Rhodophyta: Red Algae - Seaweed

Rhodophyta: Red Algae - Seaweed
Examples: Palmaria, Delesseria, Chondrus, Coralline algae

Characteristics: The red colour of these algae results from the pigments phycoerythrin and phycocyanin; this masks the other pigments, Chlorophyll a (no Chlorophyll b), beta-carotene and a number of unique xanthophylls. The main reserves are typically floridean starch, and floridoside; true starch like that of higher plants and green algae is absent. The walls are made of cellulose and agars and carrageenans, both long-chained polysaccharide in widespread commercial use. There are some unicellular representatives of diverse origin; more complex thalli are built up of filaments.

A very important group of red algae is the coralline algae, which secrete calcium carbonate onto the surface of their cells. Some of these corallines are articulated (right, Corallina, with flexible erect branches; others are crustose (below). These corallines have been used in bone-replacement therapies. Coralline algae were used in ancient times as vermifuges, thus the binomial Corallina officinalis.

Several red algae are eaten: best known amongst these is dulse (Palmaria palmata above) and Carrageen Moss (Chondrus crispus and Mastocarpus stellatus).

However, Nori, popularised by the Japanese is the single most valubable marine crop grown by aquaculture with a value in excess of US$1 billion. More information on aquaculture.

The red algae Kappaphycusand Betaphycus are now the most important sources of carrageenan, a commonly used ingredient in food, particuarly yoghurts, chocolate milk and repared puddings. Gracilaria, Gelidium, Pterocladia and other red algae are used in the manufacture of the all-important agar, used widely as a growth medium for microorganisms and for biotechnological applications.

AlgaeBase dynamic species counts shows that there are about 9,300 species of seaweeds, of which about 6,000 are red algae (Rhodophyta), the vast majority of which are marine. These are found in the intertidal and in the subtidal to depths of up to 40, or occasionally, 250 m. The main biomass of red algae worldwide is provided by the Corallinaceae and Gigartinaceae.

Chlorophyta: Green Algae - Seaweed

Chlorophyta: Green Algae - Seaweed
Examples: Chlorella, Chlamydomonas, Spirogyra, Ulva.

Characteristics: Green colour from chlorophyll a and b in the same proportions as the 'higher' plants; beta-carotene (a yellow pigment); and various characteristic xanthophylls (yellowish or brownish pigments). Food reserves are starch, some fats or oils like higher plants. Green algae are thought to have the progenitors of the higher green plants but there is currently some debate on this point.

Green algae may be unicellular (one cell), multicellular (many cells), colonial (living as a loose aggregation of cells) or coenocytic (composed of one large cell without cross-walls; the cell may be uninucleate or multinucleate). They have membrane-bound chloroplasts and nuclei. Most green are aquatic and are found commonly in freshwater (mainly charophytes) and marine habitats (mostly chlorophytes); some are terrestrial, growing on soil, trees, or rocks (mostly trebouxiophytes). Some are symbiotic with fungi giving lichens. Others are symbiotic with animals, e.g. the freshwater coelentrate Hydra has a symbiotic species of Chlorella as does Paramecium bursaria, a protozoan. A number of freshwater green algae (charophytes, desmids and Spirogyra) are now included in the Charophyta (charophytes), a phylum of predominantly freshwater and terrestrial algae, which are more closely related to the higher plants than the marine green algae belonging to the Chlorophyta (known as chlorophytes). Other green algae from mostly terrestrial habitats are included in the Trebouxiophyceae, a class of green algae with some very unusual features.

Asexual reproduction may be by fission (splitting), budding, fragmentation or by zoospores(motile spores). Sexual reproduction is very common and may be isogamous (gametes both motile and same size); anisogamous (both motile and different sizes - female bigger) or oogamous (female non-motile and egg-like; male motile). Many green algae have an alternation of haploid and diploid phases. The haploid phases form gametangia (sexual reproductive organs) and the diploid phases form zoospores by reduction division (meiosis). Some do not have an alternation of generations, meiosis occurring in the zygote.

Life was indeed very simple when all green-coloured algae were included in a single class, the Chlrophyceae. Increasingly, it has become clear that the green algae are very diverse in their relationships and are now included in two phyla (Chlrophyta and Charophyta) and at least 17 classes! Progress has been so rapid that text-books are out of date almost as soon as they are printed. Up-to-date numbers for each of these classes and their relationships with the Rhodophyta are given by AlgaeBase.

