Merilevät

Merilevät, or seaweeds, are several species of marine macroalgae that inhabit coastal waters around the world. They are photosynthetic, multicellular organisms and are traditionally grouped into three main divisions: brown (Phaeophyceae), red (Rhodophyta), and green (Chlorophyta) algae.

Most merilevät attach to rocky substrates by a holdfast and rely on sunlight and tidal exposure. They range from a few centimeters to several meters in length and display a variety of forms, from leaflike blades to bushy thalli. Their life cycles often include alternation of generations, with distinct sporophyte and gametophyte stages that may differ in appearance and reproduction.

Ecologically, merilevät provide habitat and food for many marine organisms, contribute to coastal protection by dampening wave energy, and participate in nutrient cycling. They can be sensitive to changes in water quality, temperature, and light. Overharvesting, habitat destruction, and pollution can threaten certain species, leading to management and conservation considerations.

Humans use merilevät for food and industry. Edible species such as nori (Porphyra/Pyropia), kombu or kelp (Laminaria/Saccharina), and wakame (Undaria) are consumed in various cuisines. They also supply industrial products like alginates, agar, and carrageenan, used as thickeners and stabilizers. Nutritionally, seaweeds are rich in fiber, minerals (including iodine), vitamins, and bioactive compounds such as fucoidan and laminarin.

Harvesting and farming occur through wild collection and mariculture. Seaweed farming typically uses longlines or ropes to cultivate species, helping to alleviate pressure on wild stocks and enable controlled production. Notable species include brown kelps such as Saccharina latissima and Laminaria species, red algae like Porphyra/Pyropia, and various green seaweeds.