--- title: "Purple Sea Urchin (Strongylocentrotus purpuratus) | AnimalTracks.wiki" description: "A spiny kelp grazer with five teeth in a ring, whose massed feeding fronts can strip a whole kelp forest." image: "https://animaltracks.wiki/images/animals/purple-sea-urchin-1.webp" published: "2026-10-10" updated: "2026-10-10" --- # Purple Sea Urchin (*Strongylocentrotus purpuratus*) > **Status**: Checked against 6 sources, listed under Sources below. > **Tagline**: A spiny kelp grazer with five teeth in a ring, whose massed feeding fronts can strip a whole kelp forest. > **Soundtrack Vibe**: Industrial Rock & Cyberpunk // Godflesh, "Streetcleaner" > **Soundtrack Links**: [Spotify](https://open.spotify.com/track/1yhrNiagoP9JXDvUG7ahCs) > **Vibe Match**: Five teeth in a ring scrape algae off rock and dig hollows into it. Godflesh's drum machine and downtuned guitar grind in the same mechanical loop, one scrape after another. ## Biological Superpowers & Stats - **Taxonomy**: *Strongylocentrotus purpuratus* - **Danger Level**: Low - **Conservation Status**: Not Evaluated ([IUCN Red List](https://www.iucnredlist.org/)) - **Superpower**: Scrapes algae with five teeth and digs hollows in rock - **Habitat**: Rocky shores and kelp beds from Alaska to Baja California, Mexico, as deep as 160 m - **Diet**: Mostly algae, especially giant kelp, plus dead fish, barnacles and sponges - **Tags**: invertebrate, benthic, tide-pool, regeneration ## Natural History & Behavior ## A pincushion with a chisel for a mouth The purple sea urchin is a round, spiny animal. Its body shell is called a test, and it can grow up to 10 cm (4 in) across. California Sea Grant gives a typical size of 5 to 10 cm wide and 4 cm tall. Young urchins are mostly pale green, and their spines darken to purple as they mature. Its mouth sits underneath. It holds five sharp teeth arranged in a circle, a set called Aristotle's lantern. The urchin scrapes algae off rock with them. It can also use them to dig a hollow in rock for protection. Sometimes an urchin grows too big to leave its hollow and is stuck there. Pincers on long stalks, called pedicellariae, help it defend itself from attackers and keep barnacles and sponges from settling on its body. ## From Alaska to Baja *Strongylocentrotus purpuratus* lives along the Pacific coast from Alaska to Baja California, Mexico. It likes rocky shores and kelp beds, from the intertidal zone as deep as 160 m (525 ft). Kelp is its favourite food. It will also eat dead fish, barnacles and sponges. Warm water is a problem. At temperatures above 22.8°C (73°F), more of them die. > **Urchin barrens** > Purple urchins have two feeding modes. When drifting kelp is plentiful, they sit and catch it. When the supply drops, they switch to active foraging and form dense feeding fronts that can remove a kelp forest completely. What is left is called an urchin barren. Once the food is gone, the urchins' gonads shrink, and they can linger in this "zombie" state for decades. Sea otters and sunflower stars eat urchins, and fewer of both have let urchin numbers jump. California Sea Grant reports that some areas, such as northern California, have enough urchins to suppress kelp. ## A very long life The Oregon Coast Aquarium gives an average lifespan of 20 years and says some may live as long as 70. A 2016 aging study, citing earlier work, puts the maximum life expectancy in the wild at more than 50 years. In that study, old urchins regrew snipped-off spines and tube feet as quickly as young ones. Tube feet help the urchin move, breathe and sense its surroundings. ## A lab favourite Scientists sequenced this urchin's genome in 2006. It holds more than 814 million letters of DNA and 23,300 genes. The urchin and humans share an ancestor that lived over 540 million years ago. The head of the US genome institute said then that urchins share substantially more genes and biological pathways with humans than expected. ## Frequently Asked Questions ### Why does a purple sea urchin cover itself in shells and bits of seaweed? At low tide, when the water has pulled back, it sticks pieces of shell, rock and algae onto itself. The Aquarium of the Pacific says this protects and camouflages it. *(Source: [Aquarium of the Pacific]())* ### What eats purple sea urchins? Besides sea otters and sunflower stars, the Oregon Coast Aquarium lists leather stars, California sheepshead and spiny lobsters as main predators. *(Source: [Oregon Coast Aquarium]())* ### Do people eat purple sea urchins? Yes, the egg or sperm organs (gonads) are the part eaten. California harvested the species for food in the 1990s, but the catch is now mostly harvested for scientific research. *(Source: [California Sea Grant, California Seafood Profiles]())* ## Sources 1. [Purple Sea Urchin. Aquarium of the Pacific.]() 2. [Purple Urchin. Oregon Coast Aquarium.]() 3. [Purple Sea Urchin. California Sea Grant, California Seafood Profiles.]() 4. [Strongylocentrotus purpuratus. SeaLifeBase.]() 5. [California Purple Sea Urchin Genome Sequenced by International Team. Caltech.]() 6. [Bodnar & Coffman (2016). Maintenance of somatic tissue regeneration with age in short‐ and long‐lived species of sea urchins. Aging Cell.]() *Published October 10, 2026. 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