How deep does the zone of photosynthesis extend in the oceans? Efficiency of photosynthesis in terrestrial and marine ecosystems. Cyanobacteria are able to “short” the process of photosynthesis In which zone of the ocean is photosynthesis impossible

Charles

Why do the oceans have "low productivity" in terms of photosynthesis?

80% of the world's photosynthesis takes place in the ocean. Despite this, the oceans also have low productivity - they cover 75% of the earth's surface, but from the annual 170 billion tons of dry weight recorded through photosynthesis, they provide only 55 billion tons. Do not these two facts, which I encountered separately, contradict? If the oceans fix 80% of the total C O X 2 "role="presentation" style="position: relative;"> CO X C O X 2 "role="presentation" style="position: relative;"> C O X 2 "role="presentation" style="position: relative;"> 2 C O X 2 "role="presentation" style="position: relative;"> C O X 2 "role="presentation" style="position: relative;">C C O X 2 "role="presentation" style="position: relative;">O C O X 2 " role="presentation" style="position: relative;">X C O X 2 "role="presentation" style="position: relative;">2 fixed by photosynthesis on earth and releases 80% of the total O X 2 "role="presentation" style="position: relative;"> O X O X 2 "role="presentation" style="position: relative;"> O X 2 "role="presentation" style="position: relative;"> 2 O X 2 "role="presentation" style="position: relative;"> O X 2 "role="presentation" style="position: relative;">O O X 2 " role="presentation" style="position: relative;">x O X 2 "role="presentation" style="position: relative;">2 Released by photosynthesis on Earth, they must also have been 80% of the dry weight. Is there a way to reconcile these facts? In any case, if 80% of photosynthesis takes place in the oceans, it hardly seems low productivity - then why are the oceans said to have low primary productivity (multiple reasons are also given for this - that light is not available at all depths in the oceans, etc.)? More photosynthesis should mean more productivity!

C_Z_

It would be helpful if you point out where you found these two statistics (80% of the world's productivity is in the ocean and the oceans produce 55/170 million tons of dry weight)

Answers

chocoly

First, we must know what are the most important criteria for photosynthesis; they are: light, CO2, water, nutrients. docenti.unicam.it/tmp/2619.ppt Second, the productivity you are talking about should be called "primary productivity" and is calculated by dividing the amount of carbon converted per unit area (m2) by the time. ww2.unime.it/snchimambiente/PrPriFattMag.doc

Thus, due to the fact that the oceans cover a large area of ​​the world, marine microorganisms can convert a large amount of inorganic carbon into organic (the principle of photosynthesis). The big problem in the oceans is the availability of nutrients; they tend to deposit or react with water or other chemicals, even though marine photosynthetic organisms are mostly found on the surface, where of course light is present. This reduces as a consequence the potential for photosynthetic productivity of the oceans.

WYSIWYG ♦

M Gradwell

If the oceans fix 80% of the total CO2CO2 fixed from land photosynthesis and release 80% of the total O2O2 released from land photosynthesis, they should also account for 80% of the dry weight produced.

First, what is meant by "O 2 released"? Does this mean that "O 2 is released from the oceans into the atmosphere, where it contributes to the growth of surpluses"? This cannot be, since the amount of O 2 in the atmosphere is fairly constant, and there is evidence that it is much lower than during Jurassic times. In general, global O 2 sinks should balance O 2 sources, or if something should slightly exceed them, causing current atmospheric CO2 levels to gradually increase at the expense of O 2 levels.

Thus, by "released" we mean "released during photosynthesis at the time of its action."

The oceans fix 80% of the total photosynthesis-bound CO2, yes, but they also break it down at the same rate. For every algae cell that is photosynthetic, there is one that is dead or dying and consumed by bacteria (which consume O2), or it itself consumes oxygen to maintain its metabolic processes during the night. Thus, the net amount of O 2 emitted by the oceans is close to zero.

Now we have to ask what we mean by "performance" in this context. If a CO 2 molecule is fixed due to algae activity, but then almost immediately becomes unfixed again, is this considered "performance"? But blink and you'll miss it! Even if you don't blink, it's unlikely to be measurable. The dry weight of the algae at the end of the process is the same as at the beginning. so if we define "productivity" as "increase in dry weight of algae", then productivity will be zero.

