To what depth in the World Ocean does the photosynthetic zone extend? Efficiency of photosynthesis in terrestrial and marine ecosystems. Cyanobacteria are able to “short-circuit” 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 occurs in the ocean. Despite this, the oceans also have low productivity - they cover 75% of the earth's surface, but of the annual 170 billion tons of dry weight recorded through photosynthesis, they provide only 55 billion tons. Aren't these two facts that I encountered separately contradictory? If the oceans fix 80% of the total C O X 2 " role="presentation" style="position: relative;"> C O 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 accounted for 80% of the dry weight. Is there a way to reconcile these facts? In any case, if 80% of photosynthesis occurs in the oceans, it hardly seems low productivity - then why are the oceans said to have low primary productivity (many reasons are also given for this - that light is not available at all depths in the oceans, etc.)? More photosynthesis must mean more productivity!

C_Z_

It would be helpful if you could point out where you found these two statistics (80% of the world's productivity comes from 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; these are: light, CO 2, water, nutrients. docenti.unicam.it/tmp/2619.ppt Secondly, 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 time. www2.unime.it/snchimambiente/PrPriFattMag.doc

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

WYSIWYG♦

MTGradwell

If the oceans fix 80% of the total CO2CO2 fixed by photosynthesis on earth, and release 80% of the total O2O2 fixed by photosynthesis on earth, they must also account for 80% of the resulting dry weight.

Firstly, 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 excess growth"? This cannot be the case since the amount of O2 in the atmosphere is fairly constant and there is evidence that it is significantly lower than in Jurassic times. In general, global O2 sinks should balance O2 sources or, if anything, slightly exceed them, causing current atmospheric CO2 levels to gradually increase at the expense of O2 levels.

So by "released" we mean "released by the process of photosynthesis at the moment of its action."

The oceans fix 80% of the total CO 2 fixed through photosynthesis, 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 is consumed by bacteria (which consume O2), or it itself consumes oxygen to maintain its metabolic processes at night. Thus, the net amount of O 2 released by the oceans is close to zero.

We must now ask what we mean by "performance" in this context. If a CO2 molecule becomes fixed due to algae activity, but then almost immediately becomes unfixed again, is that considered "productivity"? But blink and you'll miss it! Even if you don't blink, it's unlikely to be measurable. The dry weight of algae at the end of the process is the same as at the beginning. therefore, if we define "productivity" as "increase in algae dry mass", then the productivity would be zero.

For algae photosynthesis to have a sustainable effect on global CO 2 or O 2 levels, the fixed CO 2 must be incorporated into something less rapid than algae. Something like cod or hake, which can be collected and placed on tables as a bonus. "Productivity" usually refers to the ability of the oceans to replenish these things after harvest, and this is really small compared to the ability of the earth to produce repeat harvests.

It would be a different story if we viewed algae as potentially suitable for mass harvesting, so that its ability to grow like wildfire in the presence of fertilizer runoff from the land was seen as "productivity" rather than a profound nuisance. But that's not true.

In other words, we tend to define "productivity" in terms of what's good for us as a species, and algae tends to be not.

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

Most likely, the same process at one time marked the beginning of 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 complex organisms. And until now, according to many scientists, only photosynthesis is able to contain the rapid 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. Light energy in these “factories” is used to decompose water molecules, during which the electrons necessary for fixing carbon dioxide and carbohydrates are released. During this decomposition, oxygen O 2 is also released.

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. In this case, the energy converted during the newly discovered photosynthetic process is not stored in the form of carbohydrates, but is directly supplied to vital intracellular energy consumers. However, the detailed mechanism of this process still 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 detail has turned out to be extremely efficient, a process with such a low efficiency can exist.

Nevertheless, this option allows you to protect the complex and fragile photosynthetic apparatus 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 light energy into the energy of chemical bonds. In the absence of the necessary components, photosynthesis can lead to the formation of free radicals that are destructive 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 a reduced level of conversion of CO 2 into carbohydrates and a 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, low levels of nutrients and iron ions are observed in almost half of their water areas. Hence,

About half of the energy from sunlight reaching the inhabitants of these waters is converted by bypassing the usual mechanism of absorbing carbon dioxide and releasing oxygen.

This means that the contribution of marine autotrophs to the process of CO 2 absorption was previously significantly overestimated.

As one of the specialists in the Department of Global Ecology at the Carnegie Institution, Joe Bury, the new discovery will significantly change our understanding of the processes of processing solar energy in the cells of marine microorganisms. According to him, scientists have yet to uncover the mechanism of the new process, but already its existence will force us to take a different look at modern estimates of the scale of photosynthetic absorption of CO 2 in the world's waters.

