The ocean accounts for some of the photosynthesis. Why do the oceans have "low productivity" in terms of photosynthesis? Distribution of life in the seas and oceans

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 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 photosynthesis zone is food for small animals, such as crustaceans, shrimp, and juveniles starfish, crabs and others sea ​​creatures. Away from sheltered coastal waters animal world less diverse, but many fish live here and large mammals- for example, whales, dolphins, porpoises. Some of them (baleen whales, giant sharks) feed by filtering water and ingesting plankton contained in it. Others (white sharks, barracudas) prey on other fish.

Life in the depths of the sea:

In cold, dark waters 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.

The biosphere (from the Greek “bios” - life, “sphere” - ball) as a carrier of life arose with the appearance of living beings as a result evolutionary development planets. The biosphere refers to the part of the Earth's shell inhabited by living organisms. The doctrine of the biosphere was created by academician Vladimir Ivanovich Vernadsky (1863-1945). V.I. Vernadsky is the founder of the doctrine of the biosphere and the method of determining the age of the Earth based on the half-life of radioactive elements. He was the first to reveal the enormous role of plants, animals and microorganisms in the movement of chemical elements earth's crust.

The biosphere has certain boundaries. Upper limit The biosphere is located at an altitude of 15-20 km from the Earth's surface. It takes place in the stratosphere. The bulk of living organisms are located in the lower air shell - the troposphere. The lowest part of the troposphere (50-70 m) is the most populated.

The lower boundary of life passes through the lithosphere at a depth of 2-3 km. Life is concentrated mainly in the upper part of the lithosphere - in the soil and on its surface. Water shell planets (hydrosphere) occupies up to 71% of the Earth's surface.

If we compare the size of all geospheres, we can say that the lithosphere has the largest mass, the atmosphere the smallest. The biomass of living beings is small compared to the size of geospheres (0.01%). IN different parts The density of life in the biosphere is not the same. Largest quantity organisms are located at the surface of the lithosphere and hydrosphere. The biomass content also varies by zone. Tropical forests have the maximum density, while Arctic ice and high mountain areas have the lowest density.

Biomass. The organisms that make up the biomass have a tremendous ability to reproduce and spread throughout the planet (see section “Struggle for existence”). Reproduction determines density of life. It depends on the size of the organisms and the area required for life. The density of life creates a struggle among organisms for space, food, air, and water. In progress natural selection and fitness, a large number of organisms with the highest density of life are concentrated in one area.

Land biomass.

On the Earth's land, starting from the poles to the equator, biomass gradually increases. The greatest concentration and diversity of plants occurs in humid tropical forests. The number and diversity of animal species depends on the plant mass and also increases towards the equator. Food chains, intertwined, form a complex network of transfer of chemical elements and energy. There is a fierce struggle between organisms for the possession of space, food, light, and oxygen.

Soil biomass. As a living environment, soil has a number of specific features: high density, small amplitude of temperature fluctuations; it is opaque, poor in oxygen, and contains water in which mineral salts are dissolved.

The inhabitants of the soil represent a unique biocenotic complex. The soil contains a lot of bacteria (up to 500 t/ha), decomposing organic matter of fungi, and green and blue-green algae live in the surface layers, enriching the soil with oxygen through the process of photosynthesis. The thickness of the soil is penetrated by roots higher plants, is rich in protozoa - amoebas, flagellates, ciliates. Even Charles Darwin drew attention to the role of earthworms, which loosen the soil, swallow it and soak it with gastric juice. In addition, ants, ticks, moles, marmots, gophers and other animals live in the soil. All inhabitants of the soil do a lot of soil-forming work and participate in creating soil fertility. Many soil organisms take part in the general cycle of substances occurring in the biosphere.

Biomass of the World Ocean.

The Earth's hydrosphere, or the World Ocean, occupies more than 2/3 of the planet's surface. Water has special properties, important for the life of organisms. Its high heat capacity makes the temperature of oceans and seas more uniform, moderating extreme temperature changes in winter and summer. Physical properties And chemical composition Ocean waters are very constant and create an environment favorable for life. The ocean accounts for about 1/3 of the photosynthesis that occurs on the entire planet.

Suspended in water unicellular algae and the smallest animals form plankton. Plankton is of primary importance in the nutrition of ocean fauna.

In the ocean, in addition to plankton and free-swimming animals, there are many organisms attached to the bottom and crawling along it. The inhabitants of the bottom are called benthos.

There is 1000 times less living biomass in the World Ocean than on land. In all parts of the World Ocean there are microorganisms that decompose organic matter into mineral matter.

The circulation of substances and the transformation of energy in the biosphere. Plant and animal organisms, being in relationship with the inorganic environment, are included in the continuously occurring cycle of substances and energy in nature.

Carbon is found naturally in rocks in the form of limestone and marble. Most carbon is found in the atmosphere as carbon dioxide. Carbon dioxide is absorbed from the air by green plants during photosynthesis. Carbon is included in the cycle due to the activity of bacteria that destroy the dead remains of plants and animals.

