Algae

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For the programming language, see algae programming language.
A seaweed (Laurencia) up close: the "branches" are multicellular and only about 1 mm thick. Much smaller algae are seen growing attached to the structure extending upwards in the lower right quarter
Enlarge
A seaweed (Laurencia) up close: the "branches" are multicellular and only about 1 mm thick. Much smaller algae are seen growing attached to the structure extending upwards in the lower right quarter
Algal blooms can present problems for ecosystems and human society
Enlarge
Algal blooms can present problems for ecosystems and human society

Algae (singular alga) encompass several groups of relatively simple living aquatic organisms that capture light energy through photosynthesis, using it to convert inorganic substances into organic matter.

Although algae have been traditionally regarded as simple plants, they actually span more than one domain, including both Eukaryota and Bacteria (see Blue-green algae), as well as more than one kingdom, including plants and protists, the latter being traditionally considered more animal-like (see protozoa). Thus 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.

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, and other organ structures that characterize higher plants. They are distinguished from other protozoa in that they are photoautotrophic although this is not a hard and fast distinction as some groups contain members that are mixotrophic, deriving energy both from photosynthesis and uptake of organic carbon either by osmotrophy, myzotrophy, or phagotrophy. Some unicellular species rely entirely on external energy sources and have reduced or lost their photosynthetic apparatus.

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[1]--which is available to humans and other terrestrial 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 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. Some are used as human food or harvested for useful substances such as agar or fertilizer. The study of marine algae is called phycology or algology.

Contents

[edit] Classification

[edit] Prokaryotic algae

Traditionally the 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 [2]) 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 [3]. 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 [4].

[edit] Eukaryotic algae

All other algae are eukaryotes and conduct photosynthesis within membrane-bound structures (organelles) called chroloplasts. 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.

  1. There are three groups that have primary chloroplasts (Primoplantae or Archaeplastida):
    In these groups, the chloroplast is 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.
  2. Two other groups of algae have green chloroplasts containing chlorophyll b:
    These are surrounded by three and four membranes, respectively, and were probably retained from an ingested green alga. Those of the chlorarchniophytes contain a small nucleomorph, which is the remnant of the alga's nucleus. It has been suggested that the euglenid chloroplasts only have three membranes because they were acquired through myzocytosis rather than phagocytosis.
  3. The remaining algae all 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. These groups include:
    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 though not actual chloroplasts, which appear to have a common origin with those the dinoflagellates.

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.

[edit] Forms of algae

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:

  • Colonial - small, regular groups of motile cells
  • Capsoid - individual non-motile cells embedded in mucilage
  • Coccoid - individual non-motile cells with cell walls
  • Palmelloid - non-motile cells embedded in mucilage
  • Filamentous - a string of non-motile cells connected together, sometimes branching
  • Parenchymatous - cells forming a thallus with partial differentiation of tissues

In three lines even higher levels of organization have been reached, leading to organisms with full tissue differentiation. These are the brown algae — some of which may reach 70 m in length (kelps) — the red algae, and the green algae. 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.

[edit] Algae and symbioses

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:

  • lichens - a fungus is the host, usually with a green alga or a cyanobacterium as its symbiont. Both fungal and algal species found in lichens are capable of living independently, although habitat requirements may be greatly different from those of the lichen pair.
  • corals - algae known as zooxanthellae are symbionts with corals. Notable amongst these is the dinoflagellate Symbiodinium, found in many hard corals. The loss of Symbiodinium, or other zooxanthellae, from the host is known as coral bleaching.
  • sponges - green algae live close to the surface of some sponges, for example, breadcrumb sponge (Halichondria panicea). The alga is thus protected from predators; the sponge is provided with oxygen and sugars which can account for 50 to 80% of sponge growth in some species.[5]

[edit] Uses of algae

Seaweed is used as a fertiliser
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Seaweed is used as a fertiliser

Algae are used by humans in a great many ways. 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. Certain species are edible; the best known is Palmaria palmata (Linnaeus) O. Kuntze (Rhodymenia palmata (Linnaeus) Kuntze), common name: dulse. This is a red species which is dried and may be bought in the shops in Ireland. It is eaten raw, fresh or dried, or cooked like spinach. 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 in by people of Asian background along most of the coast from California to British Columbia. The Hawaiians and the Maoris of New Zealand also use it. Chondrus crispus, (probably confused with Mastocarpus stellatus), common name: Irish moss, is also used as "carrageen" for the stiffening of milk and dairy products, such as ice-cream. 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: dabberlocks, is used either fresh or cooked, in Greenland, Iceland, Scotland and Ireland.

