Nereocystis luetkeana

Bull kelp

Authority: (K.Mertens) Postels & Ruprecht

Thallus of this common canopy-forming kelp has a richly branched holdfast (haptera) and a cylindrical stipe 10-36 m (33-118 ft) long, terminating in a single, gas-filled pneumatocyst from which the many blades, up to 10 m (33 ft) long, develop. Blade growth can reach 15 cm (6 in) per day. Reproductive patches (sori) develop on the blades and drop to the seafloor at maturity.

Habitat

This annual kelp grows on rock from the low intertidal to subtidal; it prefers semi-exposed habitats or high current areas. Offshore beds can persist for one to many years, usually in deeper water than Eualaria or Macrocystis, where they co-occur.