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Any of various chiefly aquatic, eukaryotic, photosynthetic organisms, ranging in size from single-celled forms to the giant kelp. Algae were once considered to be plants but are now classified separately because they lack true roots, stems, leaves, and embryos.
[Latin, seaweed.]
algal al'gal (ăl'gəl) adj.An informal assemblage of predominantly aquatic organisms that carry out oxygen-evolving photosynthesis but lack specialized water-conducting and food-conducting tissues. They may be either prokaryotic (lacking an organized nucleus) and therefore members of the kingdom Monera, or eukaryotic (with an organized nucleus) and therefore members of the kingdom Plantae, constituting with fungi the subkingdom Thallobionta. They differ from the next most advanced group of plants, Bryophyta, by their lack of multicellular sex organs sheathed with sterile cells and by their failure to retain an embryo within the female organ. Many colorless organisms are referable to the algae on the basis of their similarity to photosynthetic forms with respect to structure, life history, cell wall composition, and storage products. The study of algae is called algology (from the Latin alga, meaning sea wrack) or phycology (from the Greek phykos, seaweed). See also Bryophyta; Plant kingdom.
General form and structure
Algae range from unicells 1–2 micrometers in diameter to huge thalli [for example, kelps often 100 ft (30 m) long] with functionally and structurally distinctive tissues and organs. Unicells may be solitary or colonial, attached or free-living, with or without a protective cover, and motile or nonmotile. Colonies may be irregular or with a distinctive pattern, the latter type being flagellate or nonmotile. Multicellular algae form packets, branched or unbranched filaments, sheets one or two cells thick, or complex thalli, some with organs resembling roots, stems, and leaves (as in the brown algal orders Fucales and Laminariales). Coenocytic algae, in which the protoplast is not divided into cells, range from microscopic spheres to thalli 33 ft (10 m) long with a complex structure of intertwined siphons (as in the green algal order Bryopsidales).
Classification
Sixteen major phyletic lines (classes) are distinguished on the basis of differences in pigmentation, storage products, cell wall composition, flagellation of motile cells, and structure of such organelles as the nucleus, chloroplast, pyrenoid, and eyespot. These classes are interrelated to varying degrees, the interrelationships being expressed by the arrangement of classes into divisions (the next-higher category). Among phycologists there is far greater agreement on the number of major phyletic lines than on their arrangement into divisions.
Superkingdom Prokaryotae
Kingdom Monera
Division Cyanophycota (= Cyanophyta, Cyanochloronta)
Class Cyanophyceae, blue-green algae
Division Prochlorophycota (= Prochlorophyta)
Class Prochlorophyceae
Superkingdom Eukaryotae
Kingdom Plantae
Subkingdom Thallobionta
Division Rhodophycota (= Rhodophyta, Rhodophycophyta)
Class Rhodophyceae, red algae
Division Chromophycota (= Chromophyta)
Class: Chrysophyceae, golden or golden-brown algae
Prymnesiophyceae (= Haptophyceae)
Xanthophyceae (= Tribophyceae), yellow-green algae
Eustigmatophyceae
Bacillariophyceae, diatoms
Dinophyceae, dinoflagellates
Phaeophyceae, brown algae
Raphidophyceae, chloromonads
Cryptophyceae, cryptomonads
Division Euglenophycota (= Euglenophyta, Euglenophycophyta)
Class Euglenophyceae
Division Chlorophycota (= Chlorophyta, Chlorophycophyta)
Class: Chlorophyceae, green algae
Charophyceae, charophytes
Prasinophyceae
Placing more taxonomic importance on motility than on photosynthesis, zoologists traditionally have considered flagellate unicellular and colonial algae as protozoa, assigning each phyletic line the rank of order. See also Bacillariophyceae; Chrysophyceae; Cryptophyceae; Cyanophyceae; Dinophyceae; Euglenophyceae; Eukaryotae; Eustigmatophyceae; Phaeophyceae; Prasinophyceae; Prochlorophyceae; Prokaryotae; Protozoa; Prymnesiophyceae; Rhodophyceae; Xanthophyceae.
