Brown algae, like red algae, almost always live in the seas and oceans, that is, in salt water. All of them are multicellular. Among brown algae, there are the largest representatives of all algae. Mostly brown algae grow at shallow depths (up to 20 m), although there are species that can live at depths up to 100 m. In the seas and oceans, they form peculiar thickets. Most brown algae live in subpolar and temperate latitudes. However, there are those that grow in warm waters.

Brown algae, like green algae, are capable of photosynthesis, that is, their cells contain the green pigment chlorophyll. However, they also have many other pigments that have yellow, brown, orange colors. These pigments "interrupt" the green color of the plant, giving it a brownish tint.

As you know, all algae belong to lower plants. Their body is called the thallus, or thallus, there are no real tissues and organs. However, in a number of brown algae, a dismemberment of the body into similar organs is observed; different tissues can be distinguished.

Some species of brown algae have a complexly dissected thallus, having a length of more than 10 m.

The vast majority of brown algae are attached to underwater objects. They do this with the help of rhizoids or the so-called basal discs.

Brown algae exhibit different types of growth. Some species grow with their apex, in others all the cells of the thallus retain the ability to divide, in others the surface cells divide, and in the fourth there are special zones of cells in the body, the division of which leads to an increase in tissues above and below them.

The cell membranes of brown algae consist of an inner cellulose layer and an outer gelatinous layer, which includes various substances (salts, proteins, carbohydrates, etc.).

Cells have one nucleus, many small disk-shaped chloroplasts. Chloroplasts differ in structure from the chloroplasts of higher plants.

As a reserve nutrient in the cells of brown algae, not starch is deposited, but another polysaccharide and one of the alcohols. Cells contain vacuoles with polyphenolic compounds.

Brown algae have both sexual and asexual reproduction. They can reproduce by fragmenting their thallus, and some species form brood buds. Asexual reproduction is also carried out by spores produced in sporangia. Most often, spores are motile (have flagella), that is, they are zoospores. The spores give rise to the gametophyte, which forms germ cells, the fusion of which gives rise to the sporophyte. Thus, in brown algae, alternation of generations is observed. However, in other species, gametes are formed by the sporophyte, that is, the haploid stage is represented only by eggs and spermatozoa.

It is noted that brown algae emit pheromones that stimulate the release of spermatozoa and their movement to the eggs.

The most famous representative of brown algae is kelp, which a person eats, calling it seaweed. She has rhizoids, with which she attaches herself to underwater objects (stones, rocks, etc.). Laminaria has a semblance of a stem (stem), this part of the plant is not flat, but cylindrical. The length of the stem is up to half a meter, similarities of flat sheet plates (several meters each) depart from it.

Brown algae are used by humans not only for food, they are used in the food and textile industries, some medicines are made from them.

If you notice brown mucus on the walls of the aquarium, it's time to sound the alarm - harmful algae has started in your pond. She leaves her marks on the bottom and on the leaves of aquatic plants. If you do not fight brown algae, it will clog the reservoir very quickly, worsening the habitat for fish.

What is brown algae

Brown algae are microscopic living organisms that can exist both unicellularly and take the form of colonies. They are referred to as diatoms, which means "divided in half."

This is their structure: 2 halves of a single whole - epithecus (upper) and hypothecus (lower). All this is denounced in a single hard shell. Through its porous walls, the metabolism of brown algae occurs.

Like any protozoan, brown algae reproduce by division. When divided, the daughter cell gets a piece of the mother's shell. And these halves of the shell are able to recreate themselves, dressing both the "mother" and the "daughter" in new armor.

Since the shells are impregnated with silica, they are not able to increase in size. Because of this, each subsequent generation of diatoms is smaller than its ancestors. But they also manage to leave brown raids on any surface of the aquarium.

Among these algae there are also individuals that gather in tubular colonies that have the shape of brown bushes. They grow very quickly, sometimes reaching a height of 20 centimeters. But to a greater extent, they look like flat formations that we perceive as plaque.

Brown algae prefer shady corners of water bodies with an abundance of organic matter. This just encourages them to actively develop. Filling the entire aquarium, this algae deprives other inhabitants of the right to a normal existence.

Reasons for the appearance of diatoms

If the reservoir is new, then the appearance of brown blotches on the walls of the aquarium or the surface of the water in a couple of weeks is considered the norm. The reason is still uninhabited habitat - a fairly high content of carbon and organic matter in the water. Apparently, there are still a small number of fish and green vegetation in the reservoir that would absorb all this abundance.

But if the “brown junta” began to take over the space of the old aquarium, then here one should already think about where the regime was violated.

• Perhaps the aquarium is not well lit - "drillers" are very fond of partial shade.
• The increased content of iodine is also the cause of brown algae.
• Brown algae also receive nourishment from the silicates contained in the reservoir. Their source can be substrates containing silicon, or sand at the bottom of the reservoir.

But no matter which of the reasons that affect the appearance of brown algae, it is necessary to start fighting it immediately, as soon as the first signs of a problem are noticed.

Brown algae control

To make the inhabitants of your home pond feel comfortable enough, get rid of brown algae by all available means. Don't let these "amoebae" breed in your aquarium.

