Elk Kelp, Pelagophycus porra
Elk Kelp, Pelagophycus porra, showing laminae. Underwater photograph taken in coastal waters off San Diego, California, September 2025. Photograph and identification of Bob Hillis, Ivins, Utah.
Elk Kelp, Pelagophycus porra, showing pneumatocyst and branching “antlers.” Underwater photograph taken in coastal waters off San Diego, California, September 2025. Photograph and identification of Bob Hillis, Ivins, Utah.
Phylogeny: Elk Kelp, Pelagophycus porra (Léman) Setchell, 1908, is a brown algae in the Laminariaceae Family of Kelp. The Pelagophycus genus is one of fourteen genera in the Laminariaceae Family and this species is the only species in the Pelagophycus genus. Algae in this family are not from the plant kingdom, but are from the Chromista kingdom. Chromists are photosynthesizing organisms that used to be known as Protista. This diverse kingdom includes brown algae, diatoms, mildew, and malarial parasites. The genus name Pelagophycus comes from the Greek words meaning “open sea algae”. The species name porra comes from Latin and means “leek” or “club”, referring to the shape of the top of the stipe. They are also known as Antler Kelp, Bladder Kelp, Bull Kelp and Sea-leek.
Morphology: Like other kelps, Elk Kelp resembles a plant in appearance, but the resemblance stops there. The thallus (body of the organism) is comprised of three organs: the holdfast, the stipe, and the lamina. The thallus is held to the bottom substrate by a root-like holdfast. The intertwined and branched haptera tissue of the holdfast anchors the plant, but does not gather nutrients or water like a root does. The stem-like stipe provides structure and connects the holdfast to the laminae. The stipes are smooth, round in cross section, and flexible. The stipe widens toward its top and then terminates in a large spherical pneumatocyst (gas-filled bladder). Branching from the top of the pneumatocyst is an antler like structure which supports the leaf-like laminae. The laminae are long, wide, and blade-like. The laminae are leathery and corrugated. There may be soft spines along the margins of the laminae. The pneumatocysts lift the stipe and laminae toward the surface where the sunlight is most intense. Giant Kelp uses chlorophyll A and chlorophyll C for photosynthesis. The brown color comes primarily from these chemicals and fucoxanthin. Elk Kelp is the second longest kelp in the world, with the first being Giant Kelp, Macrocystis pyrifera. Elk Kelp can reach 27 m (89 feet) in length. The laminae can reach 2 m (6 feet 6 inches) in width and 20 m (66 feet) in length.
Habitat and Distribution: Elk Kelp can grow on mud stone, pebbles, rocks, sand, and sand stone substrate. Individuals in more protected waters can grow on softer substrates. They grow deeper than most kelps and is often found seaward of Giant Kelp forests. Elk Kelp grows at depths from 12 m (39 feet) to 90 m (295 feet). The Elk Kelp is a subtropical Eastern Pacific species that has a limited range in Mexican waters being found from Isla Natividad, Baja California Sur, northward along the central and northwest coasts of the Baja Peninsula.
Reproduction: Elk Kelp alternates between an asexual sporophyte generation and a sexual gametophyte generation. Adult sporophytes reproduce asexually through the production of spores, which produce gametophytes. Gametophytes are microscopic and produce either male (sperm) or female (eggs) gametes. The gametophytes release their gametes into the water where fertilization occurs and forms a zygote, which grows into a juvenile sporophyte. The sporophyte matures and completes the cycle.
Ecosystem Interactions: Elk Kelp is a critical part of many ecosystems. It provides food, structure, and camouflage for hundreds of species of fish, mollusks, crustaceans, and other invertebrates. As the lamina and stipes mature and slough off, or are torn lose by water movement, they continue to provide food and habitat whether they sink to the bottom, wash up on the beach, or drift into pelagic waters as a kelp paddy.
Human Interactions: Elk Kelp contains many chemicals which are used in the medical, cosmetic, food processing, aquacultural, manufacturing, and agricultural industries. From a conservation perspective the Elk Kelp has not been evaluated. It is common and has a fairly wide range and would probably be considered to be of Least Concern.
Synonyms: Durvillaea porra, Laminaria porra, Nereocystis gigantea, Pelagophycus giganteus, and Pelagophycus intermedius.