Although some unicellular algae are naked or sheathed by mucilage or scales, most are invested with a covering (wall, pellicle, or lorica) of diverse composition and construction. These coverings consist of at least one layer of polysaccharide (cellulose, alginate, agar, carrageenan, mannan, or xylan), protein, or peptidoglycan that may be impregnated or encrusted with calcium carbonate, iron, manganese, or silica. They are often perforated and externally ornamented. Diatoms have a complex wall composed almost entirely of silica. In multicellular and coenocytic algae, most reproductive cells are naked, but vegetative cells have walls whose composition varies from class to class. See also Cell walls (plant).
Characteristics
Prokaryotic algae lack membrane-bounded organelles. Eukaryotic algae have an intracellular architecture comparable to that of higher plants but more varied. Among cell structures unique to algae are contractile vacuoles in some freshwater unicells, gas vacuoles in some planktonic blue-green algae, ejectile organelles in dinoflagellates and cryptophytes, and eyespots in motile unicells and reproductive cells of many classes. Chromosome numbers vary from n = 2 in some red and green algae to n ≥ 300 in some dinoflagellates. The dinoflagellate nucleus is in some respects intermediate between the chromatin region of prokaryotes and the nucleus of eukaryotes and is termed mesokaryotic. Some algal cells characteristically are multinucleate, while others are uninucleate. Chloroplasts, which always originate by division of preexisting chloroplasts, have the form of plates, ribbons, disks, networks, spirals, or stars and may be positioned centrally or along the cell wall. Photosynthetic membranes (thylakoids) are arranged in distinctive patterns and contain pigments diagnostic of individual classes. See also Cell (biology); Cell plastids; Chromosome;
In all classes of algae except Prochlorophyceae, there are cells that are capable of movement. The slow, gliding movement of certain blue-green algae, diatoms, and reproductive cells of red algae presumably results from extracellular secretion of mucilage. Ameboid movement, involving pseudopodia, is found in certain Chrysophyceae and Xanthophyceae. An undulatory or peristaltic movement occurs in some Euglenophyceae. The fastest movement is produced by flagella, which are borne by unicellular algae and reproductive cells of multicellular algae representing all classes except Cyanophyceae, Prochlorophyceae, and Rhodophyceae.
Internal movement also occurs in algae in the form of cytoplasmic streaming and light-induced orientation of chloroplasts. See also Cell motility; Cilia and flagella.
Sexual reproduction is unknown in prokaryotic algae and in three classes of eukaryotic unicells (Eustigmatophyceae, Cryptophyceae, and Euglenophyceae), in which the production of new individuals is by binary fission. In sexual reproduction, which is found in all remaining classes, the members of a copulating pair of gametes may be morphologically indistinguishable (isogamous), morphologically distinguishable but with both gametes motile (anisogamous), or differentiated into a motile sperm and a relatively large nonmotile egg (oogamous). Gametes may be formed in undifferentiated cells or in special organs (gametangia), male (antheridia) and female (oogonia). Sexual reproduction may be replaced or supplemented by asexual reproduction, in which special cells (spores) capable of developing directly into a new alga are formed in undifferentiated cells or in distinctive organs (sporangia). See also Reproduction (plant).
Most algae are autotrophic, obtaining energy and carbon through photosynthesis. All photosynthetic algae liberate oxygen and use chlorophyll a as the primary photosynthetic pigment. Secondary (accessory) photosynthetic pigments, which capture light energy and transfer it to chlorophyll a, include chlorophyll b (Prochlorophyceae, Euglenophyceae, Chlorophycota), chlorophyll c (Chromophycota), fucoxanthin among other xanthophylls (Chromophycota), and phycobiliproteins (Cyanophyceae, Rhodophyceae, Cryptophyceae). Other carotenoids, especially β-carotene, protect the photosynthetic pigments from oxidative bleaching. Except for different complements of accessory pigments (resulting in different action spectra), photosynthesis in algae is identical to that in higher plants. Carbon is predominantly fixed through the C3 pathway. See also Carotenoid; Chlorophyll.
