How To Tell If Sea Urchin Dead? And How They Lose Their Spines?

While hunting for shells you might come across a sea urchin on the beach, or even have one at home as an interesting pet. Sea urchins are fascinating creatures, but due to their unique appearance, many people find it hard to tell if it’s alive or dead. 

There are simple things to look for, such as the state of its characteristic spikes, which can help determine whether it is still living. Here is a comprehensive guide to help you understand sea urchins and make sure that you aren’t mistaken when you say that one is dead. 

What are Sea Urchins? 

Before we can dive into understanding what a sea urchin is like when it’s dead, it is a good idea to evaluate exactly what a sea urchin is when it’s alive. 

Sea urchins, scientifically known as Echinoidea, are shiny, spherical creatures that inhabit the seas and oceans. They are known particularly for the long, thin spines (also called celia) that cover their bodies such as porcupine needles. These spines help protect them from nearby predators.

Sea urchins don’t have what can be called an ‘eye’ in the traditional sense. Their entire body is a compound eye which helps them navigate using information from surrounding light intensities. 

Sea Urchin Eating Habits, and Habitat

Sea urchins are herbivores who thrive on algae, barnacles, and other small slow-moving creatures. It is interesting to note in places like coral reefs, sea urchins are vital in helping prevent the overpopulation of algae. Sea urchins can be found in both hot and cold saltwater bodies, in a range of different depths. 

Identifying a Dead Sea Urchin

Due to their unusual appearance, it is often hard for people to tell if a sea urchin is dead or alive. One of the simplest things to notice about a dead sea urchin is that its spikes have fallen off. It is also interesting to note that bald sea urchins are usually empty from the inside which is another sign that they are dead. 

Any sea urchin that has some of its spines still attached has a high chance of being alive. If you spy such a sea urchin on the beach, it is a good idea to use a shovel to gently scoop it up and put it back in the water. 

How do Sea Urchins Lose their Spines? 

Despite their spines, sea urchins are very sensitive to their external environment. Here are some of the changes which may cause them to lose their spines. 

  • Lack of Salt in Water: if you have a sea urchin as a pet, make sure there is enough salinity in the water as sea urchins cannot survive in freshwater conditions. 
  • Osmotic Shock: sea urchins that have been kept in tanks need to have the tank water cleaned and changed regularly. If you are only “topping off” the water, there will be an accumulation of pollutants that might affect the pH levels of the tank
  • pH Instability: Since these creatures can only survive in conditions where the pH value is between six and nine, a change in pH would cause their spines to fall off. 
  • Lack of Food: starvation is one of the main causes a sea urchin to lose its spines. If the surrounding environment has a low amount of algae, or any small organisms that are fit for sea urchins to eat, chances are that it will lose its spines due to starvation. 

How do Sea Urchins Die? 

Like for all living creatures on this planet, many reasons can cause a sea urchin’s death. Here are some factors that can affect sea urchin mortality.

  • Predators: it can’t be ignored how predators play a big role in affecting sea urchin populations. Large populations of marine creatures like shellfish that include crabs, and lobsters, to sea otters are equipped to preying on sea urchins. Other predators include eels and fish like wrasse and triggerfish. 
  • Prolonged Exposure to Unfit Environment: as mentioned previously, sea urchins thrive under specific environmental conditions. If the pH levels or even the level of salinity in a water body are affected, it may cause most sea urchins to die. Moreover, water that contains a large number of pollutants can also affect sea urchin health and reduce its lifespan. 
  • Development of Disease: Some diseases like Bald Sea Urchin disease often spread across sea urchin populations and cause the sea creature’s spines to fall off. This premature “balding” makes it harder for them to keep predators away, making them easy prey. 

How Long Do Sea Urchins Live For?

If you have a pet sea urchin or a general interest in unusual sea creatures, you may be wondering how long sea urchins typically live. It may come as a surprise to find that sea urchins have a long life span that ranges from 15 to 200 years! The rare red sea urchin is considered to be amongst the oldest living creatures on earth! 

The lifespan of these unique sea creatures can be on the high side if they are in good health and ideal environmental conditions. 

Is a Dead Sea-Urchin able to Sting? 

Some people are shocked to find that a dead sea urchin is still able to sting. The stinging occurs as a result of two poisonous organs namely its pedicellaria and the protruding spines. The sharp spines often form puncture wounds on the exposed flesh. 

The sting of a sea urchin is serious as it can trigger an inflammatory reaction in the body. This reaction can cause a variety of serious medical issues such as tissue necrosis, respiratory failure, paralysis, and may even prove fatal. 


Knowing how to tell if a sea urchin is dead is important for your safety and that of people around you as even dead sea urchins are known to sting. A sea urchin can be identified as dead as it is usually hollow from the inside.

Moreover, it can be distinguished from a living sea urchin as its spines are falling off, making it look as if it is balding. Hope this helps!