• In a young aquarium, it will be enough to do mechanical work, removing all plaque from the surfaces. To do this, you can purchase a special scraper or take a regular blade.
• From the leaves of aquatic plants, you will have to clean off brown raids simply with your hands. Never use foam or sponge material to remove algae. And do the cleaning carefully so as not to damage the plants.
• Do not forget about the accumulated dirt at the bottom of the reservoir - it is better to remove it with the help of a hose designed for this.
• Remove pebbles, shells, pebbles (when changing water) from the aquarium and rinse them well. Do the same with decorative elements (artificial locks, decorative snags, etc.).
• Rinse should also be under running water and filters, as well as compressor hoses.
• Get a “biological weapon” in the aquarium - fish that feed on brown algae: girinocheilus, catfish ancistrus, Siamese algae eater, etc. Mollusks (neritic olive snail, horned snail) are also good cleaners.

But various chemicals to combat brown "evil spirits" should not be used - harm other inhabitants of the reservoir. But some antibiotics (such as penicillin) can be used. And be sure to put the aquarium as close to the light as possible.

Preventive measures

To no longer have to deal with such a scourge as brown algae, follow the basic rules for caring for home water bodies.

• First of all, ensure that there is sufficient lighting in every corner of the aquarium. If daylight hours are too short, use additional lighting fixtures. It is better to use lamps that give red spectral light.
• Always keep the temperature in the reservoir at the optimum level (+ 22-28 0 C) - brown algae like just the opposite, cooler.
• Regularly change the water in the aquarium, monitor its technical indicators (pH, iodine, nitrates, phosphates, silicates). Never use water directly from the tap - only purified water is needed.
• Install filters in the pond that can absorb silicates
• Plant an aquarium with a large number of aquatic plants - they will "take away" part of the nutrition from brown algae, thereby slowing down its growth.
• Aquarists with experience recommend putting zinc and copper products on the bottom of the reservoir. These metals are capable of destroying brown algae.

Every time you do a water change or kelp cleaning, provide the inhabitants of the reservoir with round-the-clock lighting for several days.

How to get rid of brown algae:

• Brown algae are common in the seas and oceans of the whole world, they live mainly in coastal shallow waters, but also far from the coast, for example, in the Sargasso Sea. They are an important component of benthos.
• The brown color of the thallus is due to a mixture of different pigments: chlorophyll, carotenoids, fucoxanthin. A set of pigments enables photosynthetic processes, since chlorophyll does not capture those wavelengths of light that penetrate to depth.
• In lowly organized filamentous brown algae, the thallus consists of one row of cells, while in highly organized cells not only divide in different planes, but partly differentiate, as if forming "petioles", "leaves" and rhizoids, with the help of which the plant is fixed in the substrate.
• Cells of brown algae are mononuclear, chromatophores are granular, numerous. Spare products are contained in them in the form of polysaccharide and oil. Pectin-cellulose walls are easily mucilaginous, growth is apical or intercalary.
• Asexual reproduction (absent only in fucus) is provided by numerous biflagellate zoospores, which are formed in unicellular, less often multicellular zoosporangia.
• Asexual vegetative reproduction is carried out by parts of the thallus.
• Forms of the sexual process: isogamy, heterogamy and oogamy.
• In all brown algae, except for Fucus, a change in the phases of development is expressed. Reduction division occurs in zoosporangia or sporangia, they give rise to a haploid gametophyte, which is bisexual or dioecious. The zygote without a dormant period germinates into a diploid sporophyte. In some species, the sporophyte and gametophyte do not differ externally, while in others (for example, in kelp), the sporophyte is more powerful and more durable. In fucus, gametophyte reduction is observed, since the gametes fuse outside the mother plant, in the water. The zygote, without a dormant period, develops into a diploid sporophyte.

Among brown algae, there are both microscopic and macroalgae. The latter can reach gigantic sizes: for example, algae macrocystis can reach 30-50 m in length. This plant grows very quickly, giving a large amount of extracted biomass, per day the algae thallus grows by 0.5 meters. In the thallus of macrocystis, sieve tubes similar to those found in vascular plants appeared during evolution. A special group of substances is extracted from macrocystis species - alginates - mucous intercellular substances. They are widely used as thickening agents or colloid stabilizers in the food, textile, cosmetic, pharmaceutical, pulp and paper, and welding industries. Macrocystis can produce several crops per year. Now attempts are being made to cultivate it on an industrial scale. In the thickets of macrocystis, hundreds of species of animals find protection, food, breeding grounds. C. Darwin compared its thickets with terrestrial tropical forests: “If forests were destroyed in any country, then I don’t think that approximately the same number of animal species would die as with the destruction of thickets of this algae.”

Fucus is a dichotomously branching brown alga with air bubbles at the ends of the plates. The thalli reach 0.5-1.2 m in length and 1-5 cm in width. These algae densely cover many rocky areas exposed at low tide. When algae are flooded with water, air-filled bubbles carry them to the light. The rate of photosynthesis in frequently exposed seaweeds can be up to seven times faster in air than in water. Therefore, algae occupy the coastal zone. Fucus does not have an alternation of generations, but there is only a change in nuclear phases: the whole algae is diploid, only gametes are haploid. There is no reproduction by spores.

Two species of the genus sargassum, which do not reproduce sexually, form huge, free-floating masses in the Atlantic Ocean, this place is called the Sargasso Sea. Sargassum swim, forming continuous thickets near the surface of the water. These thickets stretch for many kilometers. Plants are kept afloat thanks to air bubbles in the thallus.

