rødalger

Rödalger, or red algae, are a diverse group of mostly multicellular marine algae within the phylum Rhodophyta. They occur from the intertidal zone to deep waters, with many species in tropical and temperate seas; a few inhabit freshwater. Their reddish color comes from pigments such as phycoerythrin, together with phycocyanin and chlorophyll a. They store energy as floridean starch and typically have cell walls that contain cellulose and gelling polysaccharides such as agar or carrageenan.

Rödalger are characterized by often complex life cycles with alternation of generations. In many Florideophyceae, a carposporophyte stage develops on the female gametophyte, and the life cycle includes a tetrasporophyte stage as well. Most species have non-motile reproductive cells, and some lack flagellated stages entirely. This contrasts with many other algae, which commonly possess motile gametes.

Ecologically, rödalger are important primary producers in coastal ecosystems and contribute to habitat structure on rocky shores and reef-associated environments. They can attach to substrata by holdfasts and range from shallow-water to relatively deep habitats, where their pigments enable absorption of light across various wavelengths.

Economically, rödalger have substantial biotechnological and culinary value. Agar and carrageenan, derived from genera such as Gelidium, Gracilaria, Kappaphycus and Eucheuma, are widely used as gelling and thickening agents. Edible species include nori (Porphyra/Pyropia) and dulse (Palmaria palmata).

Threats include overharvesting, habitat disturbance and climate change, which can affect distribution, productivity and ecosystem interactions.