The source of carbon for most photosynthetic algae is carbon dioxide (CO2), but some can use bicarbonate. Many photosynthetic algae are also able to use organic substances (such as hexose sugars and fatty acids) and thus can grow in the dark or in the absence of CO2. Colorless algae obtain both energy and carbon from a wide variety of organic compounds in a process called oxidative assimilation.
Numerous substances are liberated into water by living algae, often with marked ecological effects. These extracellular products include simple sugars and sugar alcohols, wall polysaccharides, glycolic acid, phenolic substances, and aromatic compounds. Some secreted substances inhibit the growth of other algae and even that of the secreting alga. Some are toxic to fishes and terrestrial animals that drink the water.
Occurrence
Algae are predominantly aquatic, inhabiting fresh, brackish, and marine waters without respect to size or degree of permanence of the habitat. They may be planktonic (free-floating or motile) or benthic (attached). Benthic marine algae are commonly called seaweeds. Substrates include rocks (outcrops, boulders, cobbles, pebbles), plants (including other algae), animals, boat bottoms, piers, debris, and less frequently sand and mud. Some species occur on a wide variety of living organisms, suggesting that the hosts are providing only space. Many species, however, have a restricted range of hosts and have been shown to be (or are suspected of being) at least partially parasitic. All reef-building corals contain dinoflagellates, without which their calcification ability is greatly reduced. Different phases in a life history may have different substrate preferences. Many fresh-water algae have become adapted to a nonaquatic habitat, living on moist soil, masonry and wooden structures, and trees. A few parasitize higher plants (expecially in the tropics), producing diseases in such crops as tea, coffee, and citrus. Thermophilic algae (again, chiefly blue-greens) live in hot springs at temperatures up to 163°F (73°C), forming a calcareous deposit known as tufa. One of the most remarkable adaptations of certain algae (blue-greens and greens) is their coevolution with fungi to form a compound organism, the lichen. See also Lichens; Phytoplankton; Tufa.
Geographic distribution
Fresh-water algae, which are distributed by spores or fragments borne by the wind or by birds, tend to be widespread if not cosmopolitan, their distribution being limited by the availability of suitable habitats. Certain species, however, are characteristic of one or another general climatic zone, such as cold-temperate regions or the tropics. Marine algae, which are spread chiefly by water-borne propagules or reproductive cells, often have distinctive geographic patterns. Many taxonomic groups are widely distributed, but others are characteristic of particular climatic zones or geographic areas. See also Plant geography.
Economic importance
Numerous red, brown, and green seaweeds as well as a few species of fresh-water algae are consumed by the peoples of eastern Asia, Indonesia, Polynesia, and the North Atlantic. Large brown seaweeds may be chopped and added to poultry and livestock feed or applied whole as fertilizer for crop plants. The purified cell-wall polysaccharides of brown and red algae (alginate, agar, carrageenan) are used as gelling, suspending, and emulsifying agents in numerous industries. Some seaweeds have specific medicinal properties, such as effectiveness against worms. Petroleum is generally believed to result from bacterial degradation of organic matter derived primarily from planktonic algae.
Planktonic algae, as the primary producers in oceans and lakes, support the entire aquatic trophic pyramid and thus are the basis of the fisheries industry. Concomitantly, their production of oxygen counteracts its uptake in animal respiration. The ability of certain planktonic algae to assimilate organic nutrients makes them important in the treatment of sewage. See also Food web.
On the negative side, algae can be a nuisance by imparting tastes and odors to drinking water, clogging filters, and making swimming pools, lakes, and beaches unattractive. Sudden growths (blooms) of planktonic algae can produce toxins of varying potency. In small bodies of fresh water, the toxin (usually from blue-green algae) can kill fishes and livestock that drink the water. In the ocean, toxins produced by dinoflagellate blooms (red tides) can kill fishes and render shellfish poisonous to humans.
