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Pacific Purple Sea Urchin

Known for its striking purple color, this urchin plays a vital role in maintaining the balance of kelp forest ecosystems. In healthy numbers, they help control algal growth, but when populations boom unchecked, they can devastate kelp forests.

 

Found along the Pacific coastline from Alaska down to Cedros Island, Mexico, the Pacific purple sea urchin thrives in intertidal zones with strong wave action where water is always in motion. It has a round body with a radially symmetrical shell, covered in large spines. While difficult to see, it also has a mouth, which usually faces down, and tube feet that they can use to move. This urchin can live by itself or come together in groups with others when a good food source is available. It primarily feeds on algae — snatching pieces out of the water with its tube feet and spines or scraping it off rocks using its bony teeth and strong jaws.

However, the Pacific purple sea urchin’s favorite food – and the one that brings individuals together to feed — is giant kelp. They are known for their aggressive feeding behavior, and population explosions are believed to be at least partially to blame for the decline of kelp forests in Northern California. This — along with marine heatwaves that decimate kelp forests — has led to the increase of “urchin barrens” or large swaths of seafloor overrun by this urchin as well as other species. Predators like sea otters which prey on these urchins and others are key in regulating sea urchin populations and preventing overgrazing.

 

 

In recent years, the Pacific purple sea urchin population has been exploding — which poses a significant threat to the kelp forests where they live. It is also a problem for the urchins themselves, since overgrazing on bull kelp in turn leaves nothing left to eat and the urchins to starve. While it may seem counterintuitive, efforts to harvest more sea urchins for food or other purposes help to restore kelp forests and let the entire ecosystem thrive.

 

 

Oceana works to safeguard ocean habitat, including coastal habitat, that they and so many other creatures call home. Our campaigns along the United States’ Pacific Coast help gather important information about the forests here so that we know best how to protect them. Learn more about our work here.

 

 

 

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