Phaeophyceae: Brown Algae

Examples: Laminaria and Saccharina, Fucus, Sargassum muticum, brown seaweeds

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

There are about 1800 species of brown algae, and most are marine. In general, brown algae are larger and more species are found in colder waters. Virtually all the biomass worldwide comes from a relatively small number of species in the orders Laminariales and Fucales. The total wholesale value of dried brown algae worldwide collected in the wild or cultivated is less than $100 million dollars.

Blue-green algae

Blue-green algae, also known as cyanophytes or Cyanobacteria are photosynthetic and essentially aquatic prokaryotic organisms closely related to bacteria. They are found almost everywhere, but are most common in marine and freshwater habitats, in damp terrestrial habitats, and sometimes in association with fungi to form lichens. About 8% of lichens have the blue-green algal genus Nostoc as a partner.
Some blue-greens are actually blue-green in colour. See below for a filamentous blue-green marine species on the Cape Peninsula in South Africa. However, they can be red (the Red Sea is thought to be named for a bloom of a red blue-green planktonic species Trichodesmium erythraeum), green (often on trees), black (long black streaks on buildings, often very unsightly), and just about any colour in the spectrum

Individual blue-green algal cells are quite small and may be unicellular, but they are most commonly filamentous (lines of cells placed end to end) and they often are in colonies large enough to see. They have the distinction of being the oldest known fossils, more than 3.5 billion years old, in fact. It may surprise you then to know that the cyanobacteria are still ver much around; they are one of the largest and most important groups of bacteria on earth.
Blue green algae are very important intertidal organisms on tropical and subtropical reefs. Below are black patches of Lyngbya majuscula on Lord Howe Island, off Australia's east coast. This species can bloom to form huge floating masses in various parts of the world.

Many Proterozoic oil deposits are thought to be due to the proliferation of cyanobacteria. Blue-green algae fix atmospheric nitrogen and they are also important providers of nitrogenous fertilizer in the cultivation of rice and beans. Blue-green algae have been tremendously important in shaping the course of evolution and ecological change throughout earth's history. The oxygen atmosphere that we depend on was probably generated by numerous cyanobacteria during the Archaean and Proterozoic Eras. Before that time, the atmosphere had a very different chemistry, quite unsuited to life as we know it today.
The other great contribution of the cyanobacteria is the origin of plants. The chloroplast with which plants make food for themselves is actually a cyanobacterium living within the plant's cells. Sometime in the late Proterozoic, or in the early Cambrian, cyanobacteria began to take up residence other cells, making food for the host in return for a home. This event is one example of endosymbiosis, and s similar process was also the origin of the eukaryotic mitochondrion.
Many blue-green algae produce toxins that can be dangerous to humans and to animals. Because they bloom in freshwater and marine habitats, they may cause mass mortalities of fish and other animals.

What are algae?

Algae are pond scums, terrestrial algae, snow algae, seaweeds, freshwater and marine phytoplankton. The plant body is relatively undifferentiated, and there are no true roots and leaves.

Pronunciation: Algae ("al'jay" or "al'gay", both are used today) is the plural; Alga ("al'ga") is the singular, but here is no such thing as "algaes".

Algae are very simple chlorophyll-containing organisms: some say that they are plants; other say that the are not, calling them protists or protoctists. According to the most recent phylogenetic studies, both are not quite correct. Some algae (most greens and the reds) are indeed related to the land plants, and some flagellated algae are related to the protists, but there is no justification for the including all algae in any generic term other than "algae".
We use the term "algae" very loosely, simply because coralling them is so very difficult. As conceived in the broadest sense, algae are oxygen-generating, photosynthetic organisms other than embryophyte land plants, fungi and lichens. Quite simply, they are an artificial and highly heterogeneous aggregation of organisms belonging to many different evolutionary lineages, and therefore highly diverse from a genetic point of view. This genetic diversity is reflected in the enormous diversity exhibited by algae in terms of morphological, ultrastructural, ecological, biochemical, and physiological traits.

Marine macroalgae, or seaweeds, are plant-like organisms that generally live
attached to rock or other hard substrata in coastal areas. They belong to three
different groups, empirically distinguished since the mid-nineteenth century by the Irish botanist William Henry Harvey (1811-1866) on the basis of thallus color: red algae (phylum Rhodophyta), brown algae (phylum Ochrophyta, class Phaeophyceae), and green algae (phylum Chlorophyta, classes Bryopsidophyceae, Chlorophyceae, Dasycladophyceae, Prasinophyceae, and Ulvophyceae). Distinguishing these three groups, however, involves more substantial differences than indicated by this simple designation. In addition to the pigmentation, they differ considerably in many ultrastructural and biochemical features including photosynthetic pigments, storage compounds, composition of cell walls, presence/absence of flagella, ultrastructure of mitosis, connections between adjacent cells, and the fine structure of the chloroplasts. In general, we can say that they are simple organisms composed of one cell, or grouped together in colonies, or as organisms with many cells, sometimes collaborating together as simple tissues.
Most algae form some sort of spore, which is a cell that is often motile and serves to reproduce the organism. Some are colonial and motile in the adult phase like Volvox (right, photograph © Karl Bruun). Algae also have sex, often a very simple kind of sex where the algae themselves act as gametes, but sometimes very complicated with egg and sperm-like cells. In all probability an alga was the first organism to have something that we would recognise as sex, about 1.5 billion years ago.
Some of the larger kelps have translocation but most do not. They have no need for water-conducting tissues as they are, at some stage, surrounded by water. They reproduce by spores of some kind. There are no seeds. Spores may be motile or non-motile; varies Karlphylum to phylum, e.g., the red and blue-green algae are non-flagellated.
Algae of one kind or another have been around for more than 2 billion years. We are still discovering new algae, sometimes whole groups of them at a time.
Algae of other groups usually have two flagella (singular: flagellum). Reproduction may be isogamous, anisogamous, or oogamous. Female gametangia are not enclosed by a wall of sterile cells as in higher cryptogams. Mostly autotrophic (photosynthetic), pigments very variable and are the basis of classification; all have chlorophyll a; some have b, others c; all have accessory pigments of some kind e.g. phycocyanin (blueish), phycoerythrin (reddish), carotenes (yellow-brown), xanthophylls (brown).
Some are heterotrophic (get energy from non-photosynthetic sources also). Great variation in size - unicellular and 3-10 µm (microns) to giant kelps up to 70 meters long and growing at up to 50 cm per day. Found in mostly aquatic situations (need water to reproduce and, generally, to photosynthesise).
Where are algae found? Algae are found just about everywhere on earth: in the sea, in our rivers and lakes, on soils and walls, in animals and plants (as symbionts - partners collaborating together); in fact just about everywhere where there is light with which to photosynthesise.
There are about 40,000 species of algae: up to date numbers and the numbers for each phylum are provided dynamically by AlgaeBase.

Green algae

Chlorophyta: Green Algae

Examples: Chlorella, Chlamydomonas, Spirogyra, Ulva. Green seaweeds.
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. According to the Taiwan Chlorella Manufacturing Company the increase in processed and refined foods in the diet of modern man make Chlorella an important food supplement for anyone interested in better health.
Back to index page.

JUST PUBLISHED

Advertising

Acadian Seaplants is a diversified, technology-based manufacturer of natural, specialty fertilizers, feed, food, food ingredients and brewery supplies derived from select species of marine plants. Link.

Koeltz Scientific Books has the largest holdings of seaweed and algal books in the world. Search their on-line database.
Irish Seaweeds Ltd. Suppliers of 100% natural hand-harvested seaweeds and edible sea vegetable products from Ireland. Link.