For algae photosynthesis to have a sustained effect on global CO 2 or O 2 levels, the fixed CO 2 must be incorporated into something less fast than algae. Something like cod or hake, which as a bonus can be collected and put on the tables. "Productivity" usually refers to the ability of the oceans to replenish these things after the harvest, and it's really small compared to the land's ability to produce repeat crops.

It would be a different story if we viewed algae as potentially mass-harvesting, so that their ability to grow like wildfire in the presence of fertilizer runoff from the ground was seen as "productivity" rather than a profound inconvenience. But it's not.

In other words, we tend to define "productivity" in terms of what is beneficial to us as a species, and algae is generally useless.

Photosynthesis underlies all life on our planet. This process, which takes place in land plants, algae and many types of bacteria, determines the existence of almost all life forms on Earth, converting sunlight into chemical bond energy, which is then transferred step by step to the tops of numerous food chains.

Most likely, the same process at one time initiated a sharp increase in the partial pressure of oxygen in the Earth's atmosphere and a decrease in the proportion of carbon dioxide, which ultimately led to the flourishing of numerous complexly organized organisms. And until now, according to many scientists, only photosynthesis is able to restrain the onslaught of CO 2 emitted into the air as a result of the daily burning of millions of tons of various types of hydrocarbon fuels by humans.

A new discovery by American scientists forces us to take a fresh look at the photosynthetic process

During "normal" photosynthesis, this vital gas is produced as a "by-product". In normal mode, photosynthetic "factories" are needed to bind CO 2 and produce carbohydrates, which subsequently act as an energy source in many intracellular processes. The light energy in these "factories" goes to the decomposition of water molecules, during which the electrons necessary for fixing carbon dioxide and carbohydrates are released. This decomposition also releases oxygen O 2 .

In the newly discovered process, only a small part of the electrons released during the decomposition of water is used to assimilate carbon dioxide. The lion's share of them during the reverse process goes to the formation of water molecules from "freshly released" oxygen. At the same time, the energy converted during the newly discovered photosynthetic process is not stored in the form of carbohydrates, but directly goes to vital intracellular energy consumers. However, the detailed mechanism of this process remains a mystery.

From the outside, it may seem that such a modification of the photosynthetic process is a waste of time and energy from the Sun. It is hard to believe that in living nature, where over billions of years of evolutionary trial and error, every little thing turned out to be extremely efficient, there can be a process with such a low efficiency.

Nevertheless, this option allows you to protect the complex and fragile apparatus of photosynthesis from excessive exposure to sunlight.

The fact is that the photosynthetic process in bacteria cannot simply be stopped in the absence of the necessary ingredients in the environment. As long as microorganisms are exposed to solar radiation, they are forced to convert the energy of light into the energy of chemical bonds. In the absence of the necessary components, photosynthesis can lead to the formation of free radicals that are detrimental to the entire cell, and therefore cyanobacteria simply cannot do without a backup option for converting photon energy from water to water.

This effect of reduced conversion of CO 2 to carbohydrates and reduced release of molecular oxygen has already been observed in a series of recent studies in the natural conditions of the Atlantic and Pacific Oceans. As it turned out, reduced content of nutrients and iron ions are observed in almost half of their water areas. Hence,

Roughly half of the energy of sunlight coming to the inhabitants of these waters is converted to bypass the usual mechanism of absorption of carbon dioxide and release of oxygen.

This means that the contribution of marine autotrophs to the process of CO2 uptake was previously substantially overestimated.

As Joe Bury, member of the Carnegie Institution's Department of World Ecology, the new discovery will fundamentally change our understanding of how solar energy is processed in the cells of marine microorganisms. According to him, scientists have yet to discover the mechanism of the new process, but even now its existence will force us to take a different look at modern estimates of the scale of photosynthetic absorption of CO 2 in world waters.

Charles

Why do the oceans have "low productivity" in terms of photosynthesis?

