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I've been farming freshwater fishes. After some time, i found some green algae grows there. When the algae dried, it looks like nori (which commonly used for sushi wrapping).
So, i wonder if those algae edible for human. Are the algae safe to eat?
Here's the picture:
I came across a this Wikipedia page which said blue green algae from ponds can be used as dietary supplement (in tablet form).
Many other articles on the internet like here suggest it is included in many diets in many places across the globe.
However, without proper regulation one can include a heavy metal contaminated vegetable to their diet which is detrimental to health. Furthermore cyanobacteria are known to produce toxic substances known as microcystins which can cause damage to human organs as well.
So unless you are certain of the biochemical balance of your pond I would recommend not integrating it in your diet. Rather you can find commercially available ones which your local regulatory authority(s) recommend for dietary purposes.
First off: Don't risk it
I'm not an ecologist but I believe the type of algae you are holding tends to be cyanobacteria.
Cyanobacteria make all kinds of toxins, check the first table in this article.
Some cyanobacteria are eaten like Arthospira (commonly called spirulina) but I would not eat any random filamentous cyanobacteria. They also tend to be quite hard to digest so at best you will have increased your dietary fibre level and at worst… well make sure your sanitary facilities have enough capacity.
The Next Big Superfood Could Be Green And Slimy
For others, it spells promise. "Imagine our future living in cities where buildings are covered with photosynthetic membranes and vertical gardens, collecting the sun's energy and producing food and bioproducts for urban citizens," wrote CEO of Smart Microfarms Robert Henrikson in AlgaeIndustryMagazine.com.
While we aren't erecting edible green skyscrapers yet, the tiny organisms called microalgae that would power them are about to have their heyday.
Most know microalgae as a potential biofuel source, the most active field of algae research. However, it may be "one of the most nutritious foods known to man," according to some researchers, perhaps making the green plant one of the world's most overlooked foods.
The simple green organisms guided ancient cultures through famine and are now making their way into everything from animal feed to baby formula.
Quest for Edible Malarial Vaccine Leads to Other Potential Medical Uses for Algae
Can scientists rid malaria from the Third World by simply feeding algae genetically engineered with a vaccine?
The scientists used a protein produced by the bacterium responsible for cholera, Vibrio cholera, that binds to intestinal epithelial cells.
That’s the question biologists at UC San Diego sought to answer after they demonstrated last May that algae can be engineered to produce a vaccine that blocks malaria transmission. In a follow up study, published online today in the scientific journal Applied and Environmental Microbiology, they got their answer: Not yet, although the same method may work as a vaccine against a wide variety of viral and bacterial infections.
In their most recent study, which the authors made freely available on the Applied and Environmental Microbiology website at http://aem.asm.org, the researchers fused a protein that elicits an antibody response in mice against the organism that causes malaria, Plasmodium falciparum, which afflicts 225 million people worldwide, with a protein produced by the bacterium responsible for cholera, Vibrio cholera, that binds to intestinal epithelial cells. They then genetically engineered algae to produce this two-protein combination, or “fusion protein,” freeze dried the algae and later fed the resulting green powder to mice. The researchers hypothesized that together these proteins might be an effective oral vaccine candidate when delivered using algae. The result? The mice developed Immunoglobulin A (IgA) antibodies to both the malarial parasite protein and to a toxin produced by the cholera bacteria. Because IgA antibodies are produced in the gut and mucosal linings, they don’t protect against the malarial parasites, which are injected directly into the bloodstream by mosquitoes. But their study suggests that similar fusion proteins might protect against infectious diseases that affect mucosal linings using their edible freeze-dried algae.
Mosquitoes from the genus Anopheles transmit the protozoan that causes malaria.
“Many bacterial and viral infections are caused by eating tainted food or water,” says Stephen Mayfield, a professor of biology at UC San Diego who headed the study. “So what this study shows is that you can get a really good immune response from a recombinant protein in algae that you feed to a mammal. In this case, it happens to be a mouse, but presumably it would also work in a human. That’s really encouraging for the potential for algae-based vaccines in the future.” The scientists say bacterial infections caused by Salmonella, E. coli and other food and water-borne pathogens could be prevented in the future with inexpensive vaccines developed from algae that could be eaten rather than injected. “It might even be used to protect against cholera itself,” said James Gregory, a postdoctoral researcher in Mayfield’s lab and the first author of the paper. In his experiments with mice, he said, Immunoglobulin G (IgG) antibodies–which are found in blood and tissues–were produced against the cholera toxin, “but not the malaria antigen and we don’t quite understand why.” Part of the difficulty in creating a vaccine against malaria is that it requires a system that can produce structurally complex proteins that resemble those made by the parasite, thus eliciting antibodies that disrupt malaria transmission. Most vaccines created by engineered bacteria are relatively simple proteins that stimulate the body’s immune system to produce antibodies against bacterial invaders. Three years ago, a UC San Diego team of biologists headed by Mayfield, who is also the director of the San Diego Center for Algae Biotechnology, a research consortium seeking to develop transportation fuels from algae, published a landmark study demonstrating that many complex human therapeutic proteins, such as monoclonal antibodies and growth hormones, could be produced by the common algae Chlamydomonas. That got Gregory wondering if complex malarial transmission blocking vaccine candidates could also be produced by Chlamydomonas. Two billion people live in malaria endemic regions, making the delivery of a malarial vaccine a costly and logistically difficult proposition, especially when that vaccine is expensive to produce. So the UC San Diego biologists set out to determine if this alga, an organism that can produce complex proteins very cheaply, could produce malaria proteins that would inhibit infections from malaria.
The edible algae Chlamydomonas, seen here at UC San Diego, can be grown in ponds anywhere in the world.
“It’s too costly to vaccinate two billion people using current technologies,” explained Mayfield. “Realistically, the only way a malaria vaccine will ever be used in the developing world is if it can be produced at a fraction of the cost of current vaccines. Algae have this potential because you can grow algae any place on the planet in ponds or even in bathtubs.” Collaborating with Joseph Vinetz, a professor of medicine at UC San Diego and a leading expert in tropical diseases who has been working on developing vaccines against malaria, the researchers showed in their earlier study, published in the open access journal PLoS ONE last May that the proteins produced by the algae, when injected into laboratory mice, made antibodies that blocked malaria transmission from mosquitoes. The next step was to see if they could immunize mice against malaria by simply feeding the genetically engineered algae. “We think getting oral vaccines in which you don’t have to purify the protein is the only way in which you can make medicines dramatically cheaper and make them available to the developing world,” says Mayfield. “The Holy Grail is to develop an orally delivered vaccine, and we predict that we may be able to do it in algae, and for about a penny a dose. Our algae-produced malarial vaccine works against malarial parasites in mice, but it needs to be injected into the bloodstream.” Although an edible malarial vaccine is not yet a reality, he adds, “this study shows that you can make a pretty fancy protein using algae, deliver it to the gut and get IgA antibodies that recognize that protein. Now we know we have a system that can deliver a complex protein to the right place and develop an immune response to provide protection.” Mayfield is also co-director of the Center for Food & Fuel for the 21st Century, a new research unit that has brought together researchers from across the campus to develop renewable ways of improving the nation’s food, fuel, pharmaceutical and other bio-based industries and is this week hosting a major symposium on the subject at the Institute of the Americas at UC San Diego. Two other researchers in Mayfield’s laboratory, Aaron Topol and David Doerner, participated in the research study, which was supported by grants from the San Diego Foundation, the California Energy Commission (500-10-039) and the National Science Foundation (CBET-1160184).
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The singular alga is the Latin word for 'seaweed' and retains that meaning in English.  The etymology is obscure. Although some speculate that it is related to Latin algēre, 'be cold',  no reason is known to associate seaweed with temperature. A more likely source is alliga, 'binding, entwining'. 
The Ancient Greek word for 'seaweed' was φῦκος (phŷkos), which could mean either the seaweed (probably red algae) or a red dye derived from it. The Latinization, fūcus, meant primarily the cosmetic rouge. The etymology is uncertain, but a strong candidate has long been some word related to the Biblical פוך (pūk), 'paint' (if not that word itself), a cosmetic eye-shadow used by the ancient Egyptians and other inhabitants of the eastern Mediterranean. It could be any color: black, red, green, or blue. 
Accordingly, the modern study of marine and freshwater algae is called either phycology or algology, depending on whether the Greek or Latin root is used. The name fucus appears in a number of taxa.
The committee on the International Code of Botanical Nomenclature has recommended certain suffixes for use in the classification of algae. These are -phyta for division, -phyceae for class, -phycideae for subclass, -ales for order, -inales for suborder, -aceae for family, -oidease for subfamily, a Greek-based name for genus, and a Latin-based name for species.
