25 Aug 2016

Purple Sea Urchin Facts

Purple Sea Urchin Facts


Interesting Facts About Purple Sea Urchins

Purple sea urchin or Strongylocentrotus purpuratus is one good looking sea creature. You may think that it is some kind of exotic cactus after seeing its photo. To some, it may look like the flower of some unknown lily plant. The creature is most common in the eastern side of the Pacific Ocean.

One of the most striking features of this marine invertebrate is its endoskeleton like a vertebrate. The animal is nocturnal. It lives in kelp forests.

You can also learn about green sea urchins from our blog.

Habitat and Distribution

Purple sea urchins live mostly in the low inter-tidal zones. There need to be a kelp forest for them to grow and thrive. Strong waves and airflow in the water is also essential. The lives in the depth of 1 to 200 m. They prefer cold water (6-16 degree C).

North and Middle East coasts of the Atlantic Ocean are the native place of this urchin. One can found them in seas starting from Alaska to close to the Gulf of California. There are many in the Yakutat bay, Strait of Georgia, Willapa bay and nearby seas.



Purple sea urchin anatomy

Strongylocentrotus purpuratus has a round body with lots of spines. The color of the spines is purple. The animal’s test is covered with a skin. The strong endoskeleton is just under that skin.
The skeleton is made of strong plates of calcite. These plates are also become harder due to the presence of magnesium.

The spines help the creature to defend itself, though these are not poisonous. The creature’s mouth is on the underside and the anus is on the top side. There are five teeth and a strong jaw like tool named Aristotle’s lantern to cut and grind food items. For locomotion and bringing food to the mouth it uses five tube feet, special foot or hand like organs.

The tube feet rest on the test from five sides. There are also tiny pedicellariae or pincher like organs on the skin. These organs attack anything that touches its skin.



Macrocystis pyrifera
Macrocystis pyrifera

Purple sea urchins mainly feed on kelps and algae. There jaw or Aristotle’s lantern help them to scrap algae from rock and sea bottoms. There tube feet help them to grab kelp and bring it to the mouth. There most favorite kelp species is Macrocystis pyrifera.

 The Purple Sea Urchin helps to control the growth of the kelps forests under the ocean. It has very important ecological role in this regard.




Purple Sea Urchin Photo

Purple sea urchins have different male females. Both the males and females release gametes into the water where the process of fertilization takes place. The time of this process is usually January to July but in most cases it is done within the period of January to March.A small larva is developed form a fertilized egg.

Life Cycle

The larva is hatched from the fertilized egg of a Strongylocentrotus purpuratus within 24 hours of the fertilization. The larva developed into the conical echinopluteus. It becomes free floating plankton. It can remain in this stage for months. Later, it attaches itself with a hard substrate and becomes stationary. The creature’s test with spines then began to grow. It becomes sexually mature after two years. The lifespan of the animal is about 25 years.



Starfish eating Purple Sea Urchins
Starfish eating Purple Sea Urchins

Despite having a hard shell and intimidating spines, there are some predators of the purple sea urchin. Different types of sea stars like Solaster stimpsoni, Pycnopodia helianthoides, and Astrometis sertulifera loves to eat them. Their largest predator is the sea otters.


Economic Value

S. purpuratus is an edible species of sea urchin. It is a favorite of the Japanese people. They used it in their sea food “sushi”. Most of these urchins caught in the American coast are exported to Japan. It has good market value and demand there.

Strongylocentrotus purpuratus

Proliferation of Purple sea urchins is harmful for the growth of kelp forests. Too many of them can destroy the kelp forest. These kelps are valuable sources for chemicals like algin. A kelp forest is also a great source of food for the fishes. So, destruction of it can be harmful for the local economy. So, we can see that this creature has both positive and negative economic values.

purple sea urchin infographics