80% of the world's photosynthesis takes place in the ocean. Despite this, the oceans also have low productivity - they cover 75% of the earth's surface, but from the annual 170 billion tons of dry weight recorded through photosynthesis, they provide only 55 billion tons. Do not these two facts, which I encountered separately, contradict? If the oceans fix 80% of the total C O X 2 "role="presentation" style="position: relative;"> CO X C O X 2 "role="presentation" style="position: relative;"> C O X 2 "role="presentation" style="position: relative;"> 2 C O X 2 "role="presentation" style="position: relative;"> C O X 2 "role="presentation" style="position: relative;">C C O X 2 "role="presentation" style="position: relative;">O C O X 2 " role="presentation" style="position: relative;">X C O X 2 "role="presentation" style="position: relative;">2 fixed by photosynthesis on earth and releases 80% of the total O X 2 "role="presentation" style="position: relative;"> O X O X 2 "role="presentation" style="position: relative;"> O X 2 "role="presentation" style="position: relative;"> 2 O X 2 "role="presentation" style="position: relative;"> O X 2 "role="presentation" style="position: relative;">O O X 2 " role="presentation" style="position: relative;">x O X 2 "role="presentation" style="position: relative;">2 Released by photosynthesis on Earth, they must also have been 80% of the dry weight. Is there a way to reconcile these facts? In any case, if 80% of photosynthesis takes place in the oceans, it hardly seems low productivity - then why are the oceans said to have low primary productivity (multiple reasons are also given for this - that light is not available at all depths in the oceans, etc.)? More photosynthesis should mean more productivity!

C_Z_

It would be helpful if you point out where you found these two statistics (80% of the world's productivity is in the ocean and the oceans produce 55/170 million tons of dry weight)

Answers

chocoly

First, we must know what are the most important criteria for photosynthesis; they are: light, CO2, water, nutrients. docenti.unicam.it/tmp/2619.ppt Second, the productivity you are talking about should be called "primary productivity" and is calculated by dividing the amount of carbon converted per unit area (m2) by the time. ww2.unime.it/snchimambiente/PrPriFattMag.doc

Thus, due to the fact that the oceans cover a large area of ​​the world, marine microorganisms can convert a large amount of inorganic carbon into organic (the principle of photosynthesis). The big problem in the oceans is the availability of nutrients; they tend to deposit or react with water or other chemicals, even though marine photosynthetic organisms are mostly found on the surface, where of course light is present. This reduces as a consequence the potential for photosynthetic productivity of the oceans.

WYSIWYG ♦

M Gradwell

If the oceans fix 80% of the total CO2CO2 fixed from land photosynthesis and release 80% of the total O2O2 released from land photosynthesis, they should also account for 80% of the dry weight produced.

First, what is meant by "O 2 released"? Does this mean that "O 2 is released from the oceans into the atmosphere, where it contributes to the growth of surpluses"? This cannot be, since the amount of O 2 in the atmosphere is fairly constant, and there is evidence that it is much lower than during Jurassic times. In general, global O 2 sinks should balance O 2 sources, or if something should slightly exceed them, causing current atmospheric CO2 levels to gradually increase at the expense of O 2 levels.

Thus, by "released" we mean "released during photosynthesis at the time of its action."

The oceans fix 80% of the total photosynthesis-bound CO2, yes, but they also break it down at the same rate. For every algae cell that is photosynthetic, there is one that is dead or dying and consumed by bacteria (which consume O2), or it itself consumes oxygen to maintain its metabolic processes during the night. Thus, the net amount of O 2 emitted by the oceans is close to zero.

Now we have to ask what we mean by "performance" in this context. If a CO 2 molecule is fixed due to algae activity, but then almost immediately becomes unfixed again, is this considered "performance"? But blink and you'll miss it! Even if you don't blink, it's unlikely to be measurable. The dry weight of the algae at the end of the process is the same as at the beginning. so if we define "productivity" as "increase in dry weight of algae", then productivity will be zero.

For algae photosynthesis to have a sustained effect on global CO 2 or O 2 levels, the fixed CO 2 must be incorporated into something less fast than algae. Something like cod or hake, which as a bonus can be collected and put on the tables. "Productivity" usually refers to the ability of the oceans to replenish these things after the harvest, and it's really small compared to the land's ability to produce repeat crops.

It would be a different story if we viewed algae as potentially mass-harvesting, so that their ability to grow like wildfire in the presence of fertilizer runoff from the ground was seen as "productivity" rather than a profound inconvenience. But it's not.

In other words, we tend to define "productivity" in terms of what is beneficial to us as a species, and algae is generally useless.

