10/10/2026
Happy Seaweed Saturday! Let’s dive deep into the subtidal of Southern California to find the magnificent Elk Kelp, or Pelagophycus p***a. Elk kelp grow in the California Channel Islands and along the mainland from San Diego to Baja California at depths of 50-125 feet. It is easily identified by its large gas-filled pneumatocysts, branched “antlers”, and corrugated blades. The stipe can grow up to 90 feet in length, and some blades up to 65 ft! The stipe is solid and cylindrical throughout most of its length but widens and hollows out beneath the pneumatocyst. The “antlers” that emerge from the pneumatocyst are flat branches that initially divide dichotomously, after which they branch sympodially to form blades. The stipe length, number and texture of blades, size, and shape of the pneumatocyst differ between sheltered, soft sediment habitats on the leeward side of islands and exposed, rocky reefs on the mainland and windward sides of islands. These morphological differences were once the basis for descriptions of three species in the genus. Currently,we know that though all populations belong to one species, they are diverging genetically.
Like other kelps, the life cycle is heteromorphic and diplohaplontic. When fertile, the blades of the large diploid sporophyte bear dark-colored patches of spores that are released and settle on the ocean floor. These spores develop into microscopic, filamentous gametophytes that produce gametes that fuse to grow into the next sporophyte generation.
Elk kelp populations establish at great depths where light is limited because both gametophytes and young sporophytes are sensitive to high irradiance levels. However, some older individuals can acclimate to higher irradiance and may occur in shallower water.
Elk kelp forests create habitat structure for many species of fish and invertebrates, and senescent thalli either float or wash ashore, providing food and habitat for animals in pelagic and beach environments.