Algal characteristics basic to primary classification Edit
The primary classification of algae is based on certain morphological features. The chief among these are (a) pigment constitution of the cell, (b) chemical nature of stored food materials, (c) kind, number, point of insertion and relative length of the flagella on the motile cell, (d) chemical composition of cell wall and (e) presence or absence of a definitely organized nucleus in the cell or any other significant details of cell structure.
History of classification of algae Edit
Although Carolus Linnaeus (1754) included algae along with lichens in his 25th class Cryptogamia, he did not elaborate further on the classification of algae.
Jean Pierre Étienne Vaucher (1803) was perhaps the first to propose a system of classification of algae, and he recognized three groups, Conferves, Ulves, and Tremelles. While Johann Heinrich Friedrich Link (1820) classified algae on the basis of the colour of the pigment and structure, William Henry Harvey (1836) proposed a system of classification on the basis of the habitat and the pigment. J. G. Agardh (1849–1898) divided algae into six orders: Diatomaceae, Nostochineae, Confervoideae, Ulvaceae, Floriadeae and Fucoideae. Around 1880, algae along with fungi were grouped under Thallophyta, a division created by Eichler (1836). Encouraged by this, Adolf Engler and Karl A. E. Prantl (1912) proposed a revised scheme of classification of algae and included fungi in algae as they were of opinion that fungi have been derived from algae. The scheme proposed by Engler and Prantl is summarised as follows: 
- Eumycetes (Fungi)
The algae contain chloroplasts that are similar in structure to cyanobacteria. Chloroplasts contain circular DNA like that in cyanobacteria and are interpreted as representing reduced endosymbiotic cyanobacteria. However, the exact origin of the chloroplasts is different among separate lineages of algae, reflecting their acquisition during different endosymbiotic events. The table below describes the composition of the three major groups of algae. Their lineage relationships are shown in the figure in the upper right. Many of these groups contain some members that are no longer photosynthetic. Some retain plastids, but not chloroplasts, while others have lost plastids entirely.
Phylogeny based on plastid  not nucleocytoplasmic genealogy:
These groups have green chloroplasts containing chlorophylls a and b.  Their chloroplasts are surrounded by four and three membranes, respectively, and were probably retained from ingested green algae.
Chlorarachniophytes, which belong to the phylum Cercozoa, contain a small nucleomorph, which is a relict of the algae's nucleus.
Euglenids, which belong to the phylum Euglenozoa, live primarily in fresh water and have chloroplasts with only three membranes. The endosymbiotic green algae may have been acquired through myzocytosis rather than phagocytosis. 
These groups have chloroplasts containing chlorophylls a and c, and phycobilins. The shape varies from plant to plant they may be of discoid, plate-like, reticulate, cup-shaped, spiral, or ribbon shaped. They have one or more pyrenoids to preserve protein and starch. The latter chlorophyll type is not known from any prokaryotes or primary chloroplasts, but genetic similarities with 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, although other evidence casts doubt on whether the heterokonts, Haptophyta, and cryptomonads are in fact more closely related to each other than to other groups.  
The typical dinoflagellate chloroplast has three membranes, but considerable diversity exists in chloroplasts within the group, and a number of endosymbiotic events apparently occurred.  The Apicomplexa, a group of closely related parasites, also have plastids called apicoplasts, which are not photosynthetic, but appear to have a common origin with dinoflagellate chloroplasts. 
Linnaeus, in Species Plantarum (1753),  the starting point for modern botanical nomenclature, recognized 14 genera of algae, of which only four are currently considered among algae.  In Systema Naturae, Linnaeus described the genera Volvox and Corallina, and a species of Acetabularia (as Madrepora), among the animals.
In 1768, Samuel Gottlieb Gmelin (1744–1774) published the Historia Fucorum, the first work dedicated to marine algae and the first book on marine biology to use the then new binomial nomenclature of Linnaeus. It included elaborate illustrations of seaweed and marine algae on folded leaves.  
W. H. Harvey (1811–1866) and Lamouroux (1813)  were the first to divide macroscopic algae into four divisions based on their pigmentation. This is the first use of a biochemical criterion in plant systematics. Harvey's four divisions are: red algae (Rhodospermae), brown algae (Melanospermae), green algae (Chlorospermae), and Diatomaceae.  
At this time, microscopic algae were discovered and reported by a different group of workers (e.g., O. F. Müller and Ehrenberg) studying the Infusoria (microscopic organisms). Unlike macroalgae, which were clearly viewed as plants, microalgae were frequently considered animals because they are often motile.  Even the nonmotile (coccoid) microalgae were sometimes merely seen as stages of the lifecycle of plants, macroalgae, or animals.  
Although used as a taxonomic category in some pre-Darwinian classifications, e.g., Linnaeus (1753), de Jussieu (1789), Horaninow (1843), Agassiz (1859), Wilson & Cassin (1864), in further classifications, the "algae" are seen as an artificial, polyphyletic group.
Throughout the 20th century, most classifications treated the following groups as divisions or classes of algae: cyanophytes, rhodophytes, chrysophytes, xanthophytes, bacillariophytes, phaeophytes, pyrrhophytes (cryptophytes and dinophytes), euglenophytes, and chlorophytes. Later, many new groups were discovered (e.g., Bolidophyceae), and others were splintered from older groups: charophytes and glaucophytes (from chlorophytes), many heterokontophytes (e.g., synurophytes from chrysophytes, or eustigmatophytes from xanthophytes), haptophytes (from chrysophytes), and chlorarachniophytes (from xanthophytes).
With the abandonment of plant-animal dichotomous classification, most groups of algae (sometimes all) were included in Protista, later also abandoned in favour of Eukaryota. However, as a legacy of the older plant life scheme, some groups that were also treated as protozoans in the past still have duplicated classifications (see ambiregnal protists).
Some parasitic algae (e.g., the green algae Prototheca and Helicosporidium, parasites of metazoans, or Cephaleuros, parasites of plants) were originally classified as fungi, sporozoans, or protistans of incertae sedis,  while others (e.g., the green algae Phyllosiphon and Rhodochytrium, parasites of plants, or the red algae Pterocladiophila and Gelidiocolax mammillatus, parasites of other red algae, or the dinoflagellates Oodinium, parasites of fish) had their relationship with algae conjectured early. In other cases, some groups were originally characterized as parasitic algae (e.g., Chlorochytrium), but later were seen as endophytic algae.  Some filamentous bacteria (e.g., Beggiatoa) were originally seen as algae. Furthermore, groups like the apicomplexans are also parasites derived from ancestors that possessed plastids, but are not included in any group traditionally seen as algae.
The first land plants probably evolved from shallow freshwater charophyte algae much like Chara almost 500 million years ago. These probably had an isomorphic alternation of generations and were probably filamentous. Fossils of isolated land plant spores suggest land plants may have been around as long as 475 million years ago.  
A range of algal morphologies is exhibited, and convergence of features in unrelated groups is common. The only groups to exhibit three-dimensional multicellular thalli are the reds and browns, and some chlorophytes.  Apical growth is constrained to subsets of these groups: the florideophyte reds, various browns, and the charophytes.  The form of charophytes is quite different from those of reds and browns, because they have distinct nodes, separated by internode 'stems' whorls of branches reminiscent of the horsetails occur at the nodes.  Conceptacles are another polyphyletic trait they appear in the coralline algae and the Hildenbrandiales, as well as the browns. 
Most of the simpler algae are unicellular flagellates or amoeboids, but colonial and nonmotile 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 lifecycle of a species, are
- : small, regular groups of motile cells
- Capsoid: individual non-motile cells embedded in mucilage
- Coccoid: individual non-motile cells with cell walls
- Palmelloid: nonmotile cells embedded in mucilage
- Filamentous: a string of nonmotile 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, with full tissue differentiation. These are the brown algae,  —some of which may reach 50 m in length (kelps)  —the red algae,  and the green algae.  The most complex forms are found among the charophyte algae (see Charales and Charophyta), in a lineage that eventually led to the higher land plants. The innovation that defines these nonalgal plants is the presence of female reproductive organs with protective cell layers that protect the zygote and developing embryo. Hence, the land plants are referred to as the Embryophytes.
The term algal turf is commonly used but poorly defined. Algal turfs are thick, carpet-like beds of seaweed that retain sediment and compete with foundation species like corals and kelps, and they are usually less than 15 cm tall. Such a turf may consist of one or more species, and will generally cover an area in the order of a square metre or more. Some common characteristics are listed: 
- Algae that form aggregations that have been described as turfs include diatoms, cyanobacteria, chlorophytes, phaeophytes and rhodophytes. Turfs are often composed of numerous species at a wide range of spatial scales, but monospecific turfs are frequently reported. 
