Pacific Purple Sea Urchin | Oceana

Corals and Other Invertebrates

Pacific Purple Sea Urchin

Strongylocentrotus purpuratus

Pacific Purple Sea Urchin

Distribution

Pacific Coastline from Alaska to Cedros Island, Mexico

Ecosystem/Habitat

Low Intertidal Zone

Feeding Habits

Foraging Omnivore

Taxonomy

Phylum Echinodermata, Class Echinoidea (spiny, globular animals)

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Pacific purple sea urchins are easily identifiable on the ocean floor because of their distinctive purple color. They are covered in pincers, tube feet, and purple spines that move via ball-and-socket joints, using these spines to grab food and protect themselves from predators.

Urchins on the Pacific seafloor, including purple sea urchins, are important prey for sea otters and sea stars. Pacific purple sea urchins are also eaten by humans. The meat inside, known as “uni” in Japanese,2 is considered a sushi delicacy, and the demand for this delicacy has been growing in recent years.  

Pacific purple sea urchins feed on kelp and are at least partially to blame for the deforestation of Northern California’s kelp forests due to their increasingly aggressive feeding behavior.1 Marine heatwaves have caused kelp forests declines, and helped give rise to what is known as increasing “urchin barrens,” or large swaths of seafloor that are overrun by kelp-feasting Pacific purple sea urchins and other species. This population explosion can also be credited to a climate change related sea star die-off in California waters, which otherwise would have helped keep the sea urchin population in check.1 The historical hunting of sea otters that prey on sea urchins for the fur trade also contributed to the urchin population increase.

Intense ocean warming and the strain of sea urchins aggressively preying on kelp has led some researchers to fear that continued, unchecked kelp deforestation from the Oregon coast to Monterey Bay, California may lead to a total collapse of the delicate ecosystem created by kelp forests, putting countless species at risk.4

Researchers suggest that one way to help save kelp forests is for humans to eat more sea urchins.5 Oceana campaigns to restore the world’s oceans in order to increase biodiversity and deliver more seafood for the future. A healthy ocean could feed 1 billion people a healthy seafood meal each day. Join Oceana to help save the oceans and feed the world.

 

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Fun Facts About Pacific Purple Sea Urchins

1. The pin cushion appearance extends from a round inner shell, called a “test."

2. The toothlike plates that surround an urchin’s mouth are called “Aristotle’s lantern.”

3. Though commonly referred to as roe, as in the eggs of a sea creature, uni sushi is actually the animal’s gonads.5

4. Sea urchins can walk, using their tube feet to move along the seafloor. These feet are also how the sea urchin breathes.

5. Sea urchin grazing is slowly but steadily decimating kelp forests on the U.S. West Coast.1

 
 

Engage Youth with Sailors for the Sea

Oceana joined forces with Sailors for the Sea, an ocean conservation organization dedicated to educating and engaging the world’s boating community. Sailors for the Sea developed the KELP (Kids Environmental Lesson Plans) program to create the next generation of ocean stewards. Click here or below to download hands-on marine science activities for kids.

 

Kids Environmental Lesson Plans

 

 

Additional Resources:

1. Scientific Reports

2. Science Friday

3. Animal Diversity Web

4. Research Gate

5. Smithsonian

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