Laminaria ("kombu") in China and Japan are regularly used as vegetables; sometimes they are bred, but mainly they are taken from natural populations. Seaweed (kelp) is of the greatest economic importance; it is prescribed for sclerosis, impaired activity of the thyroid gland, as a mild laxative. Previously, it was burned, the ash was washed, the solution was evaporated, in this way soda was obtained. Soda was used to make soap and glass. As early as the beginning of the 19th century, 100,000 tons of dry algae were burned in Scotland per year. Since 1811, thanks to the French industrialist Bernard Courtois, iodine began to be obtained from kelp. In 1916, 300 tons of iodine were extracted from seaweed in Japan. Laminaria is a large brown alga 0.5-6 m long, consists of leaf-like plates, legs (trunk) and structures for attachment to the substrate (rhizoids). The meristem zone is located between the plate and the stem, which is very important for industrial use. When the fishermen cut off the regrown plates of this algae, its deeper parts regenerate. The trunk and rhizoids are perennial, and the plate changes annually. This structure is characteristic of a mature sporophyte. On the plate, unilocular zoosporangia are formed, in which mobile zoospores mature, germinating into gametophytes. They are represented by microscopic, filamentous outgrowths consisting of several cells that carry the genitals. Thus, kelp has a heteromorphic cycle with a mandatory alternation of generations.

Department of Red Algae. general characteristics

• Red algae are common in the seas of tropical and subtropical countries and partly in the temperate climate (the coast of the Black Sea and the coast of Norway). Some species are found in fresh water and on soil.
• The structure of the thallus of red algae is similar to the structure of the thalli of the most highly organized brown algae. The thallus has the form of bushes, composed of multicellular branching filaments, less often lamellar or leaf-shaped, up to 2 m in length.
• Their color is due to pigments such as chlorophyll, phycoerythrin, phycocyanin. They live in deeper waters than brown ones and require additional pigments to capture light. Due to the presence of phycoerythrin and phycocyanin, they got their name - red algae.
• Chromatophores in red algae are disc-shaped, pyrenoids are absent. Spare products are contained in them in the form of oil and purple starch, specific to red algae, which turns red from iodine. Pectin-cellulose cell walls in some species become so mucilaginous that the entire thallus acquires a slimy consistency. Therefore, some species are used to obtain agar-agar, which is widely used in the food industry for the preparation of nutrient media for the cultivation of bacteria and fungi. The cell walls of some red algae can be encrusted with calcium carbonate and magnesium carbonate, giving them the hardness of stone. Such algae are involved in the formation of coral reefs.
• Red algae do not have mobile stages in the development cycle. They are characterized by a very special structure of the organs of sexual reproduction and the form of the sexual process. Most purples are dioecious plants. Mature spermatozoa (one immobile gamete) exit the antheridia into the aquatic environment and are transported by water currents to the karpogon (the female organ of sexual reproduction). The content of the spermatozoa penetrates into the abdomen of the carpogon and merges with the egg there. The zygote without a dormant period divides by mitosis and grows into filiform thalli of different lengths. Thallus is diploid. In the upper part of these threads, spores of sexual reproduction (carpospores) are formed. During asexual reproduction, sporangia are formed on the thallus, which contain one spore - monospore, or four - tetraspores. Before the formation of tetraspores, reduction division occurs. In monospore algae, gametangia and sporangia are formed on the same monoploid plant, only the zygote is diploid. Tetraspores are characterized by an alternation of developmental phases: haploid tetraspores germinate into a haploid gametophyte with gametangia; diploid carpospores germinate into diploid plants with sporangia (diploid sporophyte). Gametophyte and sporophyte are indistinguishable in appearance. In porphyry and porphyridium, asexual reproduction is carried out by monoploid monospores. They go through the entire development cycle in a haploid state; only the zygote is diploid in them (as in many algae).

Porphyry red algae is the food of many people in the North Pacific and has been cultivated for centuries in Japan and China. More than 30,000 people are employed in the production of this species in Japan alone, and the resulting production is estimated at about 20 million dollars annually. Salads, seasonings, soups are prepared from it. Eaten dried or candied. A famous dish is "nori" - rice or fish wrapped in dried seaweed. In Norway, at low tide, sheep are released on the coastal part, rich in red algae, as if on a pasture. This is one of the typical representatives of crimson. The leaf-like purple thallus of species of this genus is attached to the substrate with its base and reaches 0.5 m in length.

Lives in the Black Sea. Half of the agar obtained in Russia is produced from this purple.

Distribution of algae in water and on land. The value of algae in nature and economy.

Most of these algae live in freshwater reservoirs and seas. However, there are ecological groups of terrestrial, soil algae, snow and ice algae. Algae living in water are divided into two large ecological groups: planktonic and benthic. Plankton is a collection of small, mostly microscopic organisms freely floating in the water column. The plant part of the plankton, formed by true algae, and some crimson, is phytoplankton. The importance of phytoplankton for all inhabitants of water bodies is enormous, since plankton produces the bulk of organic substances, due to which the rest of the living world of water exists directly or indirectly (through food chains). Diatoms play an important role in the formation of phytoplankton.

Benthic algae include macroscopic organisms attached to the bottom of water bodies or to objects and living organisms in the water. Most benthic algae live at depths of up to 30–50 m. Only a few species, predominantly purple algae, reach depths of 200 m or more. Benthic algae are an important food for freshwater and marine fish.

Terrestrial algae are also quite numerous, but usually overlooked due to their microscopically small size. However, the greening of the sidewalks, powdery green coatings on the trunks of thick trees indicate accumulations of soil algae. These organisms are found in the soils of most climatic zones. Many of them contribute to the accumulation of organic matter in soils.