Charles

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

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

C_Z_

It would be helpful if you could point out where you found these two statistics (80% of the world's productivity comes from 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; these are: light, CO 2, water, nutrients. docenti.unicam.it/tmp/2619.ppt Secondly, 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 time. www2.unime.it/snchimambiente/PrPriFattMag.doc

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

WYSIWYG♦

MTGradwell

If the oceans fix 80% of the total CO2CO2 fixed by photosynthesis on earth, and release 80% of the total O2O2 fixed by photosynthesis on earth, they must also account for 80% of the resulting dry weight.

Firstly, 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 excess growth"? This cannot be the case since the amount of O2 in the atmosphere is fairly constant and there is evidence that it is significantly lower than in Jurassic times. In general, global O2 sinks should balance O2 sources or, if anything, slightly exceed them, causing current atmospheric CO2 levels to gradually increase at the expense of O2 levels.

So by "released" we mean "released by the process of photosynthesis at the moment of its action."

The oceans fix 80% of the total CO 2 fixed through photosynthesis, 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 is consumed by bacteria (which consume O2), or it itself consumes oxygen to maintain its metabolic processes at night. Thus, the net amount of O 2 released by the oceans is close to zero.

We must now ask what we mean by "performance" in this context. If a CO2 molecule becomes fixed due to algae activity, but then almost immediately becomes unfixed again, is that considered "productivity"? But blink and you'll miss it! Even if you don't blink, it's unlikely to be measurable. The dry weight of algae at the end of the process is the same as at the beginning. therefore, if we define "productivity" as "increase in algae dry mass", then the productivity would be zero.

For algae photosynthesis to have a sustainable effect on global CO 2 or O 2 levels, the fixed CO 2 must be incorporated into something less rapid than algae. Something like cod or hake, which can be collected and placed on tables as a bonus. "Productivity" usually refers to the ability of the oceans to replenish these things after harvest, and this is really small compared to the ability of the earth to produce repeat harvests.

It would be a different story if we viewed algae as potentially suitable for mass harvesting, so that its ability to grow like wildfire in the presence of fertilizer runoff from the land was seen as "productivity" rather than a profound nuisance. But that's not true.

In other words, we tend to define "productivity" in terms of what's good for us as a species, and algae tends to be not.

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, extending 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. Physalia ("Portuguese man-of-war") has a gas-filled bladder that helps 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 depressions it can reach 11 thousand m. Under the influence of wind, waves, tides and currents, ocean water 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. Surface currents, moving, slowly rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.

Ocean bottom:

Most of the ocean floor is flat, 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 number of oceans. They are constantly growing due to the outpouring of volcanic lava. Each new flow that carries rock to the surface of underwater ridges forms the topography of the ocean floor.

The ocean floor is mostly covered with sand or silt - they are brought by rivers. In some places there are hot springs, from which sulfur and other minerals are deposited. 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 pressure from overlying water and new sediment layers, the loose sediment slowly turns into rock.

Oceanic zones:

In depth, the ocean can be divided into three zones. In the sunny surface waters above - the so-called photosynthetic zone - most 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 dimly lit twilight zone and the deep, cold waters of the gloom zone. Fewer life forms are found in the lower zones - mainly carnivorous (predatory) fish live there.

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

Life at the surface:

Plant and animal plankton in the photosynthetic zone provide food for small animals, such as crustaceans, shrimp, as well as juvenile starfish, crabs and other marine life. Away from the sheltered coastal waters, wildlife is less diverse, but there are many fish and large mammals such as whales, dolphins, and 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 camouflage the shape of their owners. Some fish, flat on the sides, have a very narrow silhouette, barely noticeable. Many fish have huge mouths and can eat prey that is larger than them. Howliods and hatchetfish swim with their large mouths open, grabbing whatever they can along the way.

Life in the ocean ranges from microscopic single-celled algae and tiny animals to whales that are over 100 feet long 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 among 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), in which photosynthesis can take place. Photosynthetic plants create primary production, due to which the rest of the ocean population exists.

About 10 thousand species of plants live in the World Ocean. Phytoplankton is dominated by diatoms, peridinians and flagellated coccolithophores. Benthic plants include mainly diatoms, green algae, brown algae and red algae, as well as several species of herbaceous flowering plants (eg zostera).

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, such as the lobe-finned fish coelacanth, 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, foraminifera, 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, pogonophora, tunicates and some others), about 16 thousand fish. Of the vertebrate animals in the ocean, in addition to fish, there are turtles and snakes (about 50 species) and more than 100 species of mammals, mainly cetaceans and pinnipeds. 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. Bottom 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) only bacteria and several dozen species of invertebrate animals live.

Living organisms include 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 at enormous pressures.