Oceans and seas occupy 71% (more than 360 million km2) of the Earth's surface. They contain about 1370 million km3 of water. Five huge oceans - Pacific, Atlantic, Indian, Arctic and Southern - are connected to each other through the open sea. In some parts of the Arctic and Southern Oceans, a permanently frozen continental shelf has formed, stretching from the coast (shelf ice). In slightly warmer areas, the sea freezes only in winter, forming pack ice (large floating ice fields up to 2 m thick). Some marine animals use the wind to travel across the sea. The physalia ("Portuguese boat") has a gas-filled bladder that helps to catch the wind. Yantina releases air bubbles that serve as her float raft.

The average depth of water in the oceans is 4000 m, but in some ocean basins it can reach 11 thousand m. Under the influence of wind, waves, tides and currents, the water of the oceans is in constant motion. Waves raised by the wind do not affect deep water masses. This is done by the tides, which move water at intervals corresponding to the phases of the moon. Currents carry water between oceans. As surface currents move, they slowly rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

ocean floor:

Most of the ocean floor is a flat plain, but in some places mountains rise thousands of meters above it. Sometimes they rise above the surface of the water in the form of islands. Many of these islands are active or extinct volcanoes. Mountain ranges stretch across the central part of the bottom of a series of oceans. They are constantly growing due to the outpouring of volcanic lava. Each new flow that brings rock to the surface of underwater ridges forms the topography of the ocean floor.

The ocean floor is mostly covered with sand or silt - rivers bring them. In some places, hot springs flow there, from which sulfur and other minerals precipitate. The remains of microscopic plants and animals sink from the surface of the ocean to the bottom, forming a layer of tiny particles (organic sediment). Under the pressure of overlying water and new sedimentary layers, loose sediment slowly turns into rock.

Ocean zones:

In depth, the ocean can be divided into three zones. In the sunny surface waters above - the so-called zone of photosynthesis - most of the ocean fish swim, as well as plankton (a community of billions of microscopic creatures that live in the water column). Beneath the photosynthesis zone lie the more dimly lit twilight zone and the deep cold waters of the gloom zone. In the lower zones, there are fewer life forms - mainly carnivorous (predatory) fish live there.

In most of the ocean water, the temperature is approximately the same - about 4 ° C. When a person is immersed in depth, the pressure of water on him from above constantly increases, making it difficult to move quickly. At great depths, in addition, the temperature drops to 2 °C. There is less and less light, until finally, at a depth of 1000 m, complete darkness reigns.

Surface life:

Plant and animal plankton in the zone of photosynthesis is food for small animals, such as crustaceans, shrimps, as well as juvenile starfish, crabs and other marine life. Away from protected coastal waters, wildlife is less diverse, but there are many fish and large mammals - for example, whales, dolphins, porpoises. Some of them (baleen whales, giant sharks) feed by filtering the water and swallowing the plankton contained in it. Others (white sharks, barracudas) prey on other fish.

Life in the depths of the sea:

In the cold, dark waters of the ocean depths, hunting animals are able to detect the silhouettes of their victims in the dimmest light, barely penetrating from above. Here, many fish have silvery scales on their sides: they reflect any light and mask the shape of their owners. In some fish, flat on the sides, the silhouette is very narrow, barely noticeable. Many fish have huge mouths and can eat prey larger than themselves. Howliods and Hatchetfish swim with their large mouths open, grabbing whatever they can along the way.

Life in the ocean is represented by a wide variety of organisms - from microscopic single-celled algae and tiny animals to whales exceeding 30 m in length and larger than any animal that has ever lived on land, including the largest dinosaurs. Living organisms inhabit the ocean from the surface to the greatest depths. But of plant organisms, only bacteria and some lower fungi are found everywhere in the ocean. The remaining plant organisms inhabit only the upper illuminated layer of the ocean (mainly to a depth of about 50-100 m), where photosynthesis can take place. Photosynthetic plants create primary production, due to which the rest of the population of the ocean exists.

About 10 thousand species of plants live in the World Ocean. The phytoplankton is dominated by diatoms, peridynes, and coccolithophores from flagellates. Bottom plants include mainly diatoms, green, brown and red algae, as well as several species of herbaceous flowering plants (for example, zoster).

