Red Urchin

Mesocentrotus franciscanus

Red Urchin

Mesocentrotus franciscanus

Other Common Names
Giant Red Sea Urchins

Rocky Coast

Other Common Names

Giant Red Sea Urchins

At the Aquarium

Rocky Coast

Appearance

These spherical, spiny animals have spines that can reach 2.2 inches long. Their colors range from pink to red to a deep burgundy.

Habitat

Subtidal habitats with a rocky substrate to depths of over 300’, especially in kelp forests and other areas with abundant algae.

Diet

Mostly drift kelp, will also eat intact kelp, foliose algae, and turf algae

Life History

Red sea urchins reproduce by broadcast spawning in spring. Males release their sperm first and this triggers the females to spawn, and each will release several million eggs. The planktonic larval stage lasts 62-131 days, depending on water temperature and food availability, in the form of phytoplankton. Then the larva settles, often on coralline algae, and starts the juvenile life stage. Juveniles may shelter among the spines of adults, mostly often in shallow, wave-exposed habitats or when in the presence of predators.

The largest red sea urchins, at 8.3 inches in diameter, might be over 200 years old.

IUCN Status

Not Evaluated

Ecosystem & Cultural Importance

Other animals rely on red sea urchins. The long spines of red sea urchins provide a protective microhabitat for other species. Besides juvenile red sea urchins, juvenile red and flat abalones, crabs, shrimps, brittle stars, and even fish will seek shelter in the spine canopy of red sea urchins. In addition, when feeding on kelp, they leave bits of kelp behind that are then eaten by other invertebrates that eat detritus that they gather from the substrate, including some brittle stars,

Red Sea Urchins feed a variety of predators, including sea otters, sunflower stars, wolf eels, sheepshead fish, red rock crabs, and white sea urchins.

Red sea urchins are the main target in the urchin fishery because of their large body size. The gonads, called uni, are a delicacy in some countries, including Japan.

Kodiak, Alaska to Baja California, Mexico

Orford Reef in Passages of the Deep is a mini model of the real Orford Reef, a large offshore rocky reef 16 miles northwest of Port Orford. This area contains the majority of Oregon’s kelp bed area and is where the majority of the red sea urchin fishery catch occurs. Between 1986-2022, a total of 20,587 tons of red sea urchins have been caught in Oregon, with 11,733 tons of this through Port Orford. In contrast, during those same years, only 517 tons of red sea urchins have been landed through the Newport port.

Red sea urchins are sensitive to light all over their body. If a shadow suddenly appears, they will exhibit a shadow response, making rapid movements with their spines.

Among an urchin’s spines are small, pincer-like structures called pedicellaria that are used for defense and removing any parasites or organisms looking for a surface to settle on.

Citations & Other Resources

Aquarium of the Pacific
California Department of Fish and Wildlife
GROTH, SCOTT. inchesHistory and Trends in Oregon’s Red Sea Urchin, Mesocentrotus franciscanus, and Purple Sea Urchin, Strongylocentrotus purpuratus, Fisheries, 1986–2022.inches Marine Fisheries Review 85 (2023).
Rogers-Bennett, Laura. inchesThe ecology of Strongylocentrotus franciscanus and Strongylocentrotus purpuratus.inches Developments in Aquaculture and Fisheries Science. Vol. 37. Elsevier, 2007. 393-425.
Wood, Leland. inchesWhere should I settle? An investigation into the larval settlement patterns of Mesocentrotus franciscanus.inches (2019).
Yorke, Christie E., Henry M. Page, and Robert J. Miller. inchesSea urchins mediate the availability of kelp detritus to benthic consumers.inches Proceedings of the Royal Society B 286.1906 (2019): 20190846.

Red Urchin

Red Urchin

Other Common Names

At the Aquarium

Appearance

Habitat

Diet

Life History

IUCN Status

Ecosystem & Cultural Importance

Citations & Other Resources

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