However, the inhabitants of the land were far ahead in terms of species diversity of the inhabitants of the ocean, 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 found in the ocean. This is due to the wide variety of habitats and ecological conditions on land. But at the same time, the sea celebrates significantly greater diversity of life forms of plants and animals. The two main groups of marine plants - brown and red algae - are not found at all in fresh waters. Exclusively marine are echinoderms, chaetognaths and chaetognathates, as well as lower chordates. The ocean is home to huge quantities of mussels and oysters, which obtain their food by filtering organic particles from the water, and many other marine organisms feed on detritus of the seabed. For every type of land worm, there are hundreds of species of sea worms that feed on bottom sediments.

Marine organisms living in different environmental conditions, eating differently and with different habits can lead very different lifestyles. Individuals of some species live in only one place and behave the same throughout their lives. This is typical for most species of phytoplankton. Many species of marine animals systematically change their lifestyle throughout their life cycle. They go through the larval stage, and having turned into adults, they switch to a nektonic lifestyle or lead a lifestyle typical of benthic organisms. Other species are sedentary or may not go through the larval stage at all. In addition, adults of many species lead different lifestyles from time to time. For example, lobsters can either crawl along the seabed or swim above it for short distances. Many crabs leave the safety of their burrows for short excursions in search of food, 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 benthic, 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. During them, all parts of a living organism are renewed, modified or developed. To support 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 occurs through a number of different processes. Because work is done, each process requires a source of energy. This is primarily the process of photosynthesis, during which almost all organic compounds present in living beings are created using the energy of sunlight.

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

CO 2 + H 2 O + Kynthetic energy of sunlight = Sugar + Oxygen, or Carbon dioxide + Water + Sunlight = Sugar + Oxygen

To understand the basic existence of life in the sea, you need to know the following four features of photosynthesis:

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

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

Oxygen is produced during photosynthesis;

Energy in chemical form is stored in a sugar molecule.

The potential energy stored in sugar molecules is used by both plants and animals to perform essential 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 due to the photosynthetic activity of green plants and is transferred in chemical form as part of food from one organism to another.

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

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

Autotrophs, or “self-creating” organisms create organic compounds from the inorganic components of seawater and carry out photosynthesis using the energy of sunlight. However, autotrophic organisms with other feeding methods are also known. For example, microorganisms that synthesize hydrogen sulfide (H 2 S) and carbon dioxide (CO 2) draw energy not from the flow 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 (“other-eating”) depend on the organisms they use as food. To live, they must consume either living or dead tissue from other organisms. The organic matter of their food provides all the chemical energy necessary for independent biochemical synthesis and substances necessary for life.

Each marine organism interacts with other organisms and with the water itself and 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 essence, 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; the same substances circulate between the living components of the system in the forward and reverse 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 provides a description of the ecosystem components; 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 breaks down into biogenic particles due to bacterial decomposition.

Biogenic residues constitute approximately 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. But still, 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 oceans contain significantly less plankton and nekton than the greenish waters of the coasts. The total mass of all living marine species (microorganisms, plants and animals) per unit surface or volume of their habitat is biomass. It is usually expressed in the mass of wet or dry matter (g/m2, kg/ha, g/m3). 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 create it are called n primary producers . In the open sea, they create almost all organic matter.

Table 9

Components of the Marine Ecosystem

Thus, primary production represents 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 products. Gross primary production refers to the entire amount of organic matter formed during photosynthesis. It is 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 which remains directly available for use by other organisms in the water as food.

The relationships between different organisms related to food consumption are 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 time at this level is secondary products of the ecosystem. The third trophic level is represented by carnivores, or first-rank predators, and omnivores. The total production at this level is called tertiary. The fourth trophic level is formed by second-rank predators that feed on organisms of lower trophic levels. Finally, at the fifth trophic level there are predators of the third rank.

Understanding trophic levels allows us to judge the effectiveness of an ecosystem. Energy either from the Sun or as part of food is supplied to each trophic level. A significant portion of the energy received at one or another level is dissipated there and cannot be transferred to higher levels. These losses include all the physical and chemical work performed by living organisms to maintain themselves. In addition, animals at higher trophic levels consume only a certain proportion of the production generated at lower levels; Some plants and animals die off due to natural reasons. As a result, the amount of energy that is extracted from a trophic level by organisms at a higher level of the food web is less than the amount of energy supplied to 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 level are used to calculate biological production.

Rice. 41 shows in a simplified form the spatial organization of energy and matter flows in a real ocean. In the open ocean, the euphotic zone, where photosynthesis occurs, and the deep regions, where photosynthesis does not occur, are separated by a considerable distance. It means that The transfer of chemical energy into deep layers of water leads to a constant and significant outflow of nutrients (nutrients) from surface waters.