- Turfs can be morphologically highly variable over geographic scales and even within species on local scales and can be difficult to identify in terms of the constituent species. 
- Turfs have been defined as short algae, but this has been used to describe height ranges from less than 0.5 cm to more than 10 cm. In some regions, the descriptions approached heights which might be described as canopies (20 to 30 cm). 
Many algae, particularly members of the Characeae species,  have served as model experimental organisms to understand the mechanisms of the water permeability of membranes, osmoregulation, turgor regulation, [ clarification needed ] salt tolerance, cytoplasmic streaming, and the generation of action potentials.
Phytohormones are found not only in higher plants, but in algae, too. 
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 are:
Lichens are defined by the International Association for Lichenology to be "an association of a fungus and a photosynthetic symbiont resulting in a stable vegetative body having a specific structure".  The fungi, or mycobionts, are mainly from the Ascomycota with a few from the Basidiomycota. In nature they do not occur separate from lichens. It is unknown when they began to associate.  One mycobiont associates with the same phycobiont species, rarely two, from the green algae, except that alternatively, the mycobiont may associate with a species of cyanobacteria (hence "photobiont" is the more accurate term). A photobiont may be associated with many different mycobionts or may live independently accordingly, lichens are named and classified as fungal species.  The association is termed a morphogenesis because the lichen has a form and capabilities not possessed by the symbiont species alone (they can be experimentally isolated). The photobiont possibly triggers otherwise latent genes in the mycobiont. 
Trentepohlia is an example of a common green alga genus worldwide that can grow on its own or be lichenised. Lichen thus share some of the habitat and often similar appearance with specialized species of algae (aerophytes) growing on exposed surfaces such as tree trunks and rocks and sometimes discoloring them.
Coral reefs Edit
Coral reefs are accumulated from the calcareous exoskeletons of marine invertebrates of the order Scleractinia (stony corals). These animals metabolize sugar and oxygen to obtain energy for their cell-building processes, including secretion of the exoskeleton, with water and carbon dioxide as byproducts. Dinoflagellates (algal protists) are often endosymbionts in the cells of the coral-forming marine invertebrates, where they accelerate host-cell metabolism by generating sugar and oxygen immediately available through photosynthesis using incident light and the carbon dioxide produced by the host. Reef-building stony corals (hermatypic corals) require endosymbiotic algae from the genus Symbiodinium to be in a healthy condition.  The loss of Symbiodinium from the host is known as coral bleaching, a condition which leads to the deterioration of a reef.
Sea sponges Edit
Endosymbiontic green algae live close to the surface of some sponges, for example, breadcrumb sponges (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. 
Rhodophyta, Chlorophyta, and Heterokontophyta, the three main algal divisions, have lifecycles which show considerable variation and complexity. In general, an asexual phase exists 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 permits efficient population increases, but less variation is possible. Commonly, in sexual reproduction of unicellular and colonial algae, two specialized, sexually compatible, haploid gametes make physical contact and fuse to form a zygote. To ensure a successful mating, the development and release of gametes is highly synchronized and regulated pheromones may play a key role in these processes.  Sexual reproduction allows for more variation and provides the benefit of efficient recombinational repair of DNA damages during meiosis, a key stage of the sexual cycle. [ citation needed ] However, sexual reproduction is more costly than asexual reproduction.  Meiosis has been shown to occur in many different species of algae. 
The Algal Collection of the US National Herbarium (located in the National Museum of Natural History) consists of approximately 320,500 dried specimens, which, although not exhaustive (no exhaustive collection exists), gives an idea of the order of magnitude of the number of algal species (that number remains unknown).  Estimates vary widely. For example, according to one standard textbook,  in the British Isles the UK Biodiversity Steering Group Report estimated there to be 20,000 algal species in the UK. Another checklist reports only about 5,000 species. Regarding the difference of about 15,000 species, the text concludes: "It will require many detailed field surveys before it is possible to provide a reliable estimate of the total number of species . "
Regional and group estimates have been made, as well:
- 5,000–5,500 species of red algae worldwide
- "some 1,300 in Australian Seas" 
- 400 seaweed species for the western coastline of South Africa,  and 212 species from the coast of KwaZulu-Natal.  Some of these are duplicates, as the range extends across both coasts, and the total recorded is probably about 500 species. Most of these are listed in List of seaweeds of South Africa. These exclude phytoplankton and crustose corallines.
- 669 marine species from California (US) 
- 642 in the check-list of Britain and Ireland 
and so on, but lacking any scientific basis or reliable sources, these numbers have no more credibility than the British ones mentioned above. Most estimates also omit microscopic algae, such as phytoplankton.
The most recent estimate suggests 72,500 algal species worldwide. 
The distribution of algal species has been fairly well studied since the founding of phytogeography in the mid-19th century.  Algae spread mainly by the dispersal of spores analogously to the dispersal of Plantae by seeds and spores. This dispersal can be accomplished by air, water, or other organisms. Due to this, spores can be found in a variety of environments: fresh and marine waters, air, soil, and in or on other organisms.  Whether a spore is to grow into an organism depends on the combination of the species and the environmental conditions where the spore lands.
The spores of freshwater algae are dispersed mainly by running water and wind, as well as by living carriers.  However, not all bodies of water can carry all species of algae, as the chemical composition of certain water bodies limits the algae that can survive within them.  Marine spores are often spread by ocean currents. Ocean water presents many vastly different habitats based on temperature and nutrient availability, resulting in phytogeographic zones, regions, and provinces. 
To some degree, the distribution of algae is subject to floristic discontinuities caused by geographical features, such as Antarctica, long distances of ocean or general land masses. It is, therefore, possible to identify species occurring by locality, such as "Pacific algae" or "North Sea algae". When they occur out of their localities, hypothesizing a transport mechanism is usually possible, such as the hulls of ships. For example, Ulva reticulata and U. fasciata travelled from the mainland to Hawaii in this manner.
Mapping is possible for select species only: "there are many valid examples of confined distribution patterns."  For example, Clathromorphum is an arctic genus and is not mapped far south of there.  However, scientists regard the overall data as insufficient due to the "difficulties of undertaking such studies." 
Algae are prominent in bodies of water, common in terrestrial environments, and are found in unusual environments, such as on snow and ice. Seaweeds grow mostly in shallow marine waters, under 100 m (330 ft) deep however, some such as Navicula pennata have been recorded to a depth of 360 m (1,180 ft).  A type of algae, Ancylonema nordenskioeldii, was found in Greenland in areas known as the 'Dark Zone', which caused an increase in the rate of melting ice sheet.  Same algae was found in the Italian Alps, after pink ice appeared on parts of the Presena glacier. 
The various sorts of algae play significant roles in aquatic ecology. Microscopic forms that live suspended in the water column (phytoplankton) provide the food base for most marine food chains. In very high densities (algal blooms), these algae may discolor the water and outcompete, poison, or asphyxiate other life forms.
Algae can be used as indicator organisms to monitor pollution in various aquatic systems.  In many cases, algal metabolism is sensitive to various pollutants. Due to this, the species composition of algal populations may shift in the presence of chemical pollutants.  To detect these changes, algae can be sampled from the environment and maintained in laboratories with relative ease. 
In classical Chinese, the word 藻 is used both for "algae" and (in the modest tradition of the imperial scholars) for "literary talent". The third island in Kunming Lake beside the Summer Palace in Beijing is known as the Zaojian Tang Dao, which thus simultaneously means "Island of the Algae-Viewing Hall" and "Island of the Hall for Reflecting on Literary Talent".
Algaculture is a form of aquaculture involving the farming of species of algae.
The majority of algae that are intentionally cultivated fall into the category of microalgae (also referred to as phytoplankton, microphytes, or planktonic algae). Macroalgae, commonly known as seaweed, also have many commercial and industrial uses, but due to their size and the specific requirements of the environment in which they need to grow, they do not lend themselves as readily to cultivation (this may change, however, with the advent of newer seaweed cultivators, which are basically algae scrubbers using upflowing air bubbles in small containers).
Commercial and industrial algae cultivation has numerous uses, including production of food ingredients such as omega-3 fatty acids or natural food colorants and dyes, food, fertilizer, bioplastics, chemical feedstock (raw material), pharmaceuticals, and algal fuel, and can also be used as a means of pollution control.
Global production of farmed aquatic plants, overwhelmingly dominated by seaweeds, grew in output volume from 13.5 million tonnes in 1995 to just over 30 million tonnes in 2016. 
Seaweed farming Edit
Seaweed farming or kelp farming is the practice of cultivating and harvesting seaweed. In its simplest form, it consists of the management of naturally found batches. In its most advanced form, it consists of fully controlling the life cycle of the algae.
