brownalgae

Brown algae, or Phaeophyceae, are a diverse group of mostly marine, multicellular algae. They range from simple filamentous forms to large kelps and are common in temperate and cold coastal waters worldwide. Many species form extensive kelp forests that provide habitat, shelter, and food for coastal marine communities.

The characteristic brown color arises from fucoxanthin, a carotenoid that masks chlorophyll. Brown algae also contain chlorophylls a and c and various xanthophylls. They store energy mainly as laminarin and the sugar mannitol, and their cell walls contain cellulose and alginates. Alginate is extracted commercially as a thickener and stabilizer used in foods, cosmetics, and industrial products.

Morphology and life cycle: Brown algae are multicellular with a thallus that often includes a holdfast, a stalk-like stipe, and leaf-like blades; many species possess gas-filled bladders to lift the blades toward light. Their life cycle typically features alternation of generations, usually with a diploid sporophyte producing zoospores that grow into haploid male and female gametophytes, which in turn produce gametes that fuse to form a new diploid sporophyte.

Ecology and human use: They form kelp forests that support high biodiversity and provide coastal protection. They are sensitive to ocean warming, pollution, and grazing by herbivores, with declines observed in some regions. Economically, they supply alginates and edible seaweeds such as kombu and wakame, contributing to food industries and nutrition.