Details
Mesocentrotus franciscanus
The red sea urchin is a large rocky-coast urchin of the North Pacific. Its long red spines protect a grazing body that can shape kelp communities.
Map: Ecoregions 2017 © RESOLVE (CC BY 4.0) · Natural Earth (PD)
It lives on cool Pacific rocky reefs, kelp forests, and subtidal bottoms. Crevices and seaweed-rich areas often hold dense groups.
Test diameter 8-18 cm; weight 200 g-1 kg. The hard round test is covered with long red to dark red spines. Five strong teeth on the underside scrape algae.
Nocturnal and loosely gregarious, it usually shelters by day. At night it moves slowly with tube feet and spines.
A herbivore, it grazes kelp and attached algae. Where standing kelp is scarce, drifting pieces of seaweed become important food.
Adults release eggs and sperm into the water. Fertilized eggs develop into planktonic larvae that later settle onto rocky bottom.
It is listed as Least Concern. Local densities can swing sharply with predator abundance, kelp supply, and ocean conditions.