The fauna of the ocean is even more diverse. Representatives of almost all classes of modern free-living animals live in the ocean, and many classes are known only in the ocean. Some of them, such as the lobe-finned coelacanth fish, are living fossils whose ancestors flourished here more than 300 million years ago; others have appeared more recently. The fauna includes more than 160 thousand species: about 15 thousand protozoa (mainly radiolarians, foraminifers, ciliates), 5 thousand sponges, about 9 thousand coelenterates, more than 7 thousand various worms, 80 thousand mollusks, more than 20 thousand crustaceans, 6 thousand echinoderms and less numerous representatives of a number of other groups of invertebrates (bryozoans, brachiopods, pogonophores, tunicates and some others), about 16 thousand fish. Of the vertebrates in the ocean, in addition to fish, turtles and snakes (about 50 species) and more than 100 species of mammals, mainly cetaceans and pinnipeds, live. The life of some birds (penguins, albatrosses, gulls, etc. - about 240 species) is constantly connected with the ocean.

The greatest species diversity of animals is characteristic of tropical regions. The benthic fauna is especially diverse on shallow coral reefs. As depth increases, the diversity of life in the ocean decreases. At the greatest depths (more than 9000-10000 m) inhabited only by bacteria and several dozen species of invertebrates.

The composition of living organisms includes at least 60 chemical elements, the main of which (biogenic elements) are C, O, H, N, S, P, K, Fe, Ca and some others. Living organisms have adapted to life under extreme conditions. Bacteria are found even in ocean hydrotherms at T = 200-250 o C. In the deepest depressions, marine organisms have adapted to live under enormous pressures.

However, the inhabitants of the land were far ahead in terms of species diversity of the inhabitants of the ocean, and primarily due to insects, birds and mammals. Generally the number of species of organisms on land is at least an order of magnitude greater than in the ocean: one to two million species on land versus several hundred thousand species in the ocean. This is due to the wide variety of habitats and ecological conditions on land. But at the same time in the sea it is noted a much greater variety of life forms of plants and animals. The two main groups of marine plants - brown and red algae - do not occur at all in fresh waters. Exclusively marine are echinoderms, chaetognaths and chaetognaths, as well as lower chordates. Mussels and oysters live in huge numbers in the ocean, which forage for their food by filtering organic particles from the water, and many other marine organisms feed on the detritus of the seabed. For every species of land worm, there are hundreds of species of marine worms that feed on bottom sediments.

Marine organisms living in different environmental conditions, feeding in different ways and with different habits, can lead a wide variety of lifestyles. Individuals of some species live only in one place and behave the same throughout their lives. This is typical for most phytoplankton species. Many species of marine animals systematically change their lifestyle throughout their life cycle. They go through the larval stage, and turning into adults, they switch to a nekton lifestyle or lead a lifestyle characteristic of benthic organisms. Other species are sessile or may not go through the larval stage at all. In addition, adults of many species from time to time lead a different lifestyle. For example, lobsters can either crawl along the seabed or swim above it for short distances. Many crabs leave their safe burrows for short foraging excursions, during which they crawl or swim. Adults of most fish species belong to purely nektonic organisms, but among them there are many species that live near the bottom. For example, fish such as cod or flounder swim near the bottom or lie on it most of the time. These fish are called bottom fish, although they feed only on the surface of bottom sediments.

With all the diversity of marine organisms, all of them are characterized by growth and reproduction as integral properties of living beings. In the course of them, all parts of a living organism are updated, modified or developed. To maintain this activity, chemical compounds must be synthesized, that is, recreated from smaller and simpler components. Thus, biochemical synthesis is the most essential sign of life.

Biochemical synthesis is carried out through a number of different processes. Since work is being done, each process needs a source of energy. This is primarily the process of photosynthesis, during which almost all organic compounds present in living beings are created due to the energy of sunlight.

The process of photosynthesis can be described by the following simplified equation:

CO 2 + H 2 O + Kinetic energy of sunlight \u003d Sugar + Oxygen, or Carbon dioxide + Water + Sunlight \u003d Sugar + Oxygen

To understand the basics of the existence of life in the sea, it is necessary to know the following four features of photosynthesis:

only some marine organisms are capable of photosynthesis; they include plants (algae, grasses, diatoms, coccolithophores) and some flagellates;

raw materials for photosynthesis are simple inorganic compounds (water and carbon dioxide);

photosynthesis produces oxygen;

energy in chemical form is stored in the sugar molecule.

The potential energy stored in sugar molecules is used by both plants and animals to perform the most important life functions.

Thus, solar energy, initially absorbed by a green plant and stored in sugar molecules, can subsequently be used by the plant itself or by some animal that consumes this sugar molecule as part of food. Consequently, all life on the planet, including life in the ocean, depends on the flow of solar energy, which is retained by the biosphere through the photosynthetic activity of green plants and is transported in chemical form as part of food from one organism to another.