Ice and snow algae are microscopically small and are found only when a large number of individuals accumulate. The phenomenon of the so-called "red snow" has long been most famous. The main organism that causes the reddening of snow is one of the types of unicellular algae - snow chlamydomonas. In addition to free-living algae, algae play an important role in nature - symbionts, which are the photosynthetic part of lichens.

Due to the wide distribution of algae, they are of great importance in the life of individual biocenoses and in the cycle of substances in nature. The geochemical role of algae is associated primarily with the circulation of calcium and silicon. Making up the bulk of the plant, aquatic environment and participating in photosynthesis, they serve as one of the main sources of organic matter in water bodies. In the World Ocean, algae annually create about 550 billion tons (about ¼) of all organic matter on the planet. Their yield here is estimated at 1.3 - 2.0 tons of dry matter per 1 g of water surface per year. Their role is enormous in the nutrition of hydrobionts, especially fish, as well as in the enrichment of the Earth's hydrosphere and atmosphere with oxygen.

Some algae, together with heterotrophic organisms, carry out the processes of natural self-purification of waste and polluted waters. They are especially useful in open "oxidation ponds" used in tropical and subtropical countries. Open ponds with a depth of 1 to 1.5 m are filled with untreated wastewater. In the process of photosynthesis, algae release oxygen and provide vital activity for other aerobic microorganisms. Many of the algae are indicators of pollution and salinization of habitats. Soil algae are actively involved in soil formation.

The economic significance of algae lies in their direct use as food products or as raw materials for obtaining various substances valuable to humans. For this purpose, especially those species whose ash is rich in sodium and potassium salts are used. Some brown algae are used as fertilizers and for pet food. Algae is not particularly nutritious, because. a person does not have enzymes that allow the breakdown and digestion of cell wall substances, but they are rich in vitamins, iodine and bromine salts, and trace elements.

Seaweed is a raw material for some industries. The most important products derived from them are agar-agar, algin and carrageenan. agar - a polysaccharide that is obtained from red algae. It forms gels and is widely used in food, paper, pharmaceutical, textile and other industries. Agar is indispensable in microbiological practice in the cultivation of microorganisms. Capsules for vitamins and medicines are made from it, they are used to obtain impressions of teeth, in cosmetics. In addition, it is introduced into the composition of bakery products so that they do not stale, in the formulation of quick-setting jellies and confectionery products, and is also used as a temporary casing for meat and fish in tropical countries. Agar is obtained from anfeltia, mined in the White and Far Eastern seas. Algin and alginates , extracted from brown algae (kelp, macrocystis), have excellent adhesive properties, are non-toxic, form gels. They are added to food products, tablets in the manufacture of medicines, used in leather dressing, in the production of paper and fabrics. Soluble threads used in surgery are also made from alginates. Carrageenan similar to agar. It is preferred over agar when stabilizing emulsions, cosmetics and dairy products. The possibilities for the practical use of algae are far from being exhausted.

Under certain conditions, algae "bloom", i.e. accumulate in large quantities in water. "Blossoming" is observed in sufficiently warm weather, when there is observed in the water eutrophication , i.e. a lot of nutrients (industrial effluents, fertilizers from the fields). As a result, the explosive reproduction of primary producers - algae - begins, and they begin to die off before they have time to be eaten. In turn, this causes an intensive reproduction of aerobic bacteria, and the water is completely deprived of oxygen. Fish and other animals and plants are dying. Toxins formed during water blooms increase the death of animals, they can accumulate in the body of mollusks and crustaceans that feed on algae, and then, when they enter the human body, cause poisoning and paralysis.

18. Department 9. Brown algae - Phaeophyta (Phaeophycophyta, Phaeophyceae) (N. A. Moshkova)

Brown algae are predominantly marine multicellular plants, very large, complexly dissected, attached to the substrate. Currently, about 1500 species of brown algae belonging to 240 genera are known. In the fresh, mostly cold running waters of temperate latitudes, 5 species of brown algae have so far been found. Due to the small size of their thalli and rare occurrence, they remain a poorly studied group of plants both biologically and ecologically.

A common external feature of brown algae individuals is the yellowish-brown color of their thalli, due to the presence of a large amount of yellow and brown pigments. Thalluses can be microscopic (several tens of micrometers) and gigantic (30-50 m; in some species of the genera Laminaria Lamour., Macrocystis Ag., Sargassum Ag.). The shape of the thalli is very diverse: filiform, corky, saccular, lamellar (solid or with ruptures, outgrowths and numerous holes, smooth or with longitudinal folds and ribs), as well as bushy.

The thalli of brown algae of the order Ectocarpales are most simply organized. In primitive organisms (Bodanella Zimmerm.), the thallus is represented by single-row randomly branching filaments in one plane, tightly adjacent to the substrate. Species of the genus Ectocarpus Lyngb. have bushy thalli formed by single-row ascending, abundantly branching threads, the base of which are creeping rhizoids (Fig. 18.1).

In some representatives of the order Chordariales, the ascending filaments are connected into bundles enclosed in mucus. At the same time, a single-axis type of structure of the thallus is distinguished, in which one thread rises from the base, and other threads branch off from it, running next to it, and a multi-axial type of structure, when a bundle of single-row threads immediately rises from the base. In highly organized brown algae (Laminaria, Fucus Tourn., Sargassum), the thalli are differentiated and resemble flowering plants. They have stem, leaf and root parts, some large representatives have air bubbles that hold the branches in an upright position.

The growth of brown algae is intercalary or apical. In the most primitive forms, intercalary diffuse growth occurs, in more evolutionarily advanced algae, an intercalary growth zone is already outlined. It is usually located in the basal part of multicellular hairs and causes the trichothal growth characteristic of brown algae.