Fossil algae
At least half of the classes of algae are represented in the fossil record, usually abundantly, in the form of siliceous, calcareous, or organic remains, impressions, or indications. Blue-green algae were among the first inhabitants of the Earth, appearing in rocks at least as old as 2.3 billion years. Their predominance in shallow Precambrian seas is indicated by the extensive development of stromatolites.
All three classes of seaweeds (reds, browns, and greens) were well established by the close of the Precambrian, 600 million years ago (mya). By far the greatest number of fossil taxa belong to classes whose members are wholly or in large part planktonic. Siliceous frustules of diatoms and endoskeletons of silicoflagellates, calcareous scales of coccolithophorids, and highly resistant organic cysts of dinoflagellates contribute slowly but steadily to sediments blanketing ocean floors, as they have for tens of millions of years. Cores obtained in the Deep Sea Drilling Project have revealed an astounding chronology of the appearance, rise, decline, and extinction of a succession of species and genera. From this chronology, much can be deduced about the climate, hydrography, and ecology of particular geological periods. See also Paleobotany; Stromatolite.
Simple plants that do not show differentiation into roots, stems, and leaves. They are mostly aquatic—either seaweeds or pond and river-weeds. Some seaweeds, such as dulse and Irish moss, have long been eaten, and a number of unicellular algae, including Chlorella, Scenedesmus, and Spirulina spp. have been grown experimentally as novel sources of food (50-60% of the dry weight is protein).
A large and diverse group of simple plants that contain chlorophyll and can therefore photosynthesize. Algae live in aquatic habitats or in moist regions inland.
For more information on algae, visit Britannica.com.
Types of Algae
The simplest algae are single cells (e.g., the diatoms); the more complex forms consist of many cells grouped in a spherical colony (e.g., Volvox), in a ribbonlike filament (e.g., Spirogyra), or in a branching thallus form (e.g., Fucus). The cells of the colonies are generally similar, but some are differentiated for reproduction and for other functions. Kelps, the largest algae, may attain a length of more than 200 ft (61 m). Euglena and similar genera are free-swimming one-celled forms that contain chlorophyll but that are also able, under certain conditions, to ingest food in an animallike manner. The green algae include most of the freshwater forms. The pond scum, a green slime found in stagnant water, is a green alga, as is the green film found on the bark of trees. The more complex brown algae and red algae are chiefly saltwater forms; the green color of the chlorophyll is masked by the presence of other pigments. Blue-green algae have been grouped with other prokaryotes in the kingdom Monera and renamed cyanobacteria.
See the separate phyla (divisions) Chlorophyta, Euglenophyta, Dinoflagellata, Chrysophyta, Phaeophyta, Rhodophyta.
Uses of Algae
Algae, the major food of fish (and thus indirectly of many other animals), are a keystone in the aquatic food chain of life; they are the primary producers of the food that provides the energy to power the whole system. They are also important to aquatic life in their capacity to supply oxygen through photosynthesis. Seaweeds, e.g., the kelps (kombu) and the red algae Porphyra (nori), have long been used as a source of food, especially in Asia. Both cultivated and naturally growing seaweeds have been harvested in the Pacific Basin for hundreds of years. Kelp are also much used as fertilizer, and kelp ash is used industrially for its potassium and sodium salts. Other useful algae products are agar and carrageen, which is used as a stabilizer in foods, cosmetics, and paints.
Bibliography
See H. C. Bold and M. J. Wynne, Introduction to the Algae: Structure and Reproduction (1985); C. A. Lembi and J. R. Waaland, Algae and Human Affairs (1988); C. van den Hoek, Algae: an Introduction to Phycology (1994).
Primitive organisms that contain chlorophyll but do not have structures, such as xylem and phloem, to transport fluids. Algae sometimes contain only a single cell, and nowadays they are not considered members of the plant kingdom.
