Red algae
Red algae, or Rhodophyta (/roʊˈdɒfɪtə/, /ˌroʊdəˈfaɪtə/; from Ancient Greek ῥόδον (rhódon) 'rose', and φυτόν (phutón) 'plant'), make up one of the oldest groups of eukaryotic algae.[3] The Rhodophyta comprises one of the largest phyla of algae, containing over 7,000 recognized species amidst ongoing taxonomic revisions.[4] The majority of species (6,793) are Florideophyceae, and mostly consist of multicellular, marine algae, including many notable seaweeds.[4][5] Red algae are abundant in marine habitats.[6] Approximately 5% of red algae species occur in freshwater environments, with greater concentrations in warmer areas.[7] Except for two coastal cave dwelling species in the asexual class Cyanidiophyceae, no terrestrial species exist, which may be due to an evolutionary bottleneck in which the last common ancestor lost about 25% of its core genes and much of its evolutionary plasticity.[8][9]
Red algae form a distinct group characterized by eukaryotic cells without flagella and centrioles, chloroplasts without external endoplasmic reticulum or unstacked (stroma) thylakoids, and use phycobiliproteins as accessory pigments, which give them their red color.[10] Despite their name, red algae can vary in color from bright green, soft pink, resembling brown algae, to shades of red and purple, and may be almost black at greater depths.[11][12] Unlike green algae, red algae store sugars as food reserves outside the chloroplasts as floridean starch, a type of starch that consists of highly branched amylopectin without amylose.[13] Most red algae are multicellular, macroscopic, and reproduce sexually. The life history of red algae is typically an alternation of generations that may have three generations rather than two.[14] Coralline algae, which secrete calcium carbonate and play a major role in building coral reefs, belong there.
Red algae such as Palmaria palmata (dulse) and Porphyra species (laver/nori/gim) are a traditional part of European and Asian cuisines and are used to make products such as agar, carrageenans, and other food additives.[15]
Applications[edit]
Human consumption[edit]
Red algae have a long history of use as a source of nutritional, functional food ingredients and pharmaceutical substances.[78] They are a source of antioxidants including polyphenols, and phycobiliproteins and contain proteins, minerals, trace elements, vitamins and essential fatty acids.[79][80]
Traditionally, red algae are eaten raw, in salads, soups, meal and condiments. Several species are food crops, in particular dulse (Palmaria palmata)[81] and members of the genus Porphyra, variously known as nori (Japan), gim (Korea), zicai 紫菜 (China), and laver (British Isles).[82]
Red algal species such as Gracilaria and Laurencia are rich in polyunsaturated fatty acids (eicopentaenoic acid, docohexaenoic acid, arachidonic acid)[83] and have protein content up to 47% of total biomass.[78] Where a big portion of world population is getting insufficient daily iodine intake, a 150 ug/day requirement of iodine is obtained from a single gram of red algae.[84] Red algae, like Gracilaria, Gelidium, Euchema, Porphyra, Acanthophora, and Palmaria are primarily known for their industrial use for phycocolloids (agar, algin, furcellaran and carrageenan) as thickening agent, textiles, food, anticoagulants, water-binding agents, etc.[85] Dulse (Palmaria palmata) is one of the most consumed red algae and is a source of iodine, protein, magnesium and calcium.[86] Red algae's nutritional value is used for the dietary supplement of algas calcareas.[87]
China, Japan, Republic of Korea are the top producers of seaweeds.[88] In East and Southeast Asia, agar is most commonly produced from Gelidium amansii. These rhodophytes are easily grown and, for example, nori cultivation in Japan goes back more than three centuries.
Animal feed[edit]
Researchers in Australia discovered that limu kohu (Asparagopsis taxiformis) can reduce methane emissions in cattle. In one Hawaii experiment, the reduction reached 77%. The World Bank predicted the industry could be worth ~$1.1 billion by 2030. As of 2024, preparation included three stages of cultivation and drying. Australia's first commercial harvest was in 2022. Agriculture accounts for 37% of the world’s anthropogenic methane emissions. One cow produces between 154 to 264 pounds of methane/yr.[89]