The top seven most cultivated seaweed taxa are Eucheuma spp., Kappaphycus alvarezii, Gracilaria spp., Saccharina japonica, Undaria pinnatifida, Pyropia spp., and Sargassum fusiforme. Eucheuma and K. alvarezii are farmed for carrageenan (a gelling agent) Gracilaria is farmed for agar while the rest are farmed for food. The largest seaweed-producing countries are China, Indonesia, and the Philippines. Other notable producers include South Korea, North Korea, Japan, Malaysia, and Zanzibar (Tanzania).  Seaweed farming has frequently been developed as an alternative to improve economic conditions and to reduce fishing pressure and overexploited fisheries. 
Global production of farmed aquatic plants, overwhelmingly dominated by seaweeds, grew in output volume from 13.5 million tonnes in 1995 to just over 30 million tonnes in 2016.  As of 2014, seaweed was 27% of all marine aquaculture.  Seaweed farming is a carbon negative crop, with a high potential for climate change mitigation .  The IPCC Special Report on the Ocean and Cryosphere in a Changing Climate recommends "further research attention" as a mitigation tactic. 
An algae bioreactor is used for cultivating micro or macro algae. Algae may be cultivated for the purposes of biomass production (as in a seaweed cultivator), wastewater treatment, CO2 fixation, or aquarium/pond filtration in the form of an algae scrubber. Algae bioreactors vary widely in design, falling broadly into two categories: open reactors and enclosed reactors. Open reactors are exposed to the atmosphere while enclosed reactors, also commonly called photobioreactors, are isolated to varying extent from the atmosphere. Specifically, algae bioreactors can be used to produce fuels such as biodiesel and bioethanol, to generate animal feed, or to reduce pollutants such as NOx and CO2 in flue gases of power plants. Fundamentally, this kind of bioreactor is based on the photosynthetic reaction which is performed by the chlorophyll-containing algae itself using dissolved carbon dioxide and sunlight energy. The carbon dioxide is dispersed into the reactor fluid to make it accessible for the algae. The bioreactor has to be made out of transparent material.
The algae are photoautotroph organisms which perform oxygenic photosynthesis.
The equation for photosynthesis:
Agar, a gelatinous substance derived from red algae, has a number of commercial uses.  It is a good medium on which to grow bacteria and fungi, as most microorganisms cannot digest agar.
Alginic acid, or alginate, is extracted from brown algae. Its uses range from gelling agents in food, to medical dressings. Alginic acid also has been used in the field of biotechnology as a biocompatible medium for cell encapsulation and cell immobilization. Molecular cuisine is also a user of the substance for its gelling properties, by which it becomes a delivery vehicle for flavours.
Between 100,000 and 170,000 wet tons of Macrocystis are harvested annually in New Mexico for alginate extraction and abalone feed.  
Energy source Edit
To be competitive and independent from fluctuating support from (local) policy on the long run, biofuels should equal or beat the cost level of fossil fuels. Here, algae-based fuels hold great promise,   directly related to the potential to produce more biomass per unit area in a year than any other form of biomass. The break-even point for algae-based biofuels is estimated to occur by 2025. 
For centuries, seaweed has been used as a fertilizer George Owen of Henllys writing in the 16th century referring to drift weed in South Wales: 
This kind of ore they often gather and lay on great heapes, where it heteth and rotteth, and will have a strong and loathsome smell when being so rotten they cast on the land, as they do their muck, and thereof springeth good corn, especially barley . After spring-tydes or great rigs of the sea, they fetch it in sacks on horse backes, and carie the same three, four, or five miles, and cast it on the lande, which doth very much better the ground for corn and grass.
Today, algae are used by humans in many ways for example, as fertilizers, soil conditioners, and livestock feed.  Aquatic and microscopic species are cultured in clear tanks or ponds and are 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.
Naturally growing seaweeds are an important source of food, especially in Asia, leading some to label them as superfoods.  They provide many vitamins including: A, B1, B2, B6, niacin, and C, and are rich in iodine, potassium, iron, magnesium, and calcium.  In addition, commercially cultivated microalgae, including both algae and cyanobacteria, are marketed as nutritional supplements, such as spirulina,  Chlorella and the vitamin-C supplement from Dunaliella, high in beta-carotene.
Algae are national foods of many nations: China consumes more than 70 species, including fat choy, a cyanobacterium considered a vegetable Japan, over 20 species such as nori and aonori  Ireland, dulse Chile, cochayuyo.  Laver is used to make laver bread in Wales, where it is known as bara lawr in Korea, gim. It is also used along the west coast of North America from California to British Columbia, in Hawaii and by the Māori of New Zealand. Sea lettuce and badderlocks are salad ingredients in Scotland, Ireland, Greenland, and Iceland. Algae is being considered a potential solution for world hunger problem.   
Two popular forms of algae are used in cuisine:
- Chlorella: This form of alga is found in freshwater and contains photosynthetic pigments in its chloroplast. It is high in iron, zinc, magnesium, vitamin B2 and Omega-3 Fatty acids.
Furthermore, it contains all nine of the essential amino acids the body does not produce on its own 
- Spirulina: Known otherwise as a cyanobacterium (a prokaryote, incorrectly referred to as a "blue-green alga"), contains 10% more protein than Chlorella as well as more thiamine and copper. 
The oils from some algae have high levels of unsaturated fatty acids. For example, Parietochloris incisa is very high in arachidonic acid, where it reaches up to 47% of the triglyceride pool.  Some varieties of algae favored by vegetarianism and veganism contain the long-chain, essential omega-3 fatty acids, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). Fish oil contains the omega-3 fatty acids, but the original source is algae (microalgae in particular), which are eaten by marine life such as copepods and are passed up the food chain.  Algae have emerged in recent years as a popular source of omega-3 fatty acids for vegetarians who cannot get long-chain EPA and DHA from other vegetarian sources such as flaxseed oil, which only contains the short-chain alpha-linolenic acid (ALA).
Pollution control Edit
- Sewage can be treated with algae,  reducing the use of large amounts of toxic chemicals that would otherwise be needed.
- Algae can be used to capture fertilizers in runoff from farms. When subsequently harvested, the enriched algae can be used as fertilizer.
- Aquaria and ponds can be filtered using algae, which absorb nutrients from the water in a device called an algae scrubber, also known as an algae turf scrubber. 
Agricultural Research Service scientists found that 60–90% of nitrogen runoff and 70–100% of phosphorus runoff can be captured from manure effluents using a horizontal algae scrubber, also called an algal turf scrubber (ATS). Scientists developed the ATS, which consists of shallow, 100-foot raceways of nylon netting where algae colonies can form, and studied its efficacy for three years. They found that algae can readily be used to reduce the nutrient runoff from agricultural fields and increase the quality of water flowing into rivers, streams, and oceans. Researchers collected and dried the nutrient-rich algae from the ATS and studied its potential as an organic fertilizer. They found that cucumber and corn seedlings grew just as well using ATS organic fertilizer as they did with commercial fertilizers.  Algae scrubbers, using bubbling upflow or vertical waterfall versions, are now also being used to filter aquaria and ponds.
Various polymers can be created from algae, which can be especially useful in the creation of bioplastics. These include hybrid plastics, cellulose-based plastics, poly-lactic acid, and bio-polyethylene.  Several companies have begun to produce algae polymers commercially, including for use in flip-flops  and in surf boards. 
The alga Stichococcus bacillaris has been seen to colonize silicone resins used at archaeological sites biodegrading the synthetic substance. 
The natural pigments (carotenoids and chlorophylls) produced by algae can be used as alternatives to chemical dyes and coloring agents.  The presence of some individual algal pigments, together with specific pigment concentration ratios, are taxon-specific: analysis of their concentrations with various analytical methods, particularly high-performance liquid chromatography, can therefore offer deep insight into the taxonomic composition and relative abundance of natural algae populations in sea water samples.  
Stabilizing substances Edit
Carrageenan, from the red alga Chondrus crispus, is used as a stabilizer in milk products.
Experts say algae is the food of the future. Here's why.
Name the diet, and I've tried it. I'm currently a pescatarian with fish as my main protein source. But I've been a carnivore, vegetarian and vegan, too.
Oh, and I dabble in "menu of the future" items such as algae and bugs.
In the last month, I've had algae smoothies, algae protein bars and algae chips. It's not because I'm a particularly adventurous eater or that I love the taste. I actually loathe the mossy flavor of algae.
I eat it because I'm a worry wart when it comes to our environment. We've gotten ourselves into some trouble. Our dining habits are a big part of the problem.
The average American male consumes 100 grams of protein daily -- almost double the necessary amount. This overconsumption isn't sustainable. The United Nations projects food production will need to increase as much as 70% by 2050 to feed an extra 2.5 billion people.
