Nereocystis

Nereocystis (Greek, 'mermaid's bladder huki kelp') is a monotypic genus of subtidal kelp containing the species Nereocystis luetkeana. Some English names include edible kelp, bull kelp, bullwhip kelp, ribbon kelp, bladder wrack, and variations of these names. Due to the English name, bull kelp can be confused with southern bull kelps, which are found in the Southern Hemisphere. Nereocystis luetkeana forms thick beds on subtidal rocks, and is an important part of kelp forests.

The species Nereocystis luetkeana was named (as Fucus luetkeanus) after the German-Russian explorer Fyodor Petrovich Litke (also spelled Lütke) by Mertens. The species was renamed in a description by Postels and Ruprecht.

Nereocystis is a brown macroalgae that derives chemical energy from photosynthesis. Nereocystis in particular, similar to Pelagophycus porra, can be identified by a single large pneumatocyst between the end of its hollow stipe and the blades. Individuals can grow to a maximum of 36 m (118 ft). Nereocystis has a holdfast of about 40 cm (16 in), and a single stipe, topped with a pneumatocyst containing carbon monoxide, from which sprout the numerous (about 30-64) blades. The blades may be up to 4 m (13 ft) long, and up to 15 cm (5.9 in) wide. It is usually annual, sometimes persisting up to 18 months. Nereocystis is the only kelp which will drop spore patches, so that the right concentration of spores lands near the parent's holdfast.

The thallus of this common canopy-forming kelp has a richly branched holdfast (haptera) and a cylindrical stipe 10–36 m (33–118 ft) long. The stipe terminates in a single, gas-filled pneumatocyst from which many blades grow. Each blade can grow up to 10 m (33 ft) long, and blade growth can reach 15 cm (5.9 in) per day.

Nereocystis grows in areas where Pterygophora californica also inhabits. Bull kelp will often grow on the stipe of Pterygophora, with up anywhere from 10 to 20 individuals of Nereocystis attaching to a single Pterygophora stipe.

Reproduction in Nereocystis is characterized by an alternation of generations. The diploid generation is the recognizable macroscopic sporophyte. During sexual reproduction, reproductive patches (sori) develop on the blades of the sporophyte and drop to the seafloor at maturity. The sori release haploid spores, which become the microscopic gametophytes. The gametophytes produce gametes, and if fertilization occurs, a new sporophyte organism may develop and begin to grow up from the seafloor.

The species is common along the Pacific Coast of North America, from Southern California to the Aleutian Islands, Alaska. However, drift individuals disperse with ocean currents further south into northwest Baja California, Mexico. Offshore beds can persist for one or many years, usually in deeper water than Eualaria or Macrocystis, where they co-occur.

This annual kelp grows on rock from the low intertidal to subtidal zones; it prefers semi-exposed habitats or high-current areas. It also does not grow in areas with breaking waves or swells. Its distribution is limited by the requirement of light for photosynthesis, and preference for areas of high water movement where the microscopic gametophyte stage will not be covered by sediment.