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

Thus, the processes of exchange of energy and matter in the ocean together form an ecological pump, pumping out basic nutrients from the surface layers. If opposite processes did not operate to compensate for this loss of matter, then the surface waters of the ocean would lose all nutrients and life would dry up. This catastrophe does not occur only due, first of all, to upwelling, which carries deep water to the surface at an average speed of approximately 300 m/year. The rise of deep waters saturated with nutrients is especially intense along the western coasts of continents, near the equator and in high latitudes, where the seasonal thermocline is destroyed and a significant thickness of water is covered by convective mixing.

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

surface layer illumination ocean waters;

water temperature;

supply of nutrients to the surface;

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 ocean area limits the amount of organic production. In your In turn, the intensity of solar radiation is determined by geographical and meteorological factors, especially the height of the Sun above the horizon and cloudiness. 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 typically contain significantly more suspended solids than in open ocean waters, light penetration is even more difficult.

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

For the existence of marine plants it is 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 quantities, 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 plants’ need for them and limit the intensity of photosynthesis.

Nitrogen and phosphorus are needed to build cell matter and, in addition, phosphorus takes part in energy processes. More nitrogen is needed than phosphorus, since in plants the nitrogen: phosphorus ratio is approximately 16: 1. This is usually the ratio of the concentrations of these elements in seawater. However, in coastal waters, nitrogen regeneration processes (that is, processes that return nitrogen to the water in a form suitable for plant consumption) are slower than phosphorus regeneration processes. Therefore, in many coastal areas, the nitrogen content decreases relative to the phosphorus content, and it acts as an element limiting the intensity of photosynthesis.

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

Consumption (grazing) of phytoplankton zooplankton immediately affects the amount of primary production, because each plant eaten will no longer grow and reproduce. Consequently, the intensity of grazing is one of the factors influencing the rate of creation of primary production. In an equilibrium situation, the intensity of grazing should be such that the phytoplankton biomass remains at a constant level. As primary production increases, increases in zooplankton populations or grazing rates could theoretically bring the system back into equilibrium. However, it takes time for zooplankton to reproduce. Therefore, even if other factors are constant, a steady state is never achieved, and the number of zoo- and phytoplankton organisms fluctuates around a certain equilibrium level.

Biological productivity of sea waters changes noticeably in space. Areas of high productivity include continental shelves and open ocean waters, where, as a result of upwelling, surface waters are enriched 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 primarily flow here. In addition, the supply of nutrients 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 planetary-scale subtropical anticyclonic circulations are traced here, which are characterized by processes of subsidence of surface waters.

The open ocean waters with the greatest productivity are confined to high latitudes; their northern and southern boundaries usually coincide with latitude 50 0 in both hemispheres. Autumn-winter cooling here leads to powerful convective movements and the removal of nutrients from deep layers to the surface. However, as we move further into 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 in the zone of boundary currents in the eastern parts of the oceans off the coast of Peru, Oregon, Senegal and southwest Africa are highly productive.

In all areas of the ocean, there is a seasonal variation in the amount of primary production. This is due to the biological responses of phytoplanktonic organisms to seasonal changes in the physical conditions of the habitat, especially light, wind strength and water temperature. The greatest seasonal contrasts are characteristic of the seas of the temperate zone. Due to the thermal inertia of the ocean, changes in surface water temperature lag behind changes in air temperature, 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 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 greater depths by convection. The rise of deep, nutrient-rich waters leads to an increase in their content in the surface layer. With warming waters and increasing light levels, optimal conditions are created for the development of diatoms and an outbreak in the number of phytoplankton organisms is noted.

At the beginning of summer, despite optimal temperature and light conditions, a number of factors lead to a decrease in the number of diatoms. Firstly, their biomass decreases due to grazing by zooplankton. Secondly, due to the heating of surface waters, a strong stratification is created, suppressing vertical mixing and, consequently, the removal of deep waters enriched with nutrients to the surface. Optimal conditions at this time are created for the development of dinoflagellates and other forms of phytoplankton that do not require silicon to build a skeleton. In autumn, when the illumination is still sufficient for photosynthesis, due to the cooling of surface waters, the thermocline is destroyed, creating conditions for convective mixing. Surface waters begin to be replenished with nutrients from deeper layers of water, and their productivity increases, especially due to the development of diatoms. With a further decrease in temperature and light, the number of phytoplankton organisms of all species decreases to low winter levels. At the same time, many species of organisms fall into suspended animation, acting as “seed material” 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 into the surface layer is impossible. Therefore, despite other favorable conditions, low productivity is observed far from upwelling areas in tropical seas.