The main building blocks of living matter are carbon, hydrogen and oxygen atoms. Iron, copper, cobalt and many other elements are needed in small quantities. Non-living, forming parts of marine organisms, consist of compounds of silicon, calcium, strontium and phosphorus. Thus, the maintenance of life in the ocean is associated with the continuous consumption of matter. Plants receive the necessary substances directly from sea water, and animal organisms, in addition, receive part of the substances in the composition of food.

Depending on the energy sources used, marine organisms are divided into two main types: autotrophs (autotrophs) and heterotrophs (heterotrophs).

autotrophs, or "self-creating" organisms create organic compounds from the inorganic components of sea water and carry out photosynthesis using the energy of sunlight. However, autotrophic organisms with other modes of nutrition are also known. For example, microorganisms synthesizing hydrogen sulfide (H 2 S) and carbon dioxide (CO 2) draw energy not from the flux of solar radiation, but from some compounds, for example, hydrogen sulfide. Instead of hydrogen sulfide, nitrogen (N 2) and sulfate (SO 4) can be used for the same purpose. This type of autotroph is called chemo m rofam u .

Heterotrophs ("those who eat others") depend on the organisms they use as food. To live, they must consume either living or dead tissues of other organisms. The organic matter of their food provides the supply of all the chemical energy necessary for independent biochemical synthesis, and the substances necessary for life.

Each marine organism interacts with other organisms and with the water itself, its physical and chemical characteristics. This system of interactions forms marine ecosystem . The most important feature of the marine ecosystem is the transfer of energy and matter; in fact, it is a kind of "machine" for the production of organic matter.

Solar energy is absorbed by plants and transferred from them to animals and bacteria in the form of potential energy. main food chain . These consumer groups exchange carbon dioxide, mineral nutrients and oxygen with plants. Thus, the flow of organic substances is closed and conservative; between the living components of the system, the same substances circulate in the forward and backward directions, directly entering this system or replenished through the ocean. Ultimately, all incoming energy is dissipated in the form of heat as a result of mechanical and chemical processes occurring in the biosphere.

Table 9 describes the components of the ecosystem; it lists the most basic nutrients used by plants, and the biological component of an ecosystem includes both living and dead matter. The latter gradually decomposes into biogenic particles due to bacterial decomposition.

biogenic remains make up about half of the total substance of the marine part of the biosphere. Suspended in water, buried in bottom sediments and sticking to all protruding surfaces, they contain a huge supply of food. Some pelagic animals feed exclusively on dead organic matter, and for many other inhabitants it sometimes forms a significant part of the diet in addition to living plankton. However, the main consumers of organic detritus are benthic organisms.

The number of organisms living in the sea varies in space and time. The blue tropical waters of the open parts of the oceans contain significantly less plankton and nekton than the greenish waters of the coasts. The total mass of all living marine individuals (microorganisms, plants and animals) per unit area or volume of their habitat is biomass. It is usually expressed in terms of wet or dry matter (g/m 2 , kg/ha, g/m 3). Plant biomass is called phytomass, animal biomass is called zoomass.

The main role in the processes of new formation of organic matter in water bodies belongs to chlorophyll-containing organisms, mainly phytoplankton. primary production - the result of the vital activity of phytoplankton - characterizes the result of the process of photosynthesis, during which organic matter is synthesized from the mineral components of the environment. The plants that make it are called n primary producers . In the open sea, they create almost all organic matter.

Table 9

Marine Ecosystem Components

Thus, primary production is the mass of newly formed organic matter over a certain period of time. A measure of primary production is the rate of new formation of organic matter.

There are gross and net primary production. Gross primary production refers to the total amount of organic matter formed during photosynthesis. It is the gross primary production in relation to phytoplankton that is a measure of photosynthesis, since it gives an idea of ​​the amount of matter and energy that are used in further transformations of matter and energy in the sea. Net primary production refers to that part of the newly formed organic matter that remains after being spent on metabolism and that remains directly available for use by other organisms in the water as food.

The relationship between different organisms associated with food consumption is called trophic . They are important concepts in ocean biology.