[edit] Fertilizer

For centuries seaweed has been used as manure: "This kind of ore they often gather and lay in heaps where it heteth and rotteth, 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."[6] There are also commercial uses of algae as agar.

Maerl is still harvested at Falmouth (also extensively in Brittany and western Ireland) and is a popular fertiliser in these days of organic gardening; Blunden et al. (1981)[7] investigated Falmouth maerl and found that L. corallioides predominated down to 6 m and P. calcareum from 6-10 m. Chemical analysis of maerl showed that it contained 32.1% CaCO3 and 3.1% MgCO3 (dry weight).

[edit] Energy source

  • Algae can be used to make biodiesel (see algaculture), and by some estimates can produce vastly superior amounts of oil, compared to terrestrial crops grown for the same purpose. Because algae grown to produce biodiesel does not need to meet the requirements of a food crop, it is much cheaper to produce. Also it does not need fresh water or fertilizer (both of which are quite expensive).
  • Algae can be grown to produce hydrogen. In 1939 a German researcher named Hans Gaffron, while working at the University of Chicago, observed that the algae he was studying, Chlamydomonas reinhardtii (a green-algae), would sometimes switch from the production of oxygen to the production of hydrogen.[1] Gaffron never discovered the cause for this change and for many years other scientists failed in their attempts at its discovery. In the late 1990s professor Anastasios Melis a researcher at the University of California at Berkeley discovered that if the algae culture medium is deprived of sulfur it will switch from the production of oxygen (normal photosynthesis), to the production of hydrogen. He found that the enzyme responsible for this reaction is hydrogenase, but that the hydrogenase lost this function in the presence of oxygen. Melis found that depleting the amount of sulfur available to the algae interrupted its internal oxygen flow, allowing the hydrogenase an environment in which it can react, causing the algae to produce hydrogen. [2] Chlamydomonas moeweesi is also a good strain for the production of hydrogen.
  • Algae can be grown to produce biomass, which can be burned to produce heat and electricity. [3]

[edit] Pollution control

  • Algae are used in wastewater treatment facilities, reducing the need for more dangerous chemicals.
  • Algae can be used to capture fertilizers in runoff from farms. If this algae is then harvested, it itself can be used as fertilizer.
  • Algae bioreactors are used by some powerplants to reduce CO2 emissions. [4] The CO2 can be pumped into a pond, or some kind of tank, on which the algae feed. Alternatively, the bioreactor can be installed directly on top of a smokestack. This techology has been pioneered by Massachusetts-based GreenFuelTechnologies.[5].

[edit] Nutritional value of algae

  • 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[6]. 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.
  • Algae is sometimes also used as a food, as in the Chinese "vegetable" known as fat choy (which is actually a cyanobacterium).
  • 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). [7] [8]

The natural pigments produced by algae can be used as an alternative to chemical dyes and coloring agents[9]. 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.

