Hydrobiology

HYDROBIOLOGY (from the Greek hydor - water, bios - life, and logos - science), a branch of biology that studies the way of life of organisms in relation to the conditions of the aquatic environment. - Principal stages of development. Hydrobiology as an independent scientific discipline with its own special research methods is a comparatively young science, the main tasks of which were first formulated in 1880 in the famous book by Professor Semper, «Natürliche Existenzbedingungen der Tiere». But even before hydrobiology was established as an independent discipline, zoologists and botanists accumulated a vast amount of material on the anatomy, developmental history, systematics, and geographical distribution of marine forms. Although most of these facts were obtained without strict consideration of their relation to the aquatic environment, these facts nevertheless represent a huge capital that hydrobiology also makes extensive use of. The very rapid development of hydrobiology was facilitated, on the one hand, by the establishment of marine and freshwater biological stations (foremost among which should be placed the Naples Zoological Station founded by A. Dohrn in 1870), and on the other hand, by the equipment of major deep-sea expeditions. From 1872 to 1876, the British expedition on the ship Challenger, led by C. Wyville Thomson, gathered immense material on the marine fauna and at the same time definitively proved the presence of life at all depths, down to the depth of 9,644 meters known at that time. The hydrobiological study of fresh waters began in 1874, when F.-A. Forel first studied Lake Geneva in detail and discovered in it a deep-water fauna, partly consisting of glacial period relics. Completely unexpected and extremely interesting adaptations (luminous organs, telescope eyes, absence of eyes, long tentacles, and many others) of deep-sea inhabitants (see Biological analysis) to the peculiar conditions of their surrounding environment, which became known thanks to a series of expeditions (besides the aforementioned Challenger expedition, the French on the ship Talisman, the American on the ship Albatross, and especially the German on the steamer Valdivia in 1898-1899, led by C. Chun), are the object of research of hydrobiologists of the late 19th and early 20th centuries. These expeditions provided inexhaustible material for studying the morphology of animals and plants and the adaptations in their organization for various conditions of their life in water, as well as for distribution in both horizontal and vertical directions. One of the results of these studies is the establishment of the so-called bipolarity of marine forms. The essence of this phenomenon is that a whole series of organisms is found only in the arctic and antarctic zones and nowhere in between. An explanation of the cause of this phenomenon was given by Pfeffer (1891), who proved that this peculiar distribution is a consequence of both geological climate changes and the temperature distribution in the ocean. A new era in hydrobiology was created by the methods developed by V. Hensen and his school (Lohmann, Apstein) for the quantitative and qualitative study of plankton, by which Hensen understands "everything that is carried in the water," in contrast to organisms attached to or moving along the bottom (benthos), and those that independently move about in the water ("nekton," according to Haeckel). The study of plankton became the center of attention for hydrobiologists starting in 1889. In that year, led by Hensen, a plankton expedition worked on studying both the distribution and the qualitative and quantitative composition of plankton in the Atlantic Ocean. The determination of the quantities of planktonic organisms played a huge role in the study of the biology of small organisms (algae, crustaceans, mollusks, etc.), because it made it possible to study their distribution not only in vertical but also in horizontal directions, their daily migration, etc. These methods also played a huge role in practical terms, because they made it possible to determine the amount of living protein matter in a given volume of water of a given basin or, in other words, to determine its food supply for fish and other commercial aquatic animals. The study of nekton, which includes most fish, as well as aquatic mammals such as whales, dolphins, and seals, began much earlier, mainly from the 1850s (Kessler, Baer, and Danilevsky). In view of the great economic importance of fisheries and the reduction in the quantity of the most important commercial fish observed for some time, in 1902 the states located along the Northern European seas (England, Germany, Belgium, Denmark, Holland, Norway, Sweden, Russia) united and organized the "International Council for the Exploration of the Sea." Through the labors of this "Council," the life (especially fish) of these seas has been investigated in extreme detail. - Starting from 1911, the quantitative research method was extended to the benthos population, since from this time C. G. J. Petersen began using a bottom grab (see Biological analysis), which makes it possible to determine the population density of a defined area of the bottom. Modern tasks of hydrobiology. - The main task of hydrobiology is the study of the influence of the aquatic environment on the organization of organisms living in it and the regularities according to which the colonization of water spaces takes place (Lohmann). The division of hydrobiology into freshwater and marine, pure and applied, is caused by practical convenience in the arrangement of material rather than essential differences in the methods and tasks of research. According to method and tasks, hydrobiology is divided (Hentschel) into three branches: monobiotics (the influence of the environment on individual individuals or species), cenobiotics (the influence of the environment on individual communities), and holobiotics (the influence of the environment on the