The first trophic level is represented by phytoplankton. The second trophic level is formed by herbivorous zooplankton. The total biomass formed per unit of time at this level is secondary products of the ecosystem. The third trophic level is represented by carnivores, or predators of the first rank, and omnivores. The total production at this level is called tertiary. The fourth trophic level is formed by predators of the second rank, which feed on organisms of lower trophic levels. Finally, at the fifth trophic level there are predators of the third rank.

The concept of trophic levels makes it possible to judge the efficiency of an ecosystem. Energy either from the Sun or as part of food is supplied to each trophic level. A significant proportion of the energy that has entered one or another level is dissipated on it and cannot be transferred to higher levels. These losses include all the physical and chemical work done by living organisms to sustain themselves. In addition, animals of higher trophic levels consume only a certain proportion of the products formed at lower levels; some plants and animals die for natural reasons. As a result, the amount of energy that is extracted from any trophic level by organisms at a higher level of the food web is less than the amount of energy that has entered the lower level. The ratio of the corresponding amounts of energy is called environmental efficiency trophic level and is usually 0.1-0.2. Eco-efficiency values trophic levels are used to calculate biological production.

Rice. 41 shows in a simplified form the spatial organization of energy and matter flows in the real ocean. In the open ocean, the euphotic zone, where photosynthesis occurs, and the deep regions, where photosynthesis is absent, are separated by a considerable distance. It means that the transfer of chemical energy to the deep layers of water leads to a constant and significant outflow of biogens (nutrients) from surface waters.

Rice. 41. The main directions of the exchange of energy and matter in the ocean

Thus, the processes of energy and matter exchange in the ocean together form an ecological pump that pumps out the main nutrients from the surface layers. If the opposite processes did not act to make up for this loss of matter, then the surface waters of the ocean would be deprived of all nutrients and life would dry up. This catastrophe does not occur only due, first of all, to upwelling, which brings deep waters to the surface at an average speed of about 300 m/year. The rise of deep waters saturated with biogenic elements is especially intense near the western coasts of the continents, near the equator and at high latitudes, where the seasonal thermocline collapses and a significant water column is covered by convective mixing.

Since the total production of a marine ecosystem is determined by the value of production at the first trophic level, it is important to know what factors influence it. These factors include:

illumination of the surface layer ocean waters;

water temperature;

supply of nutrients to the surface;

the rate of consumption (eating) of plant organisms.

Illumination of the surface layer of water determines the intensity of the photosynthesis process, therefore, the amount of light energy entering a particular area of ​​the ocean limits the amount of organic production. In my turn the intensity of solar radiation is determined by geographical and meteorological factors, especially height of the Sun above the horizon and cloud cover. In water, light intensity decreases rapidly with depth. As a result, the primary production zone is limited to the upper few tens of meters. In coastal waters, which usually contain much more suspended solids than in the waters of the open ocean, the penetration of light is even more difficult.

Water temperature also affects the value of primary production. At the same light intensity, the maximum rate of photosynthesis is achieved by each species of algae only in a certain temperature range. Increasing or decreasing the temperature relative to this optimal interval leads to a decrease in the production of photosynthesis. However, in most of the ocean, for many species of phytoplankton, the water temperature is below this optimum. Therefore, seasonal warming of water causes an increase in the rate of photosynthesis. The maximum rate of photosynthesis in various species of algae is observed at about 20°C.

For the existence of marine plants are necessary nutrients - macro- and microbiogenic elements. Macrobiogens - nitrogen, phosphorus, silicon, magnesium, calcium and potassium are needed in relatively large quantities. Microbiogens, that is, elements required in minimal amounts, include iron, manganese, copper, zinc, boron, sodium, molybdenum, chlorine, and vanadium.

Nitrogen, phosphorus and silicon are contained in water in such small quantities that they do not satisfy the needs of plants and limit the intensity of photosynthesis.

Nitrogen and phosphorus are needed for the construction of cell matter and, in addition, phosphorus takes part in energy processes. Nitrogen is needed more than phosphorus, since in plants the ratio "nitrogen: phosphorus" is approximately 16: 1. Usually this is the ratio of the concentrations of these elements in sea water. However, in coastal waters, nitrogen recovery processes (that is, the processes by which nitrogen is returned to the water in a form suitable for plant consumption) are slower than phosphorus recovery processes. Therefore, in many coastal areas, the content of nitrogen decreases relative to the content of phosphorus, and it acts as an element that limits the intensity of photosynthesis.