On the surface of single-row thalli of brown algae, multicellular filamentous hairs are formed. At the same time, real and false hairs are distinguished. Real hairs have an intercalary growth zone at the base, where the cells divide frequently and therefore they are smaller, short-cylindrical or disc-shaped. False hairs do not have such a special growth zone and are a continuation of vegetative single-row filaments with strongly elongated cells devoid of chloroplasts.

In the multi-row thalli of brown algae, specialization of cells with the formation of tissues is observed - a parenchymal type of body structure. In the simplest case, a cortex is distinguished from intensely colored cells containing a large number of chloroplasts and special vacuoles - physodes, and a core consisting of colorless, often larger cells of the same shape. In more complexly organized brown algae (Laminariaceae, Fucaceae), the crustal layer reaches a considerable thickness and consists of intensely colored cells of various sizes and shapes (Fig. 18.2). The surface four layers of the cortex are formed by small cells, elongated towards the surface. These upper layers are called meristoderm - dividing integumentary tissue. They are able to actively divide and produce hairs and reproductive organs. Real hairs are located on the surface of the meristoderm scattered or in bundles and are often immersed with their bases in special depressions - cryptostomes. Deeper under the meristoderm lies a cortex of larger stained cells. In the central colorless part of the thallus, two groups of cells can be distinguished. In the center there are loosely or densely arranged threads with strongly elongated cells - the core, large colorless cells - the intermediate layer lie between the core and the bark. The core of brown algae serves not only to transport the products of photosynthesis, but also performs a mechanical function; it often contains thin filaments with thick longitudinal sheaths. Representatives of the order Laminariales differ in the most complex anatomical structure, in which mucous channels develop in the core with special secretory cells for transporting photosynthesis products - sieve tubes and tubular filaments.

The thalli of brown algae are attached to the ground or other substrates and only occasionally, due to mechanical damage, break off and float freely. Attachment organs are usually long outgrowths - rhizoids, in large forms they are massive and are short root-like outgrowths covering the substrate like bird claws. In representatives of the order Fucales and some other algae, the attachment organ is a disc-shaped growth at the base of the thallus - a basal disc, flattened or conical, tightly adhering to the ground.

Branching of brown algae is monopodial. Lateral branches alternate, scattered or opposite. With their rapid growth to the size of the main thread (mother cells), dichotomous branching occurs. Quite often, alternate and opposite branches are located in the same plane and the algae acquire a peculiar pinnate appearance. The correct placement of branches is often masked by secondary branches.

Among brown algae there are species with ephemeral, annual and perennial thalli. The duration of the existence of thalli is greatly influenced by environmental conditions. Perennial thalli of brown algae are of several types. In some algae, the thallus is perennial, every year only the shoots on which the reproductive organs (Fucales) developed, while in others (Laminariales) the trunk and attachment organs are perennial, the lamellar part is annual. In some tropical species of Sargasso algae, only a disk is perennial, which serves to attach the thallus.

Brown algae cells are mononuclear, spherical, ellipsoid, barrel-shaped, mostly cylindrical, elongated or short-cylindrical, disc-shaped, sometimes polygonal or indefinite. They also vary in size. The nucleus is of the usual type for eukaryotes.

The cell wall is bilayered. The inner layer is cellulose, but the cellulose of brown algae differs in its properties from the cellulose of flowering plants and therefore it is sometimes called algulose. The outer layer of the shell is pectin, usually consisting of protein compounds of alginic acid and its salts. Due to this structure, the shell of brown algae can swell strongly, turning into a mucous mass, sometimes of a significant volume. In most brown pectin, the basis of pectin is a gum-like substance - algin (soluble sodium salt of alginic acid), in some - fucoidin.

The contents of neighboring cells of brown algae are communicated through plasmodesmata. In cells with thick membranes (in large thalli), pores are well expressed.

Brown algae cells have one large or several small vacuoles. In addition, there are physodes - very small vacuoles (up to 4 microns in diameter) filled with fucosan - a compound similar to tannin. In young cells, the physodes are colorless, in old cells they are colored yellow or brown.

Chloroplasts are parietal, mostly numerous, small, disc-shaped, less often ribbon-like or lamellar. However, as cells age, the shape of chloroplasts may change, and instead of narrow ribbon-like curved cells, numerous disc-shaped chloroplasts may appear. Pyrenoids are present either in the chloroplasts of vegetative cells or only in the chloroplasts of gametes; in a number of species, pyrenoids are absent or rare.

Brown algae are distinguished by a peculiar complex set of pigments. In chloroplasts, chlorophylls a, c (chlorophyll b is absent), β- and ε-carotenes, as well as several xanthophylls - fucoxanthin, violaxanthin, antheraxanthin, zeaxanthin, etc. were found. Fucoxanthin of intense brown color is especially specific among them. Different ratios of these pigments determine the color of brown algae from olive-yellowish to dark brown, almost black.

The assimilation products of brown algae are various carbohydrates soluble in cell sap - kelp (polysaccharide), mannitol (a six-hydric alcohol that plays a significant role in metabolism), as well as oil.

Brown algae have asexual and sexual forms of reproduction. However, vegetative propagation by fragmentation of the thallus cannot be considered unconditional. It is observed only when the torn thalli fall into more or less protected places and continue their vegetation there. At the same time, their lower older parts die off, collapse, and young branches develop into independent plants, which, however, are not attached to the ground. Such plants, floating or lying on the ground, never form organs of sexual and asexual reproduction.

