kelp

Kelp refers to several species of large brown algae in the order Laminariales. They are a group of brown algae (Phaeophyceae) that form underwater forests in temperate coastal waters.

Most kelp species have a holdfast that anchors to rock, a flexible stipe, and broad blade-like fronds. Some possess gas-filled bladders that help the blades reach toward the surface to access sunlight.

Kelp has a life cycle that alternates between a diploid sporophyte, which is the visible plant, and microscopic haploid gametophytes. The sporophyte produces sporangia in structures called conceptacles; spores grow into male and female gametophytes, which fertilize to form new sporophytes.

Kelp forests support diverse communities, providing habitat, shelter, and feeding grounds for fish, invertebrates, and marine mammals. They contribute to high primary production, nutrient cycling, and coastal protection, and they can influence local hydrology and sediment dynamics.

Humans harvest kelp for food and industrial uses. Edible kelp such as kombu is common in East Asian cuisines. Alginate, extracted from brown algae, is widely used as a thickener and stabilizer in foods and cosmetics.

Kelp populations face threats from rising ocean temperatures, pollution, and storm events. Overgrazing by herbivores after loss of predators, disease, and coastal development can reduce forests.

Notable kelp species include Macrocystis pyrifera (giant kelp), Nereocystis luetkeana (bull kelp), Saccharina latissima, and Laminaria digitata, which form extensive forests in different regions.