Pertaining to or caused by algae.
A flowerless plant of extremely simple structure, usually green but in the seaweeds often beautifully colored. Algae range in size from the microscopic organisms that cover ponds with green scum to the giant kelp, a seaweed more than 100 feet long.
Algae have conventionally been regarded as simple plants within the study of botany. All are Eukaryota, though Chromophyta have Bacterial (see Blue-green algae) characteristics and some authorities consider them all to be Protists, however this view is now considered to be outdated.[1] They may still be included in the algae as plants. Some authors often include the blue-green algae (Cyanophyta) but note that they are not eukaryote. Algae
do not represent a single evolutionary direction or line but a level of organization that may have developed several times in the
early history of life on Earth.
The protists are traditionally considered more animal-like (see Protozoa).
The prokaryotic forms, referred to as blue-green algae are only half-algae with a mixture of bacterial characteristics. However, they are quite distant from the bacteria and are referred to by some as Cyanochloronta. All other forms belong as true eukaryota algae within the study of Botany, they have a nucleus enclosed within a membrane.[2] The protoctists are defined by some as eukaryotic microorganisms with the exception of animals and plants and including fungi and algae, slime moulds and other obscure eukaryotes.[3] There is still some disagreement on some of these matters.
Algae range from single-cell organisms to multicellular organisms, some with fairly complex differentiated form and (if marine) called
seaweeds. All lack leaves, roots,
flowers, seeds and other organ structures that characterize higher plants (vascular
plants). They are distinguished from other protozoa in that they are
All algae have photosynthetic machinery ultimately derived from the cyanobacteria, and so produce oxygen as a byproduct of photosynthesis, unlike non-cyanobacterial photosynthetic bacteria. It is estimated that algae produce about 73 to 87 percent of the net global production of oxygen[4] - which is available to humans and other animals for respiration.
Algae are usually found in damp places or bodies of water and thus are common in terrestrial as well as aquatic environments. However, terrestrial algae are usually rather inconspicuous and far more common in moist, tropical regions than dry ones, because algae lack vascular tissues and other adaptations to live on land. Algae can, however, endure dryness and other conditions in symbiosis with a fungus as lichen.
The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column — called phytoplankton — provide the food base for most marine food chains. In very high densities (so-called algal blooms) these algae may discolor the water and outcompete or poison other life forms. Seaweeds grow mostly in shallow marine waters, however some have been recorded to a depth of 300 m.[2]Some are used as human food or harvested for useful substances such as agar or fertilizer.
The study of marine and freshwater algae is called phycology or algology.
The US Algal Collection is represented by almost 300,000 accessioned and inventoried herbarium specimens.[1]
Cyanobacteria have been included among the algae, referred to as the cyanophytes or Blue-green algae, (the term "algae" refers to any aquatic organisms capable of photosynthesis)[5] though some recent treatises on algae specifically exclude them. Cyanobacteria are some of the oldest organisms to appear in the fossil record dating back to the Precambrian, possibly as far as about 3.5 billion years.[6] Ancient cyanobacteria likely produced much of the oxygen in the Earth's atmosphere.
Cyanobacteria can be unicellular, colonial, or filamentous. They have a prokaryotic cell structure typical of bacteria and conduct photosynthesis on specialized cytoplasmic membranes called thylakoid membranes, rather than in organelles. Some filamentous blue-green algae have specialized cells, termed heterocysts, in which nitrogen fixation occurs.[7] the perfect prokaryotic cell consist of miscalgnous sheath covering cellwall that consistof pectinic substance and sachride while the cellwall consist of 4 layer outer and inner and middle layer while the fourth layer is attached to plasma membrane and the protoplast consist of 2 part peripheral coloured partknown by chromatoplasm which contain the pigments in case of algae and contain photothynsis producte.g in cyanobacteria it contain chlorophylla, b-caroteinand c-phycocyanin and c-phycoerthyrin
All other algae are eukaryotes and conduct photosynthesis within membrane-bound structures (organelles) called chloroplasts. Chloroplasts contain DNA and are similar in structure to cyanobacteria, presumably representing reduced cyanobacterial endosymbionts. The exact nature of the chloroplasts is different among the different lines of algae, reflecting different endosymbiotic events. The table below lists the three major groups of eukaryotic algae and their lineage relationship is shown in the figure on the left. Note many of these groups contain some members that are no longer photosynthetic. Some retain plastids, but not chloroplasts, while others have lost them entirely.