[edit] References (general)

Guiry, M.D. and Blunden, G. (Eds) 1991. Seaweed Resources in Europe: Uses and Potential. John Wiley & Sons. ISBN 0-471929-47-6

Lembi, C.A. and Waaland, J.R. (Eds.) 1988. Algae and Human Affairs. Cambridge University Press, Cambridge. ISBN 0-521321-15-8

[edit] History of Phycology

Main article: History of phycology

[edit] Collecting and preserving specimens

  • Seaweed specimens can easily be collected and preserved. Such specimens are valuable for further research and confirmation. Well preserved specimens can be kept for two or three hundred years. Those of Carl von Linne (1707 - 1778) are still available for reference. Many species can be collected from the littoral shore down to low tide, species below low tide can be collected by diving or dredging. The whole algal specimen should be collected, that is the holdfast, stipe and lamina. If possible specimens of algae reproducing will be more useful and easied to identify.
  • When collected on the shore the specimens should be placed in a labelled specimen bag and a note made in a field note-book. This may be done by having the bags pre-numbered and the numbers used to cross reference the specimen. Details of the shore: how far down the shore, upper littoral, mid littoral or low littoral; in rock pool, deep rock pool and exposure of the shore etc should be made. A general note of the most common species in the area, seen but not collected, is valuable. Sometimes these large and supposidely common species should be collected, as it may be that although common no specimen from that area has ever been reported and further research may reveal subspecies ar varieties. This may happen in areas rarely visited. Also, there are interesting epiphytes on the stipe which would only be noticed in the laboratory and not on the shore.In the laboratory a note should be made of the name of the locality, the grid reference or longitude and latitude, details of the shore - the exposure to wave action and the dominant species noted etc. It may be helpful to collect a few of the common species as a reminder of the ecology and zone where the specimen was found.
  • The specimens may be preserved by carefully selecting a suitable individual, washing it in salt water and then floating it in a shallow pan of seawater, a photographic dish is very useful. Then slide a firm sheet of paper or card of good quality under the specimen and slowly raise it, permitting the water to flow off carrying the specimen into a natural shape with a little arrangement as necessary. Drain off the excess water and place the sheet on newspapers or blotting papers. Place a sheet of blotting paper on top of the specimen with muslin untop of the specimen. The muslin will prevent the alga sticking to the blotting paper (or newspaper). Several specimens, with blotting papers above and below, may be then pressed in a plant press or between boards with a weight above (a brick or the like will suffice). Replace the blotting paper above and below the specimen several times until the specimens are dry. This will depend on the size of the specimens, small fine specimens will dry quickly while thick specimens will take longer - perhaps a week. Specimens prepared in this manner should then be labelled, usually on the bottom right-hand corner with the name of the species, the collector, the determinor, the date, the site where collected and details of the shore as recorded. In general these specimens will stick to the paper and the salt will help preserve them from booklice or the like. In some cases the base where the holdfast is will not stick and will have to be attacked with a glue, adhesive tapes or pins. Specimens dried on paper can be affixed to pages of an album, however as it is best to never turn over an herbarium sheet and pages of an album have to be turned over the specimens may be damaged.
  • Coralline algae have often been often ignored by the casual collector and are under-recorded, they are therefore worth-while collecting. There are coralline species such as Corallina officinalis which are not encrusting and may be simply collected, washed and dried without pressing, although pressing is usual. Care must be taken as these tend to break up and fall apart and it will be necessary to enclose them in envelopes or small boxes. The "encrusting" species which grow as a crust on rock or the stipes of other algae can be chipped off the rock and allowed to dry. They may then stored in small labelled boxes as the other specimens. Tippex or other such paint-like mixture can be used as a surface on which to write a reference number and details if possible. One tip is to use different colors of tippex or coloured paint in very small dabs to distinguish different species on the one stone or rock.

[edit] Biological Exposure Scale

A useful biological exposure scale is given on pages 284 - 285 in Lewis, J.R.1964, Chapter:17. The Ecology of Rocky Shores. The English Universities Press.

[edit] Examples

Atractophora hypnoides P.L.Crouan and H.M.Crouan (red algae)

Ascophyllum nodosum

Charales (green algae)

Codium

Fucus

Ulva lactuca

Laminaria

Lemanea

Pelvetia canaliculata

Palmaria palmata

[edit] Trivia

"But who can paint Like Nature? Can imagination boast, Amidst its gay creation, hues like hers? Or can it mix them with that matchless skill, And lose them in each other, as appears In each attractive plant that sucks and swells This juicy tide, a twining mass of tubes:" - From Gifford, I. 1853. The Marine Botanist; an Introduction to the study... Brighton, London.

