Mesocentrotus franciscanus is a large species of sea urchin in the family Strongylocentrotidae, commonly known as the red sea urchin of the northeastern Pacific. It is native to the Pacific coast of North America, ranging from Alaska through British Columbia and the Pacific Northwest to Baja California, where it inhabits rocky subtidal zones and kelp forest ecosystems. The genus name Mesocentrotus derives from Greek mesos meaning “middle” and kentron meaning “spine”, referring to morphological characteristics intermediate between related sea urchin genera, while the species epithet franciscanus means “of San Francisco,” referencing the region where it was first scientifically described.

Historically, this species has been harvested by Indigenous coastal peoples of the Pacific Northwest, including Haida, Tlingit, Coast Salish, and other groups, who consumed the roe seasonally. In modern times it supports a significant commercial fishery, particularly in California and British Columbia, supplying uni to Japanese and global sushi markets. The edible portion consists of the gonads, which are prized for their sweet, briny flavor and creamy texture and are eaten raw, lightly cured, or incorporated into sauces and seafood dishes.

Its roe is nutritionally notable for high levels of long-chain omega-3 fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), both associated with anti-inflammatory and cardioprotective effects. It also contains echinochrome A, a polyhydroxylated naphthoquinone pigment with antioxidant activity; ovothiol, a sulfur-containing antioxidant thiol compound; and carotenoids such as β-carotene and astaxanthin, which contribute to coloration and antioxidant capacity.