To survive, we need to reinvent the way we farm and eat. Experts say algae could be a possible solution. Unlike most crops, it doesn't require fresh water to flourish. That's a big deal. About 70% of the planet's available fresh water goes toward crops and raising livestock.
Meat uses up a lot of our finite resources, like water and land, not just for the animals but to grow their food, too. But the green slimy stuff that lives in oceans, ponds and aquariums can grow fast, is packed with nutrition and needs next to nothing to grow. It can even grow in a desert.
My visit at Green Stream Farms in Columbus, New Mexico
Several weeks ago, I visited algae farm Green Stream Farms in the sleepy town of Columbus, New Mexico, a stone's throw away from the Mexican border. With a location that feels like you're in the middle of nowhere and a population of 1,600, you'd never expect this is where the food of the future comes from.
But that's where wellness company iWi is growing a strain of algae on a massive scale. The farm has green seas as far as the eye could see. The entire farm is 900 acres -- 98 of which are currently being cultivated -- and operates all year round.
At the farm, I got my hands dirty. I wadded thigh-high in a sea of green algae and reached my hand into a vat of the harvested "green gold," coating it in cold, verdant goop. Feeling bold, I licked the dripping algae off my finger.
It was a far cry from the gross-tasting algae I've had in the past. That's because not all strains of algae smell or taste like pond scum. Some algae I've tried before even turned my tongue black-green. But the farm's fresh algae simply tasted salty and gave me hope people would willingly eat this.
Up close and personal with the algae
"There are hundreds of thousands of strains of algae in the world and there is a subgroup of those that are stinky and slimy and gross, but there are lots that are not," said Rebecca White, iWi's VP of Operations.
IWi is betting their strain, nannochloropsis, will be next big food trend. The company already sells algae as omega-3 and EPA supplements at the The Vitamin Shoppe and on Amazon. It's now developing algae-based snacks and protein powders.
"The protein we're producing is not going to be green," said CEO Miguel Calatayud, adding its protein powders will be virtually imperceptible when added to other foods. It is "not going to change the flavor."
"[It will be] in every single food that you take on an everyday basis," he added. "Algae is going to be part of a regular food chain for us. It's going to be great thing for all of us and for our planet."
Calatayud said if the world's population grows from 7.5 billion to 10 billion as expected, we'll need to think more seriously about protein alternatives like algae.
"There will not be enough animal protein or other vegetable protein," he said. "There won't be enough arable land, and what's even more important, there won't be enough fresh water."
Algae for as far as the eye can see
IWi's strain of algae takes what would otherwise be wasted -- saltwater, desert land and CO2 -- and turns it into something special. Made up of 40% protein, it can produce about seven times the amount of protein as soybeans on the same amount of land. The plant also releases oxygen into the air. (About 50% of the world's oxygen comes from algae).
"There are tons of desert areas all over the world and most of them have brackish water underneath," he said. "What we are building it's 100% sustainable and 100% scalable."
When it comes to actually growing algae, the approach falls into two classes: an open method in an environment like a pond exposed to the elements, or a closed system in a photobioreactor with a more controlled environment. IWi uses an open method by harnessing the power of the sun to feed its algae.
Algae at the farm is grown in long ponds called "raceways," and an engine constantly churns water to make sure the algae is exposed to the sunlight. CO2 and a tiny bit of fertilizer is then pumped into the water to help the algae bloom.
The farm's algae tasted salty (and not gross)
Algae isn't the only protein alternative scientists are tinkering with. Lab-grown meat companies such as Memphis Meats, Beyond Meats and Impossible Foods are working to popularize cultured meats and plant-based meat substitutes. Their products are currently on supermarket shelves and have a sizable following with vegetarians and vegans.
Other meat alternatives include bugs -- especially crickets, largely considered the tastiest insects. I've popped them into my mouth like potato chips. The hardest part is wrapping your brain around eating something you'd usually spray with Raid or squash with a book.
But they don't taste that bad. I've even had some bug-based dishes that were truly delicious. When crickets are ground into flour for protein powder, it's unrecognizable. Form factor matters.
More than 2,000 edible bug species are eaten by 2 billion people worldwide, and for good reason.
"Insects are rich in protein and essential micronutrients, such as iron and zinc," said Dr Matthias Halwart of the United Nations' Food and Agriculture Organization. "They don't need as much space as livestock, emit less greenhouse gases, and have an excellent feed conversion rate."
For example, a pound of feed yields 12 times more edible cricket protein than beef protein, he said.
Perhaps it's only a matter of time before Western countries stop turning up our noses at plated insects and start chowing down.
And algae for dinner may be a long shot for now, but the powerful potential of this tiny super crop can't be ignored.
Harmful and Useful Activities of Algae | Botany
The algae of different groups like Volvocales, Chlorococcales, Cyanophyceae and several others occur in such a great abundance which makes the water colour either green or blue green and causes the block­age of gills of fishes. As a result during night time (when photosynthesis stops) the respiration of fishes is hampered causing death.
ii. As Parasite on Higher Plants:
Out of many parasitic algae, Cephaleuros is the impor­tant genus. Different species of Cephaleuros grow on the leaves of different angiosperms like Rhododendron, Magnolia, Camellia sinensis (tea), Coffea arabica (coffee) and Piper nigrun (Pepper). Cephaleuros virescens causes Red rust of tea plants, causing economic losses mainly during slow growth.
2. Reducing the O2 Level in Water:
Algae like Microcystis, Anabaena, Aphanisomenon form water blooms and can grow well in O2-deficient water. The continuous respiration by sub­merged plants and animals during night time (when the photosynthesis does not take place) causes the depletion of O2 to almost zero level. At that condition mortality of both animals and other submerged plants takes place due to suffo­cation.
3. Toxicity to Live Stocks (Domestic Ani­mals like Cow, Pig, Horse etc.):
With the increase in algal population, the water becomes difficult to drink by the live stocks. Toxic substances released by some algae make the water poi­sonous and cause the death of livestock’s after drinking that water.
4. Toxicity to Human Being:
Toxins secre­ted by Gymnodinium affect the muscular and nervous systems of some fishes. Gonyaulax catenella secretes an endotoxin, tetraodontoxin (C16H31O16), which accumulates in the body of shell fish. Consumption of such shell fish by human being causes paralysis or even death within a day.
5. Fouling of Ship:
Some algae become attached and grow on the outer surface of ship called fouling, which retards the speed. To over­come such problem the ships are dried at inter­vals and painted with copper paints.
6. Contamination in Drinking Water:
Algae of different groups mainly blue green, green and some others contaminate the water of reservoirs. They develop a foul odour in water and make it unhygienic for human being. Some mucilagi­nous substances are secreted by algae on which many pathogenic bacteria can grow nicely and cause several human and plant diseases.
Different diseases may appear by drinking that water:
i. Chlorella and Lyngbya cause different skin diseases,
ii. Gymnodinium brevis cause respiratory disease, and
iii. Microcystis, Anabaena cause gastric troubles.
7. Blocking of Photosynthesis:
The epi­phytic algae growing on the leaf surface of other plants hamper photosynthesis, thereby the growth of the mother plant becomes reduced.
8. Destruction of Exposed Fibres:
Some blue green algae grow well on the wet exposed fibres, marks by black spots. The algal growth usually follows bacterial growth and the fibres get damaged severely.
Useful Activities of Algae:
Algae are used by man from ancient times, but due to population boom in the last decades the rate of consumption of edible algae has been increased and it will definitely increase much more in near future. The algal species is becoming a popular food to the man­kind because of its high nutritive value and more yield per unit area than the conventional crops.
In Japan, the food production by marine algae is about eight times more than that of land plants.
Some algae commonly used as food are Chlorella, Chondrus, Codium, Porphyra, Rhodymenia, Ulva etc.
It has become popularly known to human beings after its use in the space research and nuclear submarines for the genera­tion of oxygen.
It is also important for its nutritive value and can be compared with soyabeans. It grows very fast in controlled condition and yields about 13 metric tonnes/year/acre. It contains, carbohydrate 30%, protein 30%, lipid 15% etc. But the diges­tion of its cell wall is a problem to the human being and researches are going on to solve it. According to Witsch (1959) the vitamin B con­tent of young culture is equivalent to the lemon juice.
It is commonly known as Irish moss. The alga is cooked with milk and with the addition of vanilla, it makes a highly popular dish, the blancmanges.
The gelatinous carbohydrate obtained from this algae is used in pudding. It is used as stabi­lizer and cleaning agent in beer industry.
These are used as salad in Japan.
It is a seaweed, belongs to Rhodophyceae. It contains carbohydrate 40- 45%, protein 30-35% and vitamin B and C. The common name of food item is laver or nori in Japan, tsats’ai in China, sloke in Britain. It is very popular in different countries including Japan.
