea urchins are non-aggressive and relatively slow-moving animals. You won’t get intentionally stung by one. It is handling or stepping on one or accidentally brushing against one while swimming, surfing or fishing that makes an encounter with some sea urchins poisonous.

For example, black sea urchins (scientific name Diadema antillarum) have unusually long spines. Most sea urchin spines are about .40 inches to 1.2 inches long, but the spines in this species are usually 4 – 5 inches long and can grow as long as 7 inches in very large individuals.

Are black sea urchins poisonous? The spines have a slimy coating that kills any organisms trying to live in the spines. This slimy substance also contains a mild poison that helps ward off predators.

Black sea urchin spines are brittle and break into tiny fragments, making them hard to remove from a wound. Doctors will use tweezers to remove larger spines, and sharp scalpels to gently scrape out smaller spine fragments.

The venom toxins can cause temporary symptoms of itching, pain and swelling. It is usually spine fragments embedded in the skin that cause complications.

If you notice any serious symptoms such as muscle weakness, extreme fatigue, or muscle paralysis, or if you have had symptoms for more than a week, contact your healthcare provider.

Are Sea Urchins Dangerous?

The venom released by certain sea urchin species is not lethally poisonous to humans. Their spines inflict painful puncture wounds that quickly result in pain, bleeding, and swelling. They often cause severe muscle aches that can last up to 24 hours.

The venom in sea urchins is mainly for self-defence against ocean predators, including sea otters, lobsters, crabs, and wolf eels. The toxin is not strong enough to be a danger to humans.

However, sometimes pieces of spines break off and are left in the skin. In this case, symptoms can include nausea, vomiting, abdominal pain, burning or prickling sensations, low blood pressure, joint pain, granulomas, and difficulty breathing.

There is currently no anti-venom treatment available for sea urchin stings. A doctor may prescribe antibiotics and give you a tetanus shot if you need a booster. Heat breaks down sea urchin toxins, so immersion in hot water can neutralize the venom and reduce the pain.

Are Purple Sea Urchins Poisonous?

re Purple Sea Urchins poisonous

Purple Sea Urchin (Strongylocentrotus purpuratus) on a rock. Credit: Jerry Kirkhart CC-BY

 

In addition to using their spines to deter predators, some sea urchins also have small claw-shaped appendages with movable jaws, called pedicellariae. When agitated or brushed against by a potential threat, the pedicellariae will immediately snap shut and inject venom. Since these claws usually are able to release more venom than spines, sea urchin species with pedicellariae are some of the more poisonous.

The purple sea urchin (Strongylocentrotus purpuratus) is one of these. Purple sea urchins are eaten by sushi lovers, but it is the meat inside, known as “uni” in Japanese, that is considered a delicacy. It is quite safe to eat. The spines and pedicellariae are another matter. Contact with those parts of them can cause pain, swelling and infection.

The most dangerous sea urchin is the flower sea urchin (scientific name Toxopneustes pileolus). It also has pedicellariae. They are among the larger sea urchins, growing to 6-8 inches, and have short stubby spines but are covered with flower-like pedicellariae.

Flower sea urchin venom contains two or three different toxins. Their effect on humans is said to be severely painful. One biologist who accidentally got a dose of the poison, Tsutomu Fujiwara, wrote of his experience:

“I transferred the sea-urchin into a small tank in the boat. At that time, 7 or 8 pedicellariae stubbornly attached themselves to a side of the middle finger of my right hand, detached from the stalk and remained on the skin of my finger.

Instantly, I felt a severe pain resembling that caused by the cnidoblast of Coelenterata, and I felt as if the toxin were beginning to move rapidly to the blood vessel from the stung area towards my heart. After a while, I experienced a faint giddiness, difficulty of respiration, paralysis of the lips, tongue and eyelids, relaxation of muscles in the limbs, was hardly able to speak or control my facial expression, and felt almost as if I were going to die. About 15 minutes afterwards, I felt that pains gradually diminish and after about an hour they disappeared completely. But the facial paralysis like that caused by cocainization continued for about six hours.”

It is no wonder that flower urchins are considered highly dangerous. The intense, debilitating pain of their sting augmented by muscle paralysis, breathing problems, numbness, and disorientation can result in accidental drowning for divers and swimmers.

Are Sea Urchins Venomous?

A fire urchin, Asthenosoma varium

A fire urchin, (Asthenosoma varium), observed near Alor Island, Indonesia.
Credit: Candace Pratt CC-BY

 

Sea urchins are shy, nocturnal animals. They usually keep to themselves. Only a comparatively small number of the 950 sea urchin species have venom in their spines or pinchers – most are not venomous.

Certain species of sea urchins contain more venom than others. The fire urchin comes down on team venous. The fire sea urchin (Asthenosoma varium) grows up to 10 inches in diameter and lives on the Indo-Pacific ocean floor.

Its bright reddish-brown colour combines with its venom-tipped spines to ward off any potential predators. The fire urchin can deliver a painful sting to humans if handled; the resulting pain can last as long as several hours.

Are All Sea Urchins Poisonous?

Not all species are poisonous sea urchins. Some species have short stubby spines that are not sharp and contain little venom. The common sand dollar (Echinarachnius parma) is one of these sea urchins.

Around 18 species of sea urchin are edible. These sea urchins are harvested for their gonads, called the foie gras of the sea, because of the smooth texture and subtle sea flavouring.

You can also call sea urchins the porcupines of the sea. The sea urchin’s name probably derives from an Old English word (urchin, from the latin ericius) for the hedgehog, an animal similar to the porcupine.

Whether porcupine or foie gras, sea urchins are unique and fascinating creatures. Just be sure to give them the respect they are due. Handle with care and watch your step.

Sources:

  1. Craig Glenday, ed. (2014). Guinness World Records 2014. Bantam. ISBN 9780553390551
  2. Guardini, Matteo & Boyer, Massimo. Fire Urchin. World Database of Marine Species.
  3. Hendler, G., J. Miller, D. Pawson, P. Kier. 1995. Sea Stars, Sea Urchins, and Allies: Echinoderms of Florida and the Caribbean. Washington: Smithsonian Institution Press
  4. Mooi, Rich (6 May 2011). There’s just some sting about you… 2011 Philippine Biodiversity Expedition. California Academy of Sciences
  5. Puckett, E. 2002. Diadema antillarum, Animal Diversity Web. Accessed August 12, 2022
  6. Sayre, April Pulley (1996). Seashore (1st ed.). New York: Twenty-First Century Books. ISBN 0-8050-4085-4
  7. Tsutomu Fujiwara (1935). On the poisonous pedicellaria of Toxopneustes pileolus (Lamarck) Annotationes Zoologicae Japonenses. 15 (1): 62–68.
  8. Yana Gelman; Erwin L. Kong; Heather M. Murphy-Lavoie. Sea Urchin Toxicity, StatPearls Publishing; 2022 Jan