| Supergroup affiliation | Members | Endosymbiont | Summary |
|---|---|---|---|
| Primoplantae/ Archaeplastida |
Cyanobacterium | These algae have primary chloroplasts, i.e. the chloroplasts are surrounded by two membranes and probably developed through a single endosymbiosis. The chloroplasts of red algae have a more or less typical cyanobacterial pigmentation, while those of the green alga have chloroplasts with chlorophyll a and b, the latter found in some cyanobacteria and not most. Higher plants are pigmented similarly to green algae and probably developed from them. | |
| Cabozoa or Excavata and Rhizaria |
Green alga |
These groups have green chloroplasts containing chlorophyll b. Their chloroplasts are surrounded by three and four membranes, respectively, and were probably retained from an ingested green alga. Chlorarachniophytes, which belong to the phylum Cercozoa, contain a small nucleomorph, which is a relict of the alga's nucleus. Euglenids, which belong to the phylum Euglenozoa, have chloroplasts with only three membranes. It has been suggested that the endosymbiotic green algae were acquired through myzocytosis rather than phagocytosis. |
|
| Chromalveolata or Chromista and Alveolata |
Red alga |
These groups have chloroplasts containing chlorophylls a and c. The latter chlorophyll type is not known from any prokaryotes or primary chloroplasts, but genetic similarities with the red algae suggest a relationship there. In the first three of these groups (Chromista), the chloroplast has four membranes, retaining a nucleomorph in cryptomonads, and they likely share a common pigmented ancestor. The typical dinoflagellate chloroplast has three membranes, but there is considerable diversity in chloroplasts among the group, as some members have acquired theirs from different sources. The Apicomplexa, a group of closely related parasites, also have plastids called apicoplasts. Apicoplasts are not photosynthetic but appear to have a common origin with dinoflagellates chloroplasts. |
It was W.H.Harvey (1811 — 1866) who first divided the algae into four divisions based on their pigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey's four divisions were: red algae (Rhodophyta), brown algae (Heteromontophyta), green algae (Chlorophyta) and Diatomaceae (Dixon, 1973 p.232).[8]
Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and non-motile forms have developed independently among several of the groups. Some of the more common organizational levels, more than one of which may occur in the life cycle of a species, are
In three lines even higher levels of organization have been reached, imma hit with full tissue differentiation. These are the brown algae [2]—some of which may reach 50 m in length (kelps)[9]—the red algae [3], and the green algae [4]. The most complex forms are found among the green algae (see Charales and Charophyta), in a lineage that eventually led to the higher land plants. The point where these non-algal plants begin and algae stop is usually taken to be the presence of reproductive organs with protective cell layers, a characteristic not found in the other alga groups.
The first plants on earth were algae and these still thrive in a range of aquatic habitats today. The land plants evolved from the algae, more specifically green algae. Some 400 million years ago freshwater, green, filamentous algae invaded the land. These probably had an isomorphic alternation of generations and were probably heterotrichous. Fossils of isolated land plant spores suggest land plants may have been around as long as 475 million years ago.