L. saccharina is rich in carbohydrate (57%) and the commonly used food is called ‘kombu’.
R. palmata is used to pre­pare a salty confection, commonly known as ‘dulse’.
In Japan, it is used in the preparation of common food, known as ‘aonori’.
It is a blue green alga, rich in protein (60%), vitamin and unsaturated fatty acids. In India it is available as tablet prepared by CFTRI (Central Food Technological Research Institute), Mysore.
It is rich in protein and threonine and is equivalent to the skimmed milk.
N. commune is boiled and used as soup in China.
xi. Spirogyra and Oedogonium:
In South India, Green Laver, a kind of food is prepared from Spirogyra and Oedogonium.
Many algae become popular as fodder due to their vitamin and micronutrient, in addition to their protein and carbohydrate content. The algae commonly used as fodder in different countries are Fucus, Laminaria, Sargassum, Alaria, Rhodymenia, Ascophyllum, Macrocystis etc.
The fat content of milk becomes increased with the addition of seaweed. The seaweeds like Rhodymenia palmata and Ascophyllum esculenta are used to feed the cattle in Scotland, Ireland etc. Macrocystis, the Pacific-coast kelp is used directly or indirectly in the form of powder to feed cattle, hogs and poultry birds in USA because of high mineral and vitamin content.
The algae also become popular as fodder in other countries like France, Norway, Germany, Denmark etc. Macrocystis sp. is rich in vitamins A and E — used as fodder in France. Dried Pelvetia, a seaweed used as cow feed increase the milk yielding capacity of catties.
The iodine and carotene content in egg-yolk increases by feeding the processed sea weeds used as food. The egg lying capacity of the poultry birds also increases by feeding the processed sea weeds like Fucus, Laminaria etc. Sargassum is used as fodder in China.
Algae have been used to develop many products of commercial and phar­maceutical importance. These are Agar-agar, Carrageenan, Diatomite, Alginate, Funori, Medicine etc.
Commercially it is obtained from Gelidium nuditifons, G. pusillum, G. robustrum, Gracilaria verrucosa and also from diffe­rent species of Ahnteltia, Chondrus, Gigartina, Acanthopeltis and Pterocladia.
It is composed of two polysaccharides, agarose and agaropectin. The agar-agar is readi­ly soluble in hot water but not in cold water. At 1.5% concentration it forms a clear, solid and elastic gel on cooling the melted agar to 32-39°C and does not melt again below 85°C.
Southeast Asia and Japan are the main cen­tres of agar-agar production.
For the commercial production of agar-agar following procedure is followed:
Collection of plants from sea → bleached in the sun → boiled the material for few hours → the extract is acidified → material is then frozen and thawed → it is then dried. It is available in the market in the form of cakes, flakes or powder.
The agar-agar is used in food, pharma­ceutical, cosmetic industries and scientific labo­ratories.
It is used in processed cheese, jam, jellies, cream and pudding etc. It is also used as gelling and thickening agent in the preservation and canning of meat and fish.
It is used as laxa­tive, pills, different ointments and also used in drug for slow release when requires.
It is used in cosmetics like lotions etc.
d. Scientific Laboratories:
In scientific laboratories it is used for stiffening the culture medium used at 1.5-2.0% concentration.
It is obtained from the cell wall of Cigartina stellata, Chondrus crispus, the Irish moss and Eucheuma.
It is a phycocolloid, almost similar to agar- agar, but the ash content is higher and requires higher concentration to form solid gels. The phycocolloid consists of K-carrageenan and X-carrageenan.
The carrageenan acts as a blood coagulant. It is also used to stabilise emulsions and to cure cough. It is used as a component of deodorants, cosmetics, toothpastes, paints etc.
It is extracted from the cell wall of some brown algae like Ascophyllum, Fucus, Ecklonia, Macrocystis, Laminaria, Durvillea and Lessonia. The content of alginic acid varies in different genera and ranges from 10-40%. The salts of alginic acid found in the cell wall are the alginates.
It is non-toxic, insoluble in water, viscous, but becomes hard when dry.
In food industries, it is used in the preparation of sauce, soup, cream etc. in textile industry as printing pastes and cosmetics.
It is used in polish, emul­sion paints etc.
It is used in confec­tionary, powders, paints, ice-cream etc.
It is used in the produc­tion of artificial fibres, plastics, rubbers etc.
After the death of diatom cells the outer covering i.e., the silicified wall becomes accumulated at the bottom of water. The accumulation may be thicker during favourable condition. These deposits are called diatomaceous earth or diatomite.
It is very sui­table for use in different industries:
It is used as filter in different industries like sugar (to filter microorganism), oil and chemical industry. Diatomite is also used as filter for battery boxes.
It is used as insulator in boilers and blast furnaces for its heat resistant ability.
It is used as absorbent of liquid nitroglycerine.
Diatomite is used as abrasive (i.e., capable of rubbing or grinding down) substance for manufacture of metal paints, polish, varnish and toothpaste etc. It is also used with bake-lite for fuse and switch boxes.
It is a type of glue, obtained from Gloiopeltis furcata, used as sizing agent in paper and textile industry. In cosmetic industry it is used for curling of hairs and preparation of dyeing.
Chlorellin, an antibiotic is extracted from Chlorella. It is used to control microorganisms like Gram -ve bacteria.
In addition to above, other algae such as Cladophora, Laminaria, Lyngbya and Halidrys are able to synthesize antibiotics.
Both Gram +ve and Gram -ve bacteria can be controlled by the extract of Ascophyllum nodosum. Extracts of Cordium, Corallina and Durvillea etc., are used as vermifuge. In China, an antithelmintic drug ‘Tse-ko-Tsoi’, is prepared from Digenia simplex, a red alga.
Different sea weeds are used as good sources of vitamins:
a. Riboflavin from Porphyra tenera, Gelidium amansii,
b. Thiamine from Rhodomela subfusca,
c. Vitamin C from Porphyra lacinata and
d. Vitamin A from Nitzschia, a diatom.
Various brown algae like Ecklonia, Eisenia, Fucus and Laminaria are the richest source of iodine, used to control goiter. About 100 tonnes of iodine are produced per year in Japan from brown sea weeds.
The Gelidium is used to control stomach disorders.
The cultivation of Nitella in the pond greatly reduces the population of Mosquito, indi­rectly controls malaria.
Members of Cyano- phyceae like Nostoc, Anabaena etc. can fix atmospheric nitrogen and form nitrogenous compounds. These compounds are further absorbed by the plant for their metabolic activity and increase yield.
Minerals like Copper, Cobalt, Chromium, Boron, Iron, Zinc, Vanadium and Manganese are present in high amount in sea weeds. Hence the seaweeds are used as stock feed as well as natural fertiliser.
The Polysiphonia and Rhodomela, the mem­bers of Rhodophyceae are richest source of bromine.
Various brown algae like Ecklonia, Eisenia, Fucus and Laminaria are the richest source of iodine.
Soda and Potash are present at high percen­tage in brown algae, thus the ash of those algae are used in the manufacture of alum, glass wares and soap.
6. Disposal of Sewage:
Water-borne wastes of industry and domestic house are called ‘sewage’. It is rich in sulphur, nitrogen, phospho­rus and potassium. The anaerobic breakdown of sewage, gives out bad odour. So the aerobic breakdown is preferred, which does not give out bad odour and the products can also serve as fertiliser.
Bacteria are carried out in a container and the required oxygen is collected from algae. Unicellular algae like Chlamydomonas, Chlorella, Scenedesmus, Euglena etc. are used in this pro­cess. In turn, ammonia and nitrogen compounds become available to the algae as nutrient.
7. Use in Biological Experiments:
Algae are used as experimental material for different research works. Chlorella has been used to study the path of carbon in photosynthesis and Acetabularia in genetical researches. Halicystis is used to study membrane permeability.
8. Use in the Production of H2 Fuel:
Production of H2 is an important area of biotechnology for the production of non- conventional energy. Different algae like Chlamydomonas, Dunaliella, Porphyridium, Oscillatoria etc. are used in this process. Normally photosynthesis takes place in the above plants and the photosynthetic principal is utilized to gain the goal.
In the first part of photosynthesis, photolysis of water takes place by which water splits into, hydrogen ion (H + ), O2 and electrons. The hydrogenase enzyme of the above algae generates hydrogen gas (H2) from hydrogen ion (H + ). Some Cyanophycean members such as Anabaena etc. are used in this process, but here nitrogenase is utilised as the main hydrogen producing enzyme.
