redalgae

Red algae, or Rhodophyta, are a diverse group of mostly marine algae that range from small filamentous forms to large seaweeds. They are predominantly multicellular and occur in coastal and subtidal habitats, from shallow waters to depths where light is limited. The characteristic red color comes from phycoerythrin, a light-harvesting pigment that complements chlorophyll a and phycobiliproteins and allows photosynthesis under blue-green light.

Structure and pigments: Their thalli are typically simple to complex; their cell walls contain cellulose and various sulfated polysaccharides such as agar and carrageenan, which are widely used in food and industry. They store energy as floridean starch, distinct from plant starch.

Life cycle: Red algae exhibit diverse reproductive strategies, often with complex alternation of generations. Most have oogamous fertilization and produce a carposporophyte stage on the female thallus. The life cycles can be triphasic, with gametophyte, carposporophyte, and tetrasporophyte phases, some of which are isomorphic.

Ecology and distribution: They are predominantly marine and abundant on rocky coasts, reefs, and tidal zones, but some species inhabit freshwater. Phycoerythrin permits growth at low light, contributing to their presence at greater depths than many other algae. Some red algae are parasitic on other algae or plants.

Human use: Red algae are important ecologically and economically. Gel-forming polysaccharides such as agar, agarose, and carrageenan are extracted from various species and used as food thickening agents, microbiological media, and in cosmetics. Edible red algae include species such as nori (Porphyra) and dulse (Palmaria).