Some species of algae form symbiotic relationships with other organisms. In these symbioses, the algae supply photosynthates (organic substances) to the host organism providing protection to the algal cells. The host organism derives some or all of its energy requirements from the algae. Examples include
Rhodophyta, Chlorophyta and Heterokontophyta, the three main algal Phyla, have life-cycles which show tremendous variation with considerable complexity. In general there is an asexual phase where the seaweed's cells are diploid, a sexual phase where the cells are haploid followed by fusion of the male and female gametes. Asexual reproduction is advantageous in that it permits efficient population increases, but less variation is possible. Sexual reproduction allows more variation but is more costly because of the waste of gametes that fail to mate, among other things. Often there is no strict alternation between the sporophyte and gametophyte phases and also because there is often an asexual phase, which could include the fragmentation of the thallus.[9][11][5]
In the British Isles the UK Biodiversity Steering Group Report estimated there to be 20,000 algal species in the UK, freshwater and marine, about 650 of these are seaweeds. Another checklist of freshwater algae reported only about 5000 species. It seems therefore that the 20,000 is an overestimate or an error (John, 2002 p.1).[12]
World-wide it is thought that there are over 5,000 species of red algae, 1,500 — 2,000 of brown algae and 8,000 of green algae. In Australia it is estimated that there are over 1,300 species of red algae, 350 species of brown algae and approximately 2,000 species of green algae totalling 3,650 species of algae in Australia.[13]
Around 400 species appear to be an average figure for the coastline of South African west coast.[14]
669 marine species have been described from California (U.S.A.).[15]
642 entities are listed in the check-list of Britain and Ireland (Hardy and Guiry, 2006).[16]
No publication has been found which attempts to discuss the general distribution of algae in the seas world-wide. However, notes and comments have been made by some authors. The floristic discontinuities may appear to determined by geographical features such as Antarctica, long distances of ocean or general land masses. However, the distances between Norway, the Faroes and Iceland do not show great changes in distribution.[2]
There has been dispersal in some species by ships, water currents and the like, further some algae drifting algae can quickly become entangled and easily drift.[17] Two red species have been introduced from the Pacific to Europe and the Mediterranean: Bonnemaisonia hamifera Hariot and Asparagopsis armata Harvey,[18] A. armata is a native of Australia.[2][6]Colpomenia peregrina is a native of the Pacific but has also invaded Europe
For centuries seaweed has been used as a fertilizer; Orwell writing in the 16th Century referring to drift weed in South Wales: "This kind of ore they often gather and lay in heaps where it heats and rots, and will have a strong and loathsome smell; when being so rotten they cast it on the land, as they do their muck, and thereof springeth good corn, especially barley" and "After spring tides or great rigs of the sea, they fetch it in sacks on horse brackets, and carry the same three, four, or five miles, and cast it on the lande, which doth very much better the ground for corn and grass" (Chapman p.35).[19]
Algae are used by humans in many ways. They are used as fertilizers, soil conditioners and are a source of livestock feed.[9] Because many species are aquatic and microscopic, they are cultured in clear tanks or ponds and either harvested or used to treat effluents pumped through the ponds. Algaculture on a large scale is an important type of aquaculture in some places.
Maerl is commonly used as a soil conditioner, it is dredged from the sea floor and crushed to form a powder.[9] It is still harvested around the coasts of Brittany in France and off Falmouth, Cornwall (also extensively in western Ireland) and is a popular fertilizer in these days of organic gardening investigated Falmouth maerl and found that L. corallioides predominated down to 6 m and P. calcareum from 6-10 m (Blunden et al., 1981).[20][21]
Chemical analysis of maerl showed that it contained 32.1% CaCO3 and 3.1% MgCO3 (dry weight).
Chondrus crispus, (probably confused with Mastocarpus stellatus, common name: Irish moss), is also used as "carrageen". The name carrageenan comes from the Irish Gaelic for Chondrus crispus. It is an excellent stabiliser in milk products - it reacts with the milk protein caesin, other products include: petfoods, toothpaste, ice-creams and lotions etc.[14][[#wp-_note-Lewis et al 88|[22]]] Alginates in creams and lotions are absorbable through the skin.[23]
Seaweeds are an important source of food, especially in Asia; They are excellent sources of many vitamins including: A, B1, B2, B6, niacin and C. They are rich in iodine, potassium, iron, magnesium and calcium.[24]
Algae is commercially cultivated as a nutritional supplement. One of the most popular microalgal species is Spirulina (Arthrospira platensis), which is a Cyanobacteria (known as blue-green algae), and has been hailed by some as a superfood.[12] Other algal species cultivated for their nutritional value include; Chlorella (a green algae), and Dunaliella (Dunaliella salina), which is high in beta-carotene and is used in vitamin C supplements.