Special buds for vegetative reproduction are found only in species of the genus Sphacelaria Lyngb. (Fig. 18.3).

Asexual reproduction is carried out by mobile zoospores, which are formed in large quantities in one-celled sporangia. In the most simply organized marine and freshwater brown algae (Ectocarpus, Sphacelaria, Pleurocladia A. Br., etc.), single-celled sporangia are spherical or ellipsoid cells that are located as lateral outgrowths of branches (Fig. 18.4, 1). In sporangia, a reduction division of the nucleus occurs, followed by multiple mitotic divisions; chloroplasts divide simultaneously with the nuclei. As a result, a large number of zoospores are formed, which are released through a rupture of the membrane at the top of the sporangium and, after swimming for a short time, germinate into a new, similar in appearance, but already haploid plant. In species of the genus Laminaria, zoosporangia form sori on the surface of the leaf-shaped plate. The sorus consists of paraphyses and zoosporangia (see Fig. 18.4, 2, 5). Paraphyses are elongated cells, with chloroplasts at the upper expanded end, developing on the surface of the thallus between the reproductive organs and serving to protect them. The shell of the paraphysis at the top is strongly mucilaginous, forming a kind of thick mucous cap. Mucous caps of adjacent paraphyses close, resulting in a continuous thick layer of mucus that protects the sorus. Zoosporangia are elongated ellipsoid, with a mucoid membrane at the top. Depending on the species, it develops in zoosporangia by 16-128 zoospores. The first division of the nucleus is reduction. Some brown algae reproduce by immobile, devoid of flagella, spores - aplanospores. Monospores are observed only in species of the order Tilopteridales, tetraspores - in species of the order Dictyotales (Dictyota dichotoma (Huds.) Lamour., see Fig. 18.4, 4).

The sexual process is iso-, hetero- and oogamous. Gametes are usually produced in multilocular gametangia, one in each chamber. Motile cells of brown algae - zoospores into gametes - have a similar structure - they are pear-shaped, with one chloroplast and two flagella attached to the side. One flagellum is longer, pinnate, directed forward, the other is shorter, smooth, flagellate, directed backward. Stigma in motile cells is not always noticeable. The chloroplast of male gametes in oogamy may be colorless.

In the development cycle of most brown algae of the Phaeozoosporophyceae class, there is a change in development forms and alternation of sexual and asexual generations, i.e. gametophyte (sometimes also gametosporophyte, if the same organism can give rise to zoospores and gametes) and sporophyte.

These processes are detailed in Section 3.2.3. Here we dwell only on some features of the development cycles of brown algae. In the most primitive marine brown algae of the order Ectocarpales, an isomorphic change in developmental forms is observed, but there is still no strict alternation of generations. The spores produced by the sporophyte can develop into both gametophytes and sporophytes.

The correct isomorphic change of forms of development is observed in representatives of the order Dictyotales. The most widespread of these is Dictyota dichotoma (Huds.) Lam., which has a forked thallus with flat, usually in the same plane branches without a longitudinal rib (Fig. 18.5).

Algae of the order Laminariales have a heteromorphic change in developmental forms with the obligatory alternation of sporophytes and gametophytes. Their development cycle is characterized by the correct change of a powerful sporophyte and a microscopic, simply arranged gametophyte.

Brown algae that do not have a change in development forms, but only a change in nuclear phases, include representatives of the families Fucaceae, Cystoseiraceae and Sargassaceae. Their normal reproduction is possible only sexually. The sexual process is a typical oogamy. Sexual organs develop in conceptacles (Fig. 18.6). Long hairs grow from the wall of the conceptula - paraphyses, filling almost its entire cavity. Particularly long hairs develop in female conceptacles, where they protrude in the form of a bundle from the opening of the conceptacle. Among these hairs, oogonia and antheridia develop (Fig. 18.7, 1-5). Antheridia are formed in large numbers at the ends of special single-row branched branches growing from the wall of the conceptacle. Two layers are distinguishable in their shell. When the antheridium matures, its outer shell bursts and the antherozoids come out in the form of a package surrounded by an inner shell. In sea water, the inner shell is torn and pear-shaped antherozoids with a large nucleus and orange stigma are released. The oogonia are spherical or ellipsoid, equipped with a three-layered membrane, located in conceptacles on a short unicellular stalk. In the oogonium, 8 eggs are formed, they enter the water, surrounded by two inner layers of the oogonium membrane. When the eggs are completely freed from the shells of the oogonium, fertilization occurs. A fertilized egg develops its own thick shell and immediately begins to germinate, forming a new fucus thallus.

In freshwater brown algae, developmental cycles have not been studied.

There are some differences in views on the classification of brown algae. According to a number of researchers, the Phaeophyta division is divided into 2 classes: Phaeozoosporophyceae and Cyclosporophyceae. Brown algae belong to the Cyclosporaceae, in which the reproductive organs develop in conceptacles and are large in size, allowing them to be seen on preparations with the naked eye. All other brown algae are classified as pheozoospores, many of which reproduce by zoospores. Since the 1930s, there has been a tendency to classify brown algae depending on the characteristics of development cycles. At the same time, it was proposed to divide brown algae into 3 classes: Isogenerate, Heterogenerate, Cyclosporae. The proposed classification has received a very wide distribution. However, the division of brown algae into isogenerate and heterogeneous is rather arbitrary, since in both classes, in separate orders, there are representatives with the opposite type of change in developmental forms. Adhering to the views of domestic algologists, we adopt a classification scheme for dividing brown algae into 2 classes - Phaeozoosporophyceae and Cyclosporophyceae.