Seaweeds are used extensively as food in coastal cuisines around the world. Seaweed has been a part of diets in China, Japan and Korea since prehistoric times.  Seaweed is also consumed in many traditional European societies, in Iceland and western Norway, the Atlantic coast of France, northern and western Ireland, Wales and some coastal parts of South West England,  as well as New Brunswick, Nova Scotia, and Newfoundland and Labrador. The Māori people of New Zealand traditionally used a few species of red and green seaweed,  and Indigenous Australians ate several species. 
Seaweed contains high levels of iodine relative to other foods.  In the Philippines, Tiwi, Albay residents created 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. 
One study in 2014 pointed to certain species of seaweed as being a possible vegan source of biologically-active Vitamin B12. The study noted that B-12 was found in both raw and roasted seaweed, the latter containing about half as much—but still a sufficient amount. A mere 4 grams of dried purple laver is considered sufficient to meet the RDA for B-12. 
Polysaccharides in seaweed may be metabolized in humans through the action of bacterial gut enzymes. Such enzymes are frequently produced in Japanese population due to their consumption of seaweeds. 
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.
As a nutraceutical product, some edible seaweeds are associated with anti-inflammatory, anti-allergic, antimutagenic, antitumor, antidiabetic, antioxidant, antihyperthensive and neuroprotective properties. Edible red macroalgae such as Palmaria palmata, (Dulse), Porphyra tenera (Nori) and Eisenia bicyclis have been measured as a relevant source of "alternative protein, minerals, and, eventually, fiber." 
Japanese cuisine has seven types of seaweed identified by name, and thus the term for seaweed in Japanese is used primarily in scientific applications, and not in reference to food.
Sea grapes (Caulerpa lentillifera) are cultivated in ponds in the Philippines 
Edible algae—coming to a rooftop near you?
A woman prepares a spirulina shake in Bangkok on June 24, 2013. Proponents of the edible algae known say it could help provide a sustainable source of protein as an alternative to meat.
On a hotel rooftop in Bangkok, dozens of barrels of green liquid bubble under the sun—the latest innovation in urban farming.
Proponents of the edible algae known as spirulina say it could help provide a sustainable source of protein as an alternative to meat.
Three times a week, Patsakorn Thaveeuchukorn harvests the green algae in the barrels.
"The algae is growing so fast, normally the doubling time is around 24 hours," said Patsakorn, whose employer EnerGaia uses Bangkok's rooftops to grow spirulina.
With its high levels of protein and nutrients, "it is beneficial to food security," he told AFP.
"If you compare it to meat it will take six months to grow a kilogram of beef, but this we can grow in a week," said Patsakorn.
Spirulina has been described by health food experts as a super-food, and it is becoming more popular worldwide.
Rosa Rolle from the UN's food and agriculture organisation (FAO) says it has been an important food source for centuries.
"It grows naturally in Lake Texcoco in Mexico. It was eaten by the Incas," she told AFP. "It's in many countries that border Lake Chad in West Africa and is a protein source for a lot of people."
However she warns that it can lead to health problems for people suffering from gout, as it produces a lot of uric acid, and says people need to be educated about spirulina's positive and negative effects before they consume it.A worker checks a spirulina farm on the top of a hotel in Bangkok on June 24, 2013. The empty space on top of Bangkok's many skyscrapers provide suitable growing conditions for spirulina as the constant high temperatures and sunlight are ideal breeding conditions.
"You need some nutritional information, but for people without medical conditions it would be fine," she said.
The empty space on top of Bangkok's many skyscrapers provide suitable growing conditions for spirulina as the constant high temperatures and sunlight are ideal breeding conditions.
The algae also helps combat carbon dioxide levels through photosynthesis, its champions say, and growing it in cities means it can reach consumers the same day it is harvested.
Once the spirulina algae has been collected, it is hand rinsed and spun dry in a modified washing machine.
It then has to be hand pressed into jars, as there is no machine yet available that can work with the thick, jelly like substance it produces.
"There has been a lot of trial and error," Derek Blitz, technology director at EnerGaia, told AFP.
"It is great for vegetarians and vegans. It's also packed with anti-oxidants. It is really good for cleansing your body."
In their laboratory, lines of different sized test tubes all connected to one another act as the breeding ground for the algae. On the rooftop, barrels of different shapes are in testing, to see which will produce the highest yield.
The company says it is the only producer of fresh spirulina in the world other companies only sell dried and processed varieties.Fresh spirulina is pictured at a spirulina farm on the top of a hotel in Bangkok on June 24, 2013. Spirulina has been described by health food experts as a super-food, and it is becoming more popular worldwide.
Jars of the algae have a shelf life of around three weeks from harvest, though Blitz plans to increase that so it can be exported abroad.
"The advantages of having it fresh are that it has virtually no taste, so you can mix it with anything," he told AFP.
"Eating dried spirulina is like eating a cooked vegetable as opposed to a raw one, so you are getting a little bit more nutrition out of it (when fresh). The other reason to eat fresh produce is because there's a lot less energy involved in producing it."
And chefs across Bangkok are starting to experiment with the algae. Bill Marinelli, the owner of the Oyster Bar, is a convert.
"It is really good for you," he told AFP, in between mouthfuls of green pasta made with the algae. "We add it to dishes to increase the nutritional value."A spirulina laboratory is pictured in Bangkok on June 24, 2013. The algae helps combat carbon dioxide levels through photosynthesis, its champions say, and growing it in cities means it can reach consumers the same day it is harvested.
The colour of the algae is so strong that anything it is mixed with instantly turns green. But despite that, and the fact it has no flavour, Bill is still keen to use it in his dishes.
"I'm looking at it as an alternative to animal protein. We can cut back on the amount of protein we serve as fish or meat, and incorporate spirulina for the additional protein source," he said.
Spirulina has been used as a food supplement for decades, and is popular among body builders. The question now is whether consumers will see it as a possible alternative to meat and fish.
Pond Algae Identification – Which Algae Is That?
Within the 8 main groups (phyla) mentioned above are dozens of smaller groups encompassing more than one million species of algae – here we will simply discuss the groups that are most common in garden ponds and lakes, with pictures to help with identification:
1) Green Water Algae
Green water algae can turn ponds a “pea-soup” color, but they are also a natural and healthy food source to many different animals.
Green algae, belonging to the family chlorophyta, is the most diverse group of algae encompassing over 7,000 species. These algae are present in most healthy pond and lake ecosystems, as they are at the base of the food web. Their chloroplasts contain both chlorophyll A and B, accounting for their typical bright green coloration, though they may also be various hues of yellow. In addition to providing food for a variety of creatures from fish to insects to waterfowl, green algae are also primary producers, generating oxygen and energy/nutrients that are then utilized by organisms that are unable to produce their own. Conversely, as previously mentioned, too much green algae (often as a result of nutrient-rich water) can result in eutrophication, ultimately resulting in depleted oxygen levels and the death of your pond’s inhabitants, especially in warmer summer months months. It’s important to control the spread of green water algae before it gets to this point, with the most effective treatments being UV clarification, water dyes, and good filtration and maintenance.
2) Cyanobacteria (Blue-Green Algae)
As indicated by its name, cyanobacteria, while commonly referred to as blue-green algae, is not a true algae but rather a type of bacteria that looks deceivingly similar to algae. They prefer shallow, warm, still water that is rich in nutrients…in other words, they thrive in unhealthy, low quality aquatic ecosystems! They typically form dense, scum-like floating mats on the water’s surface and can range in color from the characteristic blue-green to green, yellow, purple, or brown. If your pond or lake has a strong, unpleasant odor and algae-like mats that are viscous and slimy, you likely have a cyanobacteria bloom. Another way to determine whether you have an overabundance of cyanobacteria (the presence of some cyanobacteria is normal and not harmful) is to conduct a water quality test – poor water quality with low oxygen and high nitrogen levels are a decent indicator of cyanobacteria presence, particularly if accompanied by a foul smell and dead or dying/unhealthy fish. When testing your water, be sure to wear protective clothing such as rubber gloves and waders – cyanobacteria contain various toxins that are harmful if touched or ingested. Different types of cyanobacteria present different health hazards, so be sure to minimize your exposure and thoroughly clean yourself and your clothing if you come into contact with any.
Left uncontrolled, blue-green algae forms a thick toxic sludge on ponds and lakes. Photo credit: http://instituteddec.org
When their numbers aren’t out of control, cyanobacteria do have some ecological benefits: some species of fungi and lichen have formed a symbiotic relationship with cyanobacteria, allowing it to live in their roots where the bacteria help to fix nitrogen into a form that is usable by the plant or fungus. Cyanobacteria is also present in many soils, where they also aid in nitrogen fixation that is essential for proper ecosystem functioning. In addition, the chloroplasts of modern plants (the part a plant’s cells that conducts photosynthesis and produces food for the plant) actually developed from ancestral cyanobacteria! Plant chloroplasts evolved from cyanobacteria hundreds of millions of years ago via endosymbiosis, a process that entails one organism living within another in such a way that both organisms benefit while adapting and evolving together over time. With this in mind, plant life as we know it would not exist were it not for cyanobacteria – so it’s certainly not all bad!