AlgaeBase dynamic species counts shows that there are about 4,500 species of Chlorophyta including about 550 species of Trebouxiophyceae (mostly subaerial and freshwater), 2,500 Chlorophyceae (mostly freshwater), 800 species of Bryopsidophyceae (seaweeds), 50 species of Dasycladophyceae (seaweeds), 400 Siphoncladophyceae (seaweeds), and 250 marine Ulvophyceae (seaweeds). The Charophyta is entirely freshwater and includes 3,500 species currently allocated to 5 classes.

Commercial uses: Organic beta-carotene is produced in Australia from the hypersaline (growing in high salinity water often known as brine) green alga Dunaliella salina grown in huge ponds. Carotene has been shown to be very effective in preventing some cancers, including lung cancer. Caulerpa, a marine tropical to warm-temperate genus, is very popular in aquaria. Unfortunately, this has led to the introduction of a number of Caulerpa species around the world, the best-known example being the invasive species Caulerpa taxifolia.

Chlorella, a genus of freshwater and terrestrial unicellular green alga with about 100 species, is grown like yeast in bioreactors, where it has a very rapid life history. It may be taken in the form of tablets or capsules, or added to foods such as pasta or cookies. Taken in any form, it is said improve the nutritional quality of a daily diet.

Phaeophyceae: Brown Algae - Seaweed

Phaeophyceae: Brown Algae - Seaweed
Examples of brown seaweeds are : Laminaria and Saccharina, Fucus, Sargassum muticum

Characteristics
The brown colour of these algae results from the dominance of the xanthophyll pigment fucoxanthin, which masks the other pigments, Chlorophyll a and c (there is no Chlorophyll b), beta-carotene and other xanthophylls. Food reserves are typically complex polysaccharides, sugars and higher alcohols. The principal carbohydrate reserve is laminaran, and true starch is absent (compare with the green algae). The walls are made of cellulose and alginic acid, a long-chained heteropolysaccharide.

There are no known unicellular or colonial representatives; the simplest plant form is a branched, filamentous thallus. The kelps are the largest (up to 70 m long) and perhaps the most complex brown algae, and they are the only algae known to have internal tissue differentiation into conducting tissue; there is, however, no true xylem tissue as found in the 'higher' plants.

Most brown algae have an alternation of haploid and diploid generations. The haploid thalli form isogamous, anisogamous or oogamous gametes and the diploid thalli form zoospores, generally by meiosis. The haploid (gametangial) and diploid (sporangial) thalli may be similar (isomorphic) or different (heteromorphic) in appearance, or the gametangial generation may be extremely reduced (Fucales). The brown Giant Kelp Macrocystis pyrifera (top) is harvested off the coasts of California for feeding abalone. It used to be used for alginate extraction, but this now mostly comes from Atlantic Ascophyllum nodosum and Laminaria hyperborea. Alginates, derivatives of alginic acids, are used commercially for toothpastes, soaps, ice cream, tinned meats, fabric printing, and a host of other applications. It forms a stable viscous gel in water, and its primary function in the above applications is as a binder, stabilizer, emulsifier, or moulding agent. Saccharina japonica, formerly Laminaria, and other species of the genus are grown on ropes in China, Korea and Japan for food and alginate production. Undaria pinnatifida is also cultivated in Japan, Korea and China for production of Wakame, a valuable food kelp. Small amounts are also grown in Atlantic France for the European market.


About 16,000 tonnes of Ascophyllum nodosum (above, Feamainn bhuí in Irish, referring to the yellow colour in summer) are harvested each year in Ireland, dried and milled in factories at Arramara Teo., Cill Chiaráin (Kilkerrin), Co. Galway; and some 3,000 t of the resulting seaweed meal is exported and processed in Scotland for the production of alginic acid. Laminaria hyperborea stipes (sea rods) are harvested in Norway and used to be collected in drift in Scotland and Ireland. The rods are used for the manufacture of high-grade alginates. Other brown algae are used for the extraction of agricultural sprays ('liquid seaweed extracts'). These extracts are used at low concentrations on crops and their hormone-like activities are thought to be due to betaines, cytokinenins, etc. In some areas, like the west of Ireland and Scotland, kelps and other brown algae are gathered as a fertiliser for land