In China at least 70 species of algae are eaten as is the Chinese "vegetable" known as fat choy (which is actually a cyanobacterium). Roughly 20 species of algae are used in everyday cooking in Japan.[24]
Certain species are edible; the best known, especially in Ireland is Palmaria palmata (Linnaeus) O. Kuntze (Rhodymenia palmata (Linnaeus) Kuntze, common name: dulse).[13] This is a red alga which is dried and may be bought in the shops in Ireland. It is eaten raw, fresh or dried, or cooked like spinach. Similarly, Durvillaea Antarctica [14] is eaten in Chile, common name: cochayuyo. [15]
Porphyra (common name: purple laver), is also collected and used in a variety of ways
(e.g. "laver bread" in the British Isles). In Ireland it is collected and made into a jelly by stewing or boiling. Preparation
also involves frying with fat or converting to a pinkish jelly by heating the fronds in a saucepan with a little water and
beating with a fork. It is also collected and used by people parts of Asia, specifically China and Japan as nori and along most of the coast from California to
British Columbia. The Hawaiians and the Maoris of
One particular use is in "instant" puddings, sauces and creams. Ulva lactuca (common name: sea lettuce), is used locally in Scotland where it is added to soups or used in salads. Alaria esculenta (common name: badderlocks or dabberlocks), is used either fresh or cooked, in Greenland, Iceland, Scotland and Ireland.
The oil from some algae have high levels of unsaturated fatty acids. Arachidonic acid (a polyunsaturated fatty acid), is very high in Parietochloris incisa, (a green alga) where it reaches up to 47% of the triglyceride pool (Bigogno C et al. Phytochemistry 2002, 60, 497). [16] [17]
There are also commercial uses of algae as agar.[[#wp-_note-Lewis et al 88|[22]]]
The natural pigments produced by algae can be used as an alternative to chemical dyes and coloring agents.[18] Many of the paper products used today are not recyclable because of the chemical inks that they use, paper recyclers have found that inks made from algae are much easier to break down. There is also much interest in the food industry into replacing the coloring agents that are currently used with coloring derived from algal pigments. In Israel, a species of green algae is grown in water tanks, then exposed to direct sunlight and heat which causes it to become bright red in color. It is then harvested and used as a natural pigment for foods such as Salmon. [19]
Between 100,000 and 170,000 wet tons of Macrocystis are harvested annually in California for alginate extraction and abalone feed.[20] [21]
Seaweed specimens can be collected and preserved for research. Such preserved specimens will keep for two or three hundred years. Those of Carl von Linné (1707 — 1778) are still available for reference, and are used. Specimens may be collected from the shore; those below low tide must be collected by diving or dredging. The whole algal specimen should be collected, that is the holdfast, stipe and lamina. Specimens of algae reproducing will be the more useful for identification and research. When collected the details of the location and site should be noted. They can then be preserved pressed on paper or in a preserving liquid such as alcohol or solution of 5 per cent formalin/seawater. However, formalin is reported to be carcinogenic.[13]
The ecology of the shores of the British Isles, including a discussion of the different shores from sheltered to exposed along with an exposure scale, is given by Lewis (1964).[25] An exposure scale of five stages is given:- Very Exposed Shores; Exposed Shores; Semi-exposed Shores; Sheltered Shores and Very Sheltered Shores. Factors indicating the differences between these exposure scales are detailed. Very Exposed Shores have a wide Verrucaria zone entirely above the upper tide level, a Porphyra zone above the barnacle level and Lichina pygmaea is locally abundant.