3) String Algae (Filamentous)
String algae, or filamentous algae, forms hair-like strands under the water, often sticking to rocks, ornaments and pond liners.
String algae, also called filamentous algae, are single-celled organisms that link together to form – you guessed it! – long strings that in turn intertwine and form mats. Still water, plenty of sunlight, and the proper concoction of nutrients give rise to this algae, which starts off forming on rocks and substrate at the bottom of the water and then rises to the water’s surface as it links together, grows, and oxygen bubbles collect within the hair-like fibers, creating buoyancy. Belonging to the chlorophyta family and therefore a variety of green algae, string algae are most commonly green but can also be shades of yellow or brown. Some familiar filamentous algae species are blanketweed or watersilk (spirogyra), horsehair algae (pithophora), and cotton algae (cladophora).
Like most types of green algae, string algae are an essential food source for young fish, waterfowl, and aquatic insects, and also generate oxygen. Their propensity to colonize into mats can create issues such as clogging water filters and pumps, blocking sunlight, consuming dissolved oxygen, generating ammonia (and then converting that into potentially harmful nitrates and nitrites), and ultimately depleting water quality. You can control filamentous algae by utilizing naturally occurring microbes, vacuuming/raking out any mats that are present, and regularly monitoring your water quality to prevent algae overgrowth.
4) Euglena Algae
Euglena blooms are quite distinctive, causing a deep green or crimson water color. Photo credit: https://aquaplant.tamu.edu
Euglena, belonging to the family euglenaceae and phyla euglenophyta, contains over 1,000 species and is incredibly diverse and resilient, able to exist in any water body around the world as well as most moist soil types. Typically green or red, this type of algae is often quite alarming – and for good reason. When euglena is present, you typically won’t know it until a bloom occurs, often bright crimson in color. These blooms are incredibly toxic, and will result in fish and vegetation die offs unless brought under control. Unfortunately, most euglena species do not respond to manual or biological controls, so you’ll have to either entirely drain your water body and replace it with fresh water, or utilize chemical products to kill off the bloom. The most effective chemical controls for euglena often contain copper or sodium carbonate. The downside of employing chemical controls, as discussed in previous articles, is the potential to harm the flora and fauna in your lake or pond. There are no known benefits of euglena, other than its presence indicating poor water quality and thus warning that something needs to change.
5) Chara Algae
Chara Algae – Photo by Mnolf available under a Creative Commons’s Attribution-Share Alike 3.0 Unported license.
Chara, or muskgrass, also belongs to the green algae family. This type of alga is often mistaken for a plant because they possess structures that look quite similar to leaves and stems. However, these are not true leaves or stems, nor does it possess reproductive structures (such as ovum or flowers). It’s not known to be overly detrimental to pond health, other than producing a pungent odor similar to that of garlic (giving rise to the name muskgrass!), and, like most algae, being prone to overgrowth. In fact, it’s known as the “filter algae,” as it naturally helps to filter out pollutants and add dissolved oxygen to the water. Muskgrass is commonly consumed by waterfowl and provides habitat for aquatic insects, which are in turn eaten by fish. Their root-like structures, called rhizoids, also help to stabilize the sediment at the water’s bottom, thus preventing murky water.
Quest for edible malarial vaccine leads to other potential medical uses for algae
The scientists used a protein produced by the bacterium responsible for cholera, Vibrio cholera, that binds to intestinal epithelial cells. Credit: Wikimedia
(Phys.org) —Can scientists rid malaria from the Third World by simply feeding algae genetically engineered with a vaccine? That's the question biologists at UC San Diego sought to answer after they demonstrated last May that algae can be engineered to produce a vaccine that blocks malaria transmission. In a follow up study, published online today in the scientific journal Applied and Environmental Microbiology, they got their answer: Not yet, although the same method may work as a vaccine against a wide variety of viral and bacterial infections.
In their most recent study, which the authors made freely available on the Applied and Environmental Microbiology website, the researchers fused a protein that elicits an antibody response in mice against the organism that causes malaria, Plasmodium falciparum, which afflicts 225 million people worldwide, with a protein produced by the bacterium responsible for cholera, Vibrio cholera, that binds to intestinal epithelial cells. They then genetically engineered algae to produce this two-protein combination, or "fusion protein," freeze dried the algae and later fed the resulting green powder to mice. The researchers hypothesized that together these proteins might be an effective oral vaccine candidate when delivered using algae.
The result? The mice developed Immunoglobulin A (IgA) antibodies to both the malarial parasite protein and to a toxin produced by the cholera bacteria. Because IgA antibodies are produced in the gut and mucosal linings, they don't protect against the malarial parasites, which are injected directly into the bloodstream by mosquitoes. But their study suggests that similar fusion proteins might protect against infectious diseases that affect mucosal linings using their edible freeze-dried algae.
"Many bacterial and viral infections are caused by eating tainted food or water," says Stephen Mayfield, a professor of biology at UC San Diego who headed the study. "So what this study shows is that you can get a really good immune response from a recombinant protein in algae that you feed to a mammal. In this case, it happens to be a mouse, but presumably it would also work in a human. That's really encouraging for the potential for algae-based vaccines in the future."The edible algae Chlamydomonas, seen here at UC San Diego, can be grown in ponds anywhere in the world. Credit: SD-CAB
The scientists say bacterial infections caused by Salmonella, E. coli and other food and water-borne pathogens could be prevented in the future with inexpensive vaccines developed from algae that could be eaten rather than injected. "It might even be used to protect against cholera itself," said James Gregory, a postdoctoral researcher in Mayfield's lab and the first author of the paper. In his experiments with mice, he said, Immunoglobulin G (IgG) antibodies—which are found in blood and tissues—were produced against the cholera toxin, "but not the malaria antigen and we don't quite understand why."
Part of the difficulty in creating a vaccine against malaria is that it requires a system that can produce structurally complex proteins that resemble those made by the parasite, thus eliciting antibodies that disrupt malaria transmission. Most vaccines created by engineered bacteria are relatively simple proteins that stimulate the body's immune system to produce antibodies against bacterial invaders.
Three years ago, a UC San Diego team of biologists headed by Mayfield, who is also the director of the San Diego Center for Algae Biotechnology, a research consortium seeking to develop transportation fuels from algae, published a landmark study demonstrating that many complex human therapeutic proteins, such as monoclonal antibodies and growth hormones, could be produced by the common algae Chlamydomonas. That got Gregory wondering if complex malarial transmission blocking vaccine candidates could also be produced by Chlamydomonas. Two billion people live in malaria endemic regions, making the delivery of a malarial vaccine a costly and logistically difficult proposition, especially when that vaccine is expensive to produce. So the UC San Diego biologists set out to determine if this alga, an organism that can produce complex proteins very cheaply, could produce malaria proteins that would inhibit infections from malaria.
"It's too costly to vaccinate two billion people using current technologies," explained Mayfield. "Realistically, the only way a malaria vaccine will ever be used in the developing world is if it can be produced at a fraction of the cost of current vaccines. Algae have this potential because you can grow algae any place on the planet in ponds or even in bathtubs."
Collaborating with Joseph Vinetz, a professor of medicine at UC San Diego and a leading expert in tropical diseases who has been working on developing vaccines against malaria, the researchers showed in their earlier study, published in the open access journal PLoS ONE last May that the proteins produced by the algae, when injected into laboratory mice, made antibodies that blocked malaria transmission from mosquitoes.
The next step was to see if they could immunize mice against malaria by simply feeding the genetically engineered algae. "We think getting oral vaccines in which you don't have to purify the protein is the only way in which you can make medicines dramatically cheaper and make them available to the developing world," says Mayfield. "The Holy Grail is to develop an orally delivered vaccine, and we predict that we may be able to do it in algae, and for about a penny a dose. Our algae-produced malarial vaccine works against malarial parasites in mice, but it needs to be injected into the bloodstream."
Although an edible malarial vaccine is not yet a reality, he adds, "this study shows that you can make a pretty fancy protein using algae, deliver it to the gut and get IgA antibodies that recognize that protein. Now we know we have a system that can deliver a complex protein to the right place and develop an immune response to provide protection."
Mayfield is also co-director of the Center for Food & Fuel for the 21st Century, a new research unit that has brought together researchers from across the campus to develop renewable ways of improving the nation's food, fuel, pharmaceutical and other bio-based industries and is this week hosting a major symposium on the subject at the Institute of the Americas at UC San Diego.