distribution of organic life as a whole in the aquatic environment). - Monobiotics has the task of elucidating both the morphological and physiological properties of individual individuals depending on the properties of water (its salinity, gases, light, heat, pressure), and the influence of the same factors on the life of entire species (respiration, nutrition, reproduction, and development). Thus, under the influence of different salt concentrations, the shape of organisms changes. Schmankewitsch in the 1870s described changes in body shape in the crustacean Artemia salina resulting from the exposure of the crustaceans to water of varying salinity. Recent experiments repeated by Gaievskaja showed that these crustaceans are indeed extremely adapted to changes in environmental conditions and react to them by changing their body shape. Detailed studies of certain bodies of water in northern Europe have shown that organisms of non-local origin are frequently found in them, representing relics (marine or glacial) or immigrants, i.e., those that actively penetrated here. Sven Ekman showed that a number of such marine relics (Mysis relicta, Chiridota entomon, Limnocalanus grimaldii) differ morphologically and biologically from their closest relatives living in the seas. Along certain rivers (Volga, Don, Dnieper, Danube), such marine immigrants as the mollusk Dreissensia polymorpha and the crustacean Corophium curvispinum penetrated, attached to ships, into the upper reaches of these rivers, and through canals - even into neighboring basins, into the rivers of the Baltic and German Sea basins. - The nutrition of aquatic organisms represents one of the main problems of hydrobiology. There are valuable data on the composition, methods of intake, and utilization of food. The main food of aquatic animals is plants and animals of various forms and their decay products taken by them from the outside (Lohmann, Woltereck, and others). In addition, however, organic substances dissolved in water, taken in by the entire surface of the animal's body (Pütter, and recently Krizenecký and others), apparently also play some role in nutrition, but they are only an auxiliary and not the sole type of nutrition. Cenobiotics, or the study of the influence of the environment on entire societies or biocenoses, in other words - the comparative study of the action of the environment on a number of organisms existing under the same conditions. The result of the environmental action is found in the phenomena of convergence, namely, in the formation of identical adaptations for the same purposes in completely different groups. Such convergent phenomena must be considered, for example, the formation of identical adaptations in different groups of animals. Thus, the formation of fat inclusions makes it possible to stay suspended (the medusa Physalia, the radiolarian Sphaerozoum). Water striders (Hemiptera) and water spiders living on the water surface actively move thanks to the fact that their thin limbs with tufts of hair at the end are not wetted by water. In various inhabitants of plankton, remarkable adaptations to life in a suspended state are found. Almost all of them are transparent and, moreover, ranging from algae to fish eggs and larvae, are equipped with one or another adaptation by means of which they are held in the water. At the same time, it is observed that, depending on the internal friction of water, its "viscosity" (which, as is known, changes depending on the temperature and chemical composition of the water), the shape of the given planktonic organism also changes.

Ostwald gave the following formula: sinking velocity = residual weight / (form resistance × internal friction of water); that is, with an increase in the relative surface area of an organism, a drop in temperature, or an increase in salinity, the ability of a given organism to "soar" increases, and vice versa. The study of the life of aquatic communities, or biocenoses, also belongs to this branch of hydrobiology. As early as 1877, Möbius described the biocenosis of oyster banks. At the present time, the biocenoses observed in various aquatic biotopes are being studied very intensively (see Biocenosis). The dependence of biocenoses on environmental conditions has been established. Much attention is paid to the active reaction of water, represented as the concentration of hydrogen ions (see), which depends chiefly on the content of carbonates, CO₂, and humic acids in the water (Breslau, Atkins, Skadovsky). For certain planktonic biocenoses, the fact of daily migrations depending on light has been established (Ruttner). The active transition of certain representatives of the nekton, chiefly fish, from the sea to rivers is of great interest to hydrobiologists. The benthos population breaks down into a number of biocenoses, depending on bottom composition, depth, and water movement. In each of the biocenoses, various kinds of adaptations to the environment are found. Peculiar biocenoses are observed on various objects located in the water (ships, piles, etc.). The organisms making up these fouling communities are adapted to sharp movements of water and require a high oxygen content in the water for their existence. The biocenoses of the water surface are adapted to life in the surface film of water (the so-called "neuston": various algae, protozoa, etc.) and to swimming in the surface layer of water—the medusae Physalia, Velella, the plants Lemna, Salvinia, and others (the so-called "pleuston"). Holobiotics, or the doctrine of the general distribution of life in water. This branch studies the distribution of individual specimens of the same species, the distribution of species and biocenoses, the distribution of organisms by habitat (sea, open ocean, coasts, standing waters, etc.), and the zoogeographical distribution of marine forms. In limnology recently, much work has been devoted to the study of the so-called typology of lakes. Thienemann and Naumann distinguish eutrophic (rich in nutrients, abundant plankton, insignificant O₂ content at the bottom, chironomid larvae [dipterans] of the Chironomus plumosus and Chironomus liebeli-bathophilus type), oligotrophic (poor in nutrients, insignificantly developed plankton, more or less uniform distribution of O₂, chironomid larvae of the Tanytarsus type), and dystrophic (rich in humic substances, poor and peculiar plankton, larvae of the Chironomus plumosus type). The distribution of our water bodies according to these types of Thienemann and Naumann and the establishment of new peculiar types constitutes the subject of research of many hydrobiologists of the USSR. In the seas, much attention is paid to the metabolism studies undertaken by Hensen and still successfully conducted by Brandt today. The relationship between the entire aggregate of plankton, nekton, etc., i.e., the entire production of a given water body, is being clarified. In the USSR, most work has recently been done in the study of the northern seas (White, Barents, Arctic Ocean), the Black, Caspian, and Aral seas, the lakes Baikal, Ilmen, Glubokoye, Kosino, and others, and the rivers Volga, Dnieper, and others. Applied Hydrobiology. Application of hydrobiology to medicine. Since the work of Grassi (see), it has been known that the malaria plasmid, the causative agent, is transmitted by various species of mosquitoes, the larvae of which are aquatic inhabitants. Naturally, combatting these mosquitoes is possible only on the condition of knowing their biology. Thanks to the joint work of entomologists, physicians, and hydrobiologists at the present time in the West and in America, in most countries, the danger of malaria infection has been more or less weakened. Strong malaria epidemics in 1922–1923 in the USSR also drew the attention of hydrobiologists. In various regions of the USSR, tropical institutes, malaria stations, and hydrobiological stations studied the structure and lifestyle of mosquitoes in great detail. In tropical and some southern countries, various fishes (chiefly Girardinus poeciloides, Gambusia affinis, as well as carps) are successfully used to destroy mosquito larvae (see Malaria). Among other dipterans, hydrobiologists study blackflies (Enderlein, Wilhelmi), which harm our livestock industry chiefly, and biting midges (Ceratopogonidae), the bite of which, like the bite of mosquitoes, is very painful. Parasites of humans and animals inhabiting aquatic animals at various stages of their development are studied in detail by hydrobiologists. The life of the embryos of the liver fluke (Fasciola hepatica) in the mollusk Limnaea truncatula, the guinea worm (Fuellebornius medinensis) in cyclopes, the blood fluke (Schistosomum haematobium) in the mollusks Bullinus contortus and others, the procercoid of the broad tapeworm (Diphyllobothrium latum) in Cyclops strenuus and Diaptomus gracilis, and its plerocercoid in various fishes and many others has been clarified recently. Hydrobiological studies of drinking and sewage waters also belong here (see also Biological analysis, Biological method of sewage purification). Application of hydrobiology to agriculture. Fisheries and fish farming: the lifestyle, nutrition, reproduction, migrations, etc., of fish of commercial importance, methods of artificial fish breeding, the use of irrigated fields (chiefly rice fields) for fish breeding, land reclamation of ilmens and other water areas—all these are works which in a significant part are carried out by hydrobiologists. Teaching. Scientific teaching of hydrobiology is concentrated in universities and higher agronomic schools. Abroad, special courses are taught in a number of universities (Copenhagen, Kiel, Königsberg, Leipzig, University of Michigan in Ann Arbor, Illinois in Urbana, etc.) and there are special hydrobiological departments at all higher schools with a fisheries department. In Russia, the first special department of hydrobiology was opened in 1914 at the fisheries department of the Petrovsk (now Timiryazev) Agricultural Academy in Moscow (Prof. S. A. Zernov). Before this time, only isolated courses on limnology, planktology, etc., were taught in various higher educational institutions. Recently, special cycles of hydrobiology with separate courses (hydrobiology, plankton, benthos, life of seas, etc.) have been opened at the physics and mathematics faculties in Moscow, Leningrad, and some others. In addition, courses on hydrobiology are conducted during the summer practice of students at biological stations. Institutes and societies. At the present time, in all cultured countries, there are special hydrobiological institutes and stations. The Naples Station in Italy (founded in 1870), the English one in Plymouth (founded in 1888), the American one in Woods Hole (founded in 1888), and the Heligoland one in Germany (founded in 1892), at which more than a hundred scientists work annually, are the most famous. In the USSR, hydrobiological research is currently conducted by 46 scientific institutions of various types, separately specially equipped expeditions, and some biological departments of higher educational institutions. Hydrobiological institutes conduct work: 1) purely scientific (hydrobiological studies of water bodies), 2) applied (sanitary assessment of water, aquatic insects transmitting various diseases, fisheries and fish farming, etc.), 3) educational and enlightening (practice for higher education students, courses and lectures, museums, exhibitions, etc.). Scientific hydrobiological societies and associations exist in a number of countries. Researchers of inland water bodies are united by the International Society of Theoretical and Applied Limnology, the fourth congress of which took place in 1925 in the USSR. In the USSR, starting from 1924, All-Union hydrological congresses have been convened; in Moscow, there is a society of researchers of water and its life. Most hydrobiological institutions and all societies publish their proceedings and journals.