Purple Urchin

Scientific Name Strongylocentrotus purpuratus

Native To Northern Pacific Coast from Alaska to Mexico

Habitat Lower Intertidal zone and kelp forest

Diet kelp and algae

Size and Age Can grow to be 10 cm in diameter and could live as long as 70 years

Natural History

Purple sea urchins, like other urchins, are spiny creatures whose bodies are comprised of a test (a calcified body covering or “shell”) which is covered in spines which protect it. A purple urchin’s mouth is located on the bottom of its body, conveniently placed so that is may feed on the kelp forests in which it lives, as it uses its spines and tube feet to move around. Frequently preyed upon by sea otters, if their numbers are left unchecked, they can cause ocean desertification by wiping out whole kelp forests.

Near Threatened

Conservation Status

Many ocean invertebrates requires delicate and balanced conditions to survive. For this reason they are known as an indicator species. When ocean conditions change, ocean invertebrates are the first to be affected. Rising ocean temperatures and ocean acidification (from urban and agricultural run-off) are some of the factors that alter the water quality of our oceans.

Urchin populations historically have been overfished, making the populations of urchins too small to be considered a sustainable sea food option.

Interesting Facts

  • The mouth of an urchin is called Aristotle’s lantern and is comprised of 5 tiny teeth
  • With their mouth located on the bottom of their body, their waste is excreted through the top of their body.
  • Urchins will protect themselves from Sea stars by pinching at their tube feet when they get too close. However they cannot protect against sunflower stars who can swallow urchins whole.
  • Urchin populations are kept steady by sea otters and sunflower stars. Without these predators, purple urchins can wipe out kelp forests because they travel as hordes.