The question of the origin of brown algae is still poorly developed. A. Sherfell associated their origin with golden (Chrysophyta). According to A. Pasher, there is a phylogenetic relationship between brown and cryptophytic (Cryptophyta). The peculiar structure of the flagella, together with the brown coloration, allowed M. Shadefoe to combine into one large division of Chromophycophyta such large taxa as Pyrrhophyta (where, in addition to peridines, he included cryptophyte and euglena algae), Chrysophyta (to which he included, in addition to golden, yellow-green and diatoms algae) and Phaeophyta. According to biochemical properties, of all brown-colored organisms, diatoms are closest to brown algae. It is diatoms and brown algae that are characterized by such common pigments as chlorophyll (also characteristic of peridineans), fucoxanthin (also found in golden algae) and neofucoxanthins A and B. Taking into account the presence of a number of similarities between diatoms, golden algae and brown algae, we join the thought expressed by a number of scientists about the possibility of their origin from close, if not common, monadic ancestors.

According to G. Papenfuss, the original order of brown algae is Ectocarpales. The parenchymal structure of the thallus, apical growth, the oogamous sexual process, and the heteromorphic change in development forms in different groups of brown algae developed independently of each other.

Marine brown algae are widespread in all seas of the globe. Their thickets are common in the coastal waters of Antarctica and the northern islands of the Canadian Arctic Archipelago. They reach their greatest development in the seas of temperate and subpolar latitudes, where, due to the low temperature and high concentration of nutrients, the most favorable conditions for their vegetation are created. Brown algae populate vertically all horizons of the shelf. Their thickets are found from the littoral zone, where they are out of water for hours at low tide, to a depth of 40-100 (200) m. And yet, the most dense and extensive thickets of brown algae are formed in the upper part of the sublittoral to a depth of 6-15 m. In these places, with sufficient illumination, there is a constant movement of water caused by surf and surface currents, which, on the one hand, ensures an intensive supply of biogenic substances to the thalli, and, on the other hand, limits the settlement of herbivorous animals.

Usually brown algae live on rocky or rocky soils, and only in calm places near the coast or at great depths can they stay on the valves of large mollusk shells or on gravel. Torn off thalli are carried by the current to calm places with a muddy or sandy bottom, where they continue to vegetate under sufficient illumination. Species with air bubbles on the thallus, when separated from the ground, float to the surface of the water, forming large clusters (Sargasso Sea). Among marine brown algae, there are a significant number of epiphytic and endophytic forms.

In the seas of temperate and subpolar latitudes, brown algae reach their maximum development in the summer months, although the rapid growth of their thalli begins in early spring, when the water temperature approaches 0°C. In tropical seas, the mass development of brown is confined to the winter months, when the water temperature drops slightly. Some types of marine brown algae can be found in heavily desalinated areas of the seas with a salinity of less than 5‰.

The role of brown algae in nature is extremely large. They are one of the main sources of organic matter in the coastal zone, especially in the seas of temperate and subpolar latitudes, where their biomass can reach tens of kilograms per 1 m2. In addition, thickets of brown algae serve as breeding, sheltering and feeding grounds for many coastal animals; they also create conditions for the settlement of microscopic and macroscopic algae of other systematic groups.

The economic importance of brown algae is also great, especially as a raw material for obtaining various kinds of substances (for example, alginates - salts of alginic acid, in particular sodium alginate). This substance is widely used to stabilize various solutions and suspensions. The addition of a small amount of sodium alginate improves the quality of food products (canned food, ice cream, fruit juices, etc.), various coloring and adhesive substances. Alginates are used in book printing, in the production of plastics, synthetic fibers and plasticizers, to obtain weather-resistant coatings and building materials. They are found in high quality machine lubricants, dissolvable surgical sutures, ointments and pastes in the pharmaceutical and perfume industries. In the foundry, alginates are used to improve the quality of foundry earth. Alginates are used in the production of electrodes for electric welding, which make it possible to obtain higher quality seams. Brown algae is also used as a raw material for the production of mannitol, which is used in the pharmaceutical industry, in the food industry - for the manufacture of diabetic foods, and in the chemical industry - in the production of synthetic resins, paints, paper, explosives, and leather dressing. Brown algae contain a large amount of iodine and other trace elements, so they are used in the preparation of fodder meal. In fresh and processed form, they are used as fertilizers.

Brown algae have been used in medicine since ancient times. Now more and more new areas of their application are being identified, for example, for the manufacture of blood substitutes, for the preparation of drugs that prevent blood clotting and promote the removal of radioactive substances from the body. Since ancient times, brown algae (mainly representatives of the order Laminariales) have been eaten by humans.

The negative properties of brown algae include their participation, together with other organisms, in the fouling of ships, buoys, and various hydraulic structures submerged in water, which worsens their performance.

The intensive use of wild-growing marine macrophytes, in particular brown algae, has led to the depletion of their natural reserves and has confronted mankind with the need for their artificial cultivation. Therefore, in the last 30 years, aquaculture of algae has developed significantly. In Norway and the UK, not only are species of the genus Laminaria successfully cultivated, but the technology of their production is also being improved. In France, work is underway to acclimatize representatives of the genus Macrocystis. Seaweed aquaculture is intensively developing in the USA. In this case, special attention is paid to Macrocystis pyrifera. In the USSR, research is being carried out on the artificial breeding of Laminaria saccharina (L.) Lam. in the White Sea. Thus, the cultivation of seaweed is becoming industrial in nature and is becoming an increasingly profitable branch of crop production, despite some economic and environmental difficulties.

