Red sea urchin, Mesocentrotus franciscanus

About this species

The red sea urchin (Photo: Gerald and Buff Corsi © California Academy of Sciences)

Strongylocentrotidae, a family of sea urchins

Alaska to Baja California


The red sea urchin is the largest species of sea urchin. It can grow up to 18 centimeters in diameter and live to over 100 years of age. They range in color from red to burgundy.

Habitat & Behavior

The red sea urchin lives in shallow water from the low-tide line to greater than 100 meters in depth. It is typically found on rocky shores that are sheltered from wave action. Urchins use special spines to walk, feed, and clean themselves.


While the red sea urchin itself is not a threatened species, it can have a devastating impact on kelp beds. Red sea urchins are kelp-eaters and form high density “mats” that can significantly impact kelp species and the entire kelp ecosystem.

About this map

The bright yellow areas in this map show reef habitat that is more suitable for red sea urchins, while dark blue areas are less suitable. Researchers modeled suitability across all currently known reefs in the Southern California Bight (the dashed gray line shows the extent of the modeled area). The model has a spatial resolution of 200 meters and includes areas shallower than or equal to 45 meters deep.

Red sea urchin (Photo © Jonathan Williams)

Data source: Species distribution model derived from Zellmer et al. 2019 in Frontiers in Marine Science, 6. [link]

Acknowledgements: We would like to thank Amanda J. Zellmer for generously sharing this coastal marine biodiversity data.

References: Sea Grant California. “Red Sea Urchin.” [link]