kelps

Kelp refers to several species of large brown algae that form underwater forests in temperate marine environments. The major kelp groups belong to the order Laminariales, including genera such as Macrocystis, Laminaria, Nereocystis, and Durvillaea. They are a type of seaweed, not vascular plants, and can reach several tens of meters in length in favorable conditions.

Kelps have a multicellular thallus with blades, a sturdy stipe, and a holdfast to anchor to rocky substrates. Some species contain gas-filled bladders called pneumatocysts that keep the blades near the surface for light. They are brown algae (Phaeophyceae) in the larger group Stramenopiles. Kelps reproduce by alternation of generations; the dominant, large diploid sporophyte bears sporangia in conceptacles, producing spores that grow into microscopic haploid gametophytes, which then form the sex organs and cycle back to the sporophyte.

Kelp forests are highly productive and biodiverse habitats, providing shelter, foraging grounds, and nursery areas for many fish, invertebrates, and marine mammals. They attenuate wave energy, contribute to carbon sequestration, and influence coastal nutrient cycling. Distribution is largely along nutrient-rich, cold to temperate coasts; giant kelp can form expansive canopies.

Kelps are harvested for alginates used as thickening and stabilizing agents in food and cosmetics, and some species, such as Laminaria, are eaten as kombu in East Asian cuisine. Global kelp forests face pressures from warming oceans, storms, pollution, disease, and overharvesting, leading to declines in some regions; recovery depends on local conditions and protection measures.