In fresh waters of temperate latitudes, 5 species of brown algae from the Phaeozoosporophyceae class were found: Bodanella lauterbornii Zimmerm. (order Ectocarpales, family Ectocarpaceae) (Fig. 18.8, 1), Pleurocladia lacustris A. Br. (order Chordariales, family Myrionemataceae) (Fig. 18.8, 2). Heribaudiella fluviatilis (Aresch.) Sved. (order Chordariales, family Lithodermataceae (Fig. 18.8, 3)), Streblonema longiseta Arnoldi (order Chordariales, family Streblonemataceae) (Fig. 18.8, 4). Sphacelaria fluviatilis Jao (order Sphacelariales, family Sphacelariaceae) (Fig. 18.8, 5).

Ecological group and living conditions

The department of brown algae (Phaeophyta) has about 1500 species.

Brown algae live almost exclusively in the seas(only a few species are found in fresh water bodies). Relatively shallow depth, for most species - 5-15 m, but some species are common to a depth of 40-100 m and even 200 m. Brown algae are included in ecological group of benthic(bottom) organisms.

The structure of brown algae

The precursors of brown algae chloroplasts are bacteria close to Heliobacterium chlorum. The main photosynthetic pigment is chlorophyll a, the auxiliary ones are carotenoids, including brown fucoxanthin and yellow xanthophylls. Auxiliary pigments of brown algae expand the spectrum of light absorbed by them in the blue-green region.

Spare material - starch-like soluble carbohydrate kelp.

Thallus (thallus) - only multicellular. Large, sometimes multi-meter thalli of brown algae are kept afloat thanks to air bubbles located in the thallus. In many representatives of brown algae, tissue differentiation has been outlined. Inside the thallus pass vascular bundles resembling the phloem of higher plants. The appearance of the vascular system is associated with the need to transport nutrients to a multi-meter thallus - from the upper, photosynthetic, parts of the plant to the lower, in which the conditions for photosynthesis are worse.

Rice. The structure of brown algae

reproduction

In brown algae, there are all forms of sexual reproduction - isogamy, heterogamy and oogamy. There is an alternation of generations, usually heteromorphic. Asexual reproduction - zoospores and pieces of thallus (vegetative reproduction).

The value of brown algae

Brown algae form entire "underwater forests" at a relatively shallow depth, the coasts of all the seas and oceans of both hemispheres surrounding with a solid wall. These "underwater forests" provide food, shelter, and breeding grounds for a vast array of marine life, including many game fish. After dying, the algae form detritus, which is food for planktonic organisms.

Brown algae are ubiquitous, but the largest species are found in the seas of temperate and northern latitudes.

Rice. 1. Brown algae: a) macrocystis (Macrocystus); c) sargassum (Sargassum); c) fucus (Fucus); d) kelp (Laminaria)

Typical representatives of the department

Brown algae is widespread in the Far Eastern seas. kelp (seaweed), the length of the thallus is 5-6 m. Laminaria is used as food by the peoples of Southeast Asia.

Giant brown algae found on the Pacific coast of South America macrocystis. Its huge thallus reaches a length of 50-60 m. It is interesting that it grows in just one season.

On the littoral (exposed at low tide part of the bottom) of the northern seas, extensive thickets form fucus(thallus length up to 2 m).

The South Atlantic (Sargasso Sea) is characterized by huge accumulations of brown algae sargassum."Sargasso" in Spanish means "grapes", and indeed, the groups of air bubbles that keep the thallus of these algae afloat resemble bunches of grapes. Sargassum species living in the Sargasso Sea are the only brown algae that float on the surface of the water, and are not attached to the bottom.

Economic importance

Brown algae cells are covered over a cellulose shell with a layer of a special carbohydrate - pectin, consisting of alginic acid or its salts (alginates). When mixed with water (at a ratio of 1:300), alginates form a viscous solution.

Alginates are used extremely widely:

• in the food industry (when receiving marmalades, juices, marshmallows, etc.);
• in perfumery (manufacturing of creams, pastes, gels, etc.);
• in medicine and the pharmaceutical industry (in the manufacture of ointments, pastes, soluble surgical threads);
• in the chemical industry (in the production of varnishes, paints, adhesives that do not lose their qualities during freezing and thawing; plastics, plasticizers, synthetic fibers);
• in typography (to improve print quality);
• alginates make natural fabrics colorless and waterproof, they are used to improve the quality of molding earth in foundry, for the manufacture of electrodes (improving the quality of welds) and in many other sectors of the economy.

Hexahydric alcohol is obtained from brown algae mannitol, used as a blood substitute, as a medicine in the treatment of diabetes, as well as in light and chemical industries (in the production of paper, varnishes, paints, explosives and leather dressing).

Brown seaweed kelp (seaweed) is consumed into food.

Brown algae are used and how medicine: as a mild laxative, in the treatment of vascular diseases, as well as a source of iodine and trace elements in diseases of the thyroid gland. Iodine was first obtained from brown algae, and in the past they were the main raw material for its production. Currently, the scale of this production has been sharply reduced due to the emergence of more cost-effective sources of iodine.

Brown algae can be used as indicators of gold deposits, because they are able to accumulate it in the cells of the thallus.

Brown algae are also used in agriculture - as fertilizer And for livestock feed.