When plants and animals decompose, nitrogen is released in the form of ammonia. Nitrophizing bacteria convert ammonia into salts of nitrous and nitric acids, which are absorbed by plants. In addition, some nitrogen-fixing bacteria are capable of assimilating atmospheric nitrogen.

Rocks contain large reserves of phosphorus. When destroyed, these rocks release phosphorus to the ground ecological systems, however, some of the phosphates are drawn into the water cycle and carried out to the sea. Together with dead residues, phosphates sink to the bottom. One part of them is used, and the other is lost in deep sediments. Thus, there is a discrepancy between phosphorus consumption and its return to the cycle.

As a result of the cycle of substances in the biosphere, continuous biogenic migration of elements occurs. Necessary for the life of plants and animals chemical elements pass from the environment into the body. When organisms decompose, these elements return to the environment, from where they again enter the body.

Various organisms, including humans, take part in the biogenic migration of elements.

The role of man in the biosphere. Man is part of the biomass of the biosphere - for a long time was directly dependent on surrounding nature. With the development of the brain, man himself becomes a powerful factor in further evolution on Earth. Mastery of Man various forms energy - mechanical, electrical and atomic - contributed significant change the earth's crust and biogenic migration of atoms. Along with benefits, human intervention in nature often brings harm to it. Human activities often lead to disruption natural patterns. Disruption and change of the biosphere are of serious concern. In this regard, in 1971, UNESCO (United Nations Educational, Scientific and Cultural Organization), which includes the USSR, adopted the International Biological Program (IBP) “Man and the Biosphere”, which studies changes in the biosphere and its resources under human influence.

Article 18 of the USSR Constitution says: “In the interests of present and future generations, the USSR adopts necessary measures for protection and scientifically based, rational use earth and its subsoil, water resources, flora and fauna, to maintain clean air and water, ensure reproduction natural resources and improvements surrounding a person environment."

There are several types of cytological tasks.

1. In the topic “Chemical organization of the cell” they solve problems on constructing the second helix of DNA; determining the percentage of content of each nucleotide, etc., for example, task No. 1. On a section of one DNA chain there are nucleotides: T - C - T-A - G - T - A - A - T. Determine: 1) the structure of the second chain, 2) the percentage of content of each nucleotide in a given segment.

Solution: 1) The structure of the second chain is determined by the principle of complementarity. Answer: A - G - A - T - C - A - T -T - A.

2) There are 18 nucleotides (100%) in two chains of this DNA segment. Answer: A = 7 nucleotides (38.9%) T = 7 - (38.9%); G = 2 - (11.1%) and C = 2 - (11.1%).

II. In the topic “Metabolism and energy conversion in the cell,” they solve problems to determine the primary structure of a protein from the DNA code; gene structure based on the primary structure of the protein, for example, task No. 2. Determine the primary structure of the synthesized protein if on a section of one DNA chain the nucleotides are located in the following sequence: GATACAATGGTTCGT.

1. Without disturbing the sequence, group the nucleotides into triplets: GAT - ACA - ATG - GTT - CGT.
2. Construct a complementary chain of mRNA: CUA - UGU - UAC - CAA - GC A.

PROBLEM SOLVING

3. According to the table genetic code identify the amino acids encoded by these triplets. Answer: lei-cis-tir-glu-ala. Similar types of problems are solved in a similar way based on the corresponding patterns and sequence of processes occurring in the cell.

Genetic problems are solved in the topic “Basic patterns of heredity.” These are problems on monohybrid, dihybrid crossing and other patterns of heredity, for example task No. 3. When black rabbits are crossed with each other, the offspring obtained are 3 black rabbits and 1 white. Determine the genotypes of parents and offspring.

1. Guided by the law of character splitting, identify the genes that determine the manifestation of dominant and recessive characters in this cross. Black suit - A, white - a;
2. Determine the genotypes of the parents (producing segregating offspring in a ratio of 3:1). Answer: Ah.
3. Using the hypothesis of gamete purity and the mechanism of meiosis, write a crossing diagram and determine the genotypes of the offspring.

Answer: the genotype of a white rabbit is aa, the genotypes of black rabbits are 1 AA, 2Aa.

Other genetic problems are solved in the same sequence, using appropriate patterns.

The temperature of the World Ocean significantly affects its biological diversity. This means that human activity could change the global distribution of life in the water, something that appears to already be happening with phytoplankton, which are declining by an average of 1% per year.

Ocean phytoplankton - single-celled microalgae - represent the basis of almost all food chains and ecosystems in the ocean. Half of all photosynthesis on Earth comes from phytoplankton. Its condition affects the amount of carbon dioxide the ocean can absorb, the abundance of fish, and ultimately the well-being of millions of people.

Term "biological diversity" means the variability of living organisms from all sources, including, but not limited to, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this concept includes diversity within species, between species and ecosystem diversity.

This is the definition of this term in the Convention on Biological Diversity. The objectives of this document are the conservation of biological diversity, the sustainable use of its components and the fair and equitable sharing of the benefits arising from the use of genetic resources.

Much research has previously been carried out on terrestrial biodiversity. Human knowledge about the distribution of marine fauna is significantly limited.

