Seaweed

Seaweed is a common name for macroscopic algae that grow in the ocean. Unlike land plants, seaweeds lack true roots, stems, and leaves. Instead they have holdfasts that grip rocks, flexible stipes that act like stems, and blades that capture sunlight. Some species, such as kelp, can grow more than 30 meters long.

Scientists group seaweeds by pigment: green algae live in shallow water, brown algae like kelp dominate cooler coasts, and red algae thrive deeper where blue light penetrates. Through photosynthesis, seaweeds produce oxygen and absorb carbon dioxide, helping regulate coastal water chemistry.

Seaweeds create underwater forests that shelter fish, crabs, and sea otters. Floating mats of Sargassum provide nursery grounds for sea turtles and eels. Many grazers, including sea urchins and manatees, feed directly on algae, linking seaweed to food webs.

Humans use seaweed for sushi wraps, seasoning, animal feed, biofuels, and fertilizer. Extracts such as agar and carrageenan thicken foods and cosmetics. Sustainable seaweed farms can capture carbon, reduce nutrient pollution, and provide jobs without needing freshwater or fertilizers.

Seaweed faces threats from warming oceans, pollution, and overgrazing when predator populations decline. Restoration projects replant kelp forests, and aquaculture guidelines ensure farms avoid invasive species and respect marine life.