A student, having collected some beautiful Algae on the shore, showed the contents of his vasculum to the Professor of Botany whose lectures he attended, expressing a wish to get some information respecting them. The Professor looked at them, and putting on his spectacles, again looked at them, when, pushing them from him, he exclaimed: "Pooh! a parcel of Seaweeds, Sir; a parcel of Seaweeds!" - Landsborough, D. 1857. A Popular History of British Seaweeds. London.

Algae is also known as "Pond Scum."

"nihil vilior alga" "nothing more vile than seaweed" Virgil.

[edit] See also

[edit] Links

1. http://en.wikipedia.org/wiki/List_of_biologists

[edit] External links

 Wikimedia Commons has media related to:

[edit] References

[edit] Cited references

  1. ^ http://www.ecology.com/dr-jacks-natural-world/most-important-organism/index.html
  2. ^ http://www.ucmp.berkeley.edu/bacteria/cyanolh.html
  3. ^ Schopf, JW, and Packer, BM, Science, 1987, 237, 70
  4. ^ http://www.biologie.uni-hamburg.de/b-online/e42/42a.htm
  5. ^ http://www.uwsp.edu/cnr/UWEXlakes/laketides/vol26-4/vol26-4.pdf
  6. ^ Chapman, V.J. 1950. Seaweeds and their Uses. Methuen & Co. Ltd., London
  7. ^ Blunden, G., Farnham, W.F. Jephson, N., Barwell, C.J., Fenn, R.H. and Plunkett, B.A. 1981. The composition of maerl beds of economic interest in northern Brittany, Cornwall, and Ireland. Proceedings of the International Seaweed Symposium. 10: 651 - 656

[edit] Ecology

  • Lewis, J.R. 1964. The Ecology of Rocky Shores. The English Universities Press Ltd.

[edit] Identification

  • Abbott, I.A. and Hollenberg, G.J. 1976. Marine Algae of California. Stanford University Press, California.
  • Brodie, J.A. and Irvine, L.M. 2003. Seaweeds of the British Isles. Volume 1 Part 3B. The Natural History Museum, London.
  • Burrows, E.M. 1991. Seaweeds of the British Isles. Volume 2. British Museum (Natural History), London.
  • Christensen, T. 1987. Seaweeds of the British Isles. Volume 4. British Museum (Natural History), London.
  • Dixon, P.S. and Irvine, L.M. 1977. Seaweeds of the British Isles. Volume 1. Part 1. Introduction, Nemaliales, Gigartinales. British Museum (Natural History), London.
  • Irvine, L.M. 1983. Seaweeds of the British Isles. Volume 1, Part 2A. British Museum (Natural History), London.
  • Irvine, L.M. and Chamberlain, Y.M. 1994. Seaweeds of the British Isles. Volume 1 Part 2B. The Natural History Museum, London.
  • Fletcher, R.L. 1987. Seaweeds of the British Isles. Volume 3 Part 1. British Museum (Natural History), London.
  • John, D.M., Whitton, B.A. and Brook, J.A. (Eds.) 2002. The Freshwater Algal Flora of the British Isles. Cambridge University Press, U.K.
  • Stegenga, H., Bolton, J.J. and Anderson, R.J.1997. Seaweeds of the south African west coast. Boltus Herbarium, University of Cape Town.
  • Taylor, W.R. 1957. Marine algae of the north-eastern coasts of North America. Revised edition. University of Michigan Press. Ann Arbor.

[edit] Uses of algae

  • Mumford, T.F. and Miura, A. 1988. 4. Porphyra as food: cultivation and economics. p.87 - 117. In Lembi, C.A. and Waaland, J.R. (Ed.) Algae and Human Affairs. 1988. Cambridge University Press.
  • Guiry, M.D. and Blunden, G. (Ed.) 1991. Seaweed Resources in Europe: Uses and Potential. John Wiley and Sons Ltd.
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