Purple Sea Urchin

• Its genome was fully sequenced in 2006, revealing a surprising evolutionary closeness to the vertebrates.
• It feeds mainly on kelp, supplemented with dead fish, barnacles and sponges.
• It lives in the low intertidal and rocky subtidal of the eastern Pacific, in kelp forests.
• It is the protagonist of the Pacific's urchin barrens. When its predators disappeared — above all the sunflower sea star, devastated by wasting syndrome since 2013 — its populations exploded and stripped the kelp forests of the North American west coast.
• And they endure: in an urchin barren, with hardly any food, they enter a dormant state with empty gonads and can survive for years lying in wait, which prevents the forest from recovering on its own.
• It carves out its own hollow in the rock, wearing it away with its teeth and spines, and many individuals end up trapped in their own pit.
• It lives up to fifty years or more, and is one of the classic model species of developmental biology: its transparent, externally fertilised embryo was key to understanding fertilisation and the first cell divisions.
• Its genome was sequenced in 2006, one of the first for a marine invertebrate.
• Its gonads are the uni of Japanese gastronomy, and its commercial fishery has grown precisely by taking advantage of the population explosions.

Skeleton type

Invertebrate - endoskeleton of calcareous plates (echinoderm)

Habitat and environment

Low intertidal and rocky subtidal zones of the eastern Pacific, from Alaska to Baja California, in kelp forests

Birth weight

A microscopic pluteus larva after external fertilisation

Size at birth

Microscopic larva after fertilisation

Sexual maturity

~2 years

Gestation / incubation

2-4 weeks as a planktonic larva before settling on the bottom

Litter / clutch size

Numerous eggs released by mass spawning

Sources consulted: GBIF; National Marine Sanctuary Foundation; AnAge (genomics.senescence.info); Animal Diversity Web; Oregon Coast Aquarium; California Sea Grant; SeaLifeBase; PMC (larval staging study, extracellular vesicles study); ScienceDirect (Hughes 1989); Science Advances, How colonial animals evolve; Wikipedia, Zooid

The pins mark the dive sites where its presence is documented.