Silicon is consumed in large quantities by two groups of phytoplankton organisms - diatoms and dinoflagellates (flagellates), which build their skeletons from it. Sometimes they extract silicon from surface waters so quickly that the resulting lack of silicon begins to limit their development. As a result, after the seasonal outbreak of silicon-consuming phytoplankton, the rapid development of "non-siliceous" forms of phytoplankton begins.

Consumption (eating) of phytoplankton zooplankton immediately affects the value of primary production, because each plant eaten will no longer grow and reproduce. Consequently, the intensity of grazing is one of the factors affecting the rate of creation of primary products. In an equilibrium situation, the intensity of grazing should be such that the phytoplankton biomass remains at a constant level. With an increase in primary production, an increase in zooplankton population or grazing intensity could theoretically bring this system back into balance. However, it takes time for zooplankton to multiply. Therefore, even with the constancy of other factors, a steady state is never achieved, and the number of zoo- and phytoplankton organisms fluctuates around a certain level of equilibrium.

Biological productivity of sea waters changes markedly in space. Areas of high productivity include continental shelves and open ocean waters, where upwelling results in the enrichment of surface waters with nutrients. The high productivity of shelf waters is also determined by the fact that relatively shallow shelf waters are warmer and better illuminated. Nutrient-rich river waters come here first of all. In addition, the supply of biogenic elements is replenished by the decomposition of organic matter on the seabed. In the open ocean, the area of ​​​​areas with high productivity is insignificant, because here planetary scale subtropical anticyclonic gyres are traced, which are characterized by the processes of subsidence of surface waters.

The water areas of the open ocean with the greatest productivity are confined to high latitudes; their northern and southern border usually coincides with latitude 50 0 in both hemispheres. Autumn-winter cooling leads here to powerful convective movements and the removal of biogenic elements from deep layers to the surface. However, with further advancement to high latitudes, productivity will begin to decrease due to the increasing predominance of low temperatures, deteriorating illumination due to the low height of the Sun above the horizon and ice cover.

Areas of intense coastal upwelling are highly productive in the zone of boundary currents in the eastern parts of the oceans off the coast of Peru, Oregon, Senegal, and southwestern Africa.

In all regions of the ocean, there is a seasonal variation in the value of primary production. This is due to the biological responses of phytoplankton organisms to seasonal changes in the physical conditions of their habitat, especially illumination, wind strength and water temperature. The greatest seasonal contrasts are typical for the seas of the temperate zone. Due to the thermal inertia of the ocean, surface water temperature changes lag behind air temperature changes, and therefore, in the northern hemisphere, the maximum water temperature is observed in August, and the minimum in February. By the end of winter, as a result of low water temperatures and a decrease in the arrival of solar radiation penetrating into the water, the number of diatoms and dinoflagellates is greatly reduced. Meanwhile, due to significant cooling and winter storms, surface waters are mixed to a great depth by convection. The rise of deep, nutrient-rich waters leads to an increase in their content in the surface layer. With the warming of waters and an increase in illumination, optimal conditions are created for the development of diatoms and an outbreak of the number of phytoplankton organisms is noted.

At the beginning of summer, despite optimal temperature conditions and illumination, a number of factors lead to a decrease in the number of diatoms. First, their biomass is reduced due to grazing by zooplankton. Secondly, due to the heating of surface waters, a strong stratification is created, which suppresses vertical mixing and, consequently, the removal of nutrient-rich deep waters to the surface. Optimal conditions at this time are created for the development of dinoflagellates and other forms of phytoplankton that do not need silicon to build a skeleton. In autumn, when the illumination is still sufficient for photosynthesis, the thermocline is destroyed due to the cooling of surface waters, and conditions for convective mixing are created. Surface waters begin to be replenished with nutrients from deep layers of water, and their productivity increases, especially in connection with the development of diatoms. With a further decrease in temperature and illumination, the abundance of phytoplankton organisms of all species decreases to a low winter level. At the same time, many species of organisms fall into suspended animation, acting as a "seed" for a future spring outbreak.

At low latitudes, changes in productivity are relatively small and reflect mainly changes in vertical circulation. Surface waters are always very warm, and their constant feature is a pronounced thermocline. As a result, the removal of deep, nutrient-rich waters from under the thermocline to the surface layer is impossible. Therefore, despite favorable other conditions, far from upwelling areas in tropical seas, low productivity is noted.