But the study, called the Census sea ​​life"(Census of Marine Life, about which Gazeta.Ru has repeatedly written), which lasted a decade, changed the situation. Man began to know more about the ocean. Its authors brought together knowledge of global trends in biodiversity across major groups of marine life, including corals, fish, whales, seals, sharks, mangroves, seaweeds and zooplankton.

“Although we are increasingly aware of global diversity gradients and associated environmental factors“Our knowledge of how these models work in the ocean lags significantly behind what we know about land, and this study was conducted to eliminate this discrepancy.”, - Walter Jetz from Yale University explained the purpose of the work.

Based on the data obtained, scientists compared and analyzed global patterns of biological diversity of more than 11 thousand marine species plants and animals, ranging from tiny plankton to sharks and whales.

Researchers have discovered striking similarities between the distribution patterns of animal species and ocean water temperatures.

These results mean that future changes in ocean temperature could significantly affect the distribution of marine life.

In addition, scientists found that the location of marine life diversity hotspots (areas where there are currently large numbers of rare species, which are in danger of extinction: such “points”, for example, are Coral reefs) mainly occurs in areas where it was recorded high level human impact. Examples of such impacts include fisheries, adaptation environment for their needs, anthropogenic climate change and environmental pollution. Perhaps humanity should think about how this activity fits within the framework of the Convention on Biological Diversity.

“The cumulative effect of human activity is threatening the diversity of life in the world’s oceans.”, says Camilo Mora from the University of Delhousie, one of the authors of the work.

Next to this work, another article was published in Nature on the problems of marine biological diversity on Earth. In it, Canadian scientists talk about the current colossal rate of decline in phytoplankton biomass in last years. Using archival data combined with the latest satellite observations, the researchers found that As a result of ocean warming, the amount of phytoplankton decreases by 1% per year.

Phytoplankton have the same size and abundance ratio as mammals

Phytoplankton is the part of plankton that carries out photosynthesis, primarily protococcal algae, diatoms and cyanobacteria. Phytoplankton are vitally important because they account for approximately half of the production of all organic matter on Earth and most of the oxygen in our atmosphere. In addition to a significant reduction in oxygen in the Earth’s atmosphere, which is still a long-term matter, the decline in phytoplankton numbers threatens changes in marine ecosystems, which will certainly affect fisheries.

When studying samples of marine phytoplankton, it turned out that what larger size cells of a particular type of algae, the lower their number. Surprisingly, this decrease in number occurs in proportion to the cell mass to the power of –0.75 - exactly the same quantitative ratio of these values ​​was previously described for terrestrial mammals. This means that the “rule of energy equivalence” also applies to phytoplankton.

Phytoplankton is distributed unevenly throughout the ocean. Its amount depends on the water temperature, lighting and amount nutrients. Cool years in temperate and polar regions are more suitable for phytoplankton development than warm years tropical waters. In the tropical zone of the open ocean, phytoplankton actively develops only where cold currents pass. In the Atlantic, phytoplankton actively develops in the area of ​​the Cape Verde Islands (not far from Africa), where the cold Canary Current forms a gyre.

In the tropics, the amount of phytoplankton is the same throughout the year, while in high latitudes there is an abundant proliferation of diatoms in spring and autumn and a strong decline in winter time. The largest mass of phytoplankton is concentrated in well-lit surface waters (up to 50 m). Deeper than 100 m, where it does not penetrate sunlight, there is almost no phytoplankton because photosynthesis is impossible there.

Nitrogen and phosphorus are the main nutrients necessary for the development of phytoplankton. They accumulate below 100 m, in a zone inaccessible to phytoplankton. If the water is well mixed, nitrogen and phosphorus are regularly delivered to the surface, feeding the phytoplankton. Warm waters lighter than cold ones and do not sink to depth - no mixing occurs. Therefore, in the tropics, nitrogen and phosphorus are not delivered to the surface, and the scarcity of nutrients prevents phytoplankton from developing.

In polar regions, surface waters cool and sink to depth. Deep currents carry cold waters to the equator. Bumping against underwater ridges, deep waters rise to the surface and carry minerals with them. In such areas there is much more phytoplankton. IN tropical zones in the open ocean, over the deep-sea plains (North American and Brazilian basins), where there is no rising water, there is very little phytoplankton. These areas are oceanic deserts and are avoided even by large migrating animals such as whales or sailboats.

Marine phytoplankton Trichodesmium is the most important nitrogen fixer in tropical and subtropical regions of the World Ocean. These tiny photosynthetic organisms use sunlight, carbon dioxide and other nutrients to synthesize organic matter, which forms the basis of the marine food pyramid. Nitrogen entering the upper illuminated layers of the ocean from the deep layers of the water column and from the atmosphere serves as a necessary feed for plankton.

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% earth's surface, but of the annual 170 billion tons of dry weight recorded as a result of 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 the ground and releases 80% of total number 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 the oceans occupy large area world, marine microorganisms can convert large amounts of inorganic carbon into organic carbon (the principle of photosynthesis). A big problem in the oceans - the availability of nutrients; they tend to deposit or react with water or other chemical compounds, 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.

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.