Common Edible Seaweeds

Common Edible Seaweeds

Common edible seaweeds include the following:

1. Arame (Eisenia bicyclis)
2. Badderlocks (Alaria esculenta)
3. Bladderwrack (Fucus vesiculosus)
4. Carola (Callophyllis variegata)
5. Carrageen moss (Mastocarpus stellatus)
6. Channelled wrack (Pelvetia canaliculata)
7. Chlorella
8. Cochayuyo (Durvillaea antarctica)
9. Dulse (Palmaria palmata)
10. Euchema cottonii
11. Gutweed (Enteromorpha intestinalis)
12. Hijiki or Hiziki (Sargassum fusiforme)
13. Irish moss (Chondrus crispus)
14. Laver (Porphyra laciniata/Porphyra umbilicalis)
15. Limu Kala (Sargassum echinocarpum)
16. Kombu (Saccharina japonica)
17. Mozuku (Cladosiphon okamuranus)
18. Nori (various species of the red alga Porphyra)
19. Oarweed (Laminaria digitata)
20. Ogonori (Gracilaria)
21. Sugar kelp (Saccharina latissima)
22. Sea Grapes or green caviar (Caulerpa lentillifera)
23. Sea Lettuce (various species of the genus Ulva)
24. Spiral wrack (Fucus spiralis)
25. Spirulina (Arthrospira platensis and Arthrospira maxima)
26. Thongweed (Himanthalia elongata)
27. Wakame (Undaria pinnatifida)

Seaweed Nutrition and Uses

Seaweed Nutrition and Uses

Seaweed contains high levels of iodine relative to other foods. In the Philippines, Tiwi, Albay residents discovered a new pancit or noodles made from seaweed, which can be cooked into pancit canton, pancit luglug, spaghetti or carbonara and is claimed to have health benefits such as being rich in calcium, magnesium and iodine.
Polysaccharides in seaweed may be metabolized in humans through the action of bacterial gut enzymes. Research has failed to find such enzymes in North-American population, while being frequent in Japanese population.
In some parts of Asia, nori 海苔 (in Japan), zicai 紫菜 (in China), and gim 김 (in Korea), sheets of the dried red alga Porphyra are used in soups or to wrap sushi or onigiri. Chondrus crispus (commonly known as Irish moss) is another red alga used in producing various food additives, along with Kappaphycus and various gigartinoid seaweeds.
Japan consumes seven types of seaweed identified by name, and the general term for seaweed is used primarily for science and not in menus.

Edible seaweed

Edible seaweed

Edible seaweed are algae that can be eaten and used in the preparation of food. It typically contains high amounts of fiber and, contrary to land based plant foods, they contain a complete protein. They may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae.
Seaweeds are also harvested or cultivated for the extraction of alginate, agar and carrageenan, gelatinous substances collectively known as hydrocolloids or phycocolloids. Hydrocolloids have attained commercial significance, especially in food production as food additives. The food industry exploits the gelling, water-retention, emulsifying and other physical properties of these hydrocolloids.
Most edible seaweeds are marine algae as most freshwater algae are toxic. While marine algae are not toxic, some do contain acids that irritate the digestion canal, while some others can have a laxative and electrolyte balancing effect.

Seaweed Farming Culture methods

Seaweed Farming Culture methods

The earliest seaweed farming guides in the Philippines recommended cultivation of Laminaria seaweed and reef flats at approximately 1m depth at low tide . They also recommended cutting off sea grasses and removing sea urchins prior to farm construction. Seedlings are then tied to monofilament lines and strung between mangrove stakes pounded into the substrate. This off-bottom method is still one of the major methods used today.
There are new long line cultivation methods that can be used in deeper water approximately 7 m in depth. They use floating cultivation lines anchored to the bottom and are the primary methods used in the villages of North Sulawesi, Indonesia.
Cultivation of seaweed in Asia is a relatively low-technology business with a high labour requirement. There have been many attempts in various countries to introduce high technology to cultivate detached plants growth in tanks on land in order to reduce labour, but they have yet to attain commercial viability.