17.16: Major Oceanic Biomes - Biology

17.16: Major Oceanic Biomes - Biology

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Learning Objectives

  • Compare and contrast the characteristics of the ocean zones

The ocean is the largest marine biome. It is a continuous body of salt water that is relatively uniform in chemical composition; it is a weak solution of mineral salts and decayed biological matter. Within the ocean, coral reefs are a second kind of marine biome. Estuaries, coastal areas where salt water and fresh water mix, form a third unique marine biome.


The physical diversity of the ocean is a significant influence on plants, animals, and other organisms. The ocean is categorized into different zones based on how far light reaches into the water. Each zone has a distinct group of species adapted to the biotic and abiotic conditions particular to that zone.

The intertidal zone, which is the zone between high and low tide, is the oceanic region that is closest to land (Figure 1). Generally, most people think of this portion of the ocean as a sandy beach. In some cases, the intertidal zone is indeed a sandy beach, but it can also be rocky or muddy. The intertidal zone is an extremely variable environment because of tides. Organisms are exposed to air and sunlight at low tide and are underwater most of the time, especially during high tide. Therefore, living things that thrive in the intertidal zone are adapted to being dry for long periods of time. The shore of the intertidal zone is also repeatedly struck by waves, and the organisms found there are adapted to withstand damage from the pounding action of the waves (Figure 1). The exoskeletons of shoreline crustaceans (such as the shore crab, Carcinus maenas) are tough and protect them from desiccation (drying out) and wave damage. Another consequence of the pounding waves is that few algae and plants establish themselves in the constantly moving rocks, sand, or mud.

The neritic zone extends from the intertidal zone to depths of about 200 m (or 650 ft) at the edge of the continental shelf. Since light can penetrate this depth, photosynthesis can occur in the neritic zone. The water here contains silt and is well-oxygenated, low in pressure, and stable in temperature. Phytoplankton and floating Sargassum (a type of free-floating marine seaweed) provide a habitat for some sea life found in the neritic zone. Zooplankton, protists, small fishes, and shrimp are found in the neritic zone and are the base of the food chain for most of the world’s fisheries.

Beyond the neritic zone is the open ocean area known as the oceanic zone. Within the oceanic zone there is thermal stratification where warm and cold waters mix because of ocean currents. Abundant plankton serve as the base of the food chain for larger animals such as whales and dolphins. Nutrients are scarce and this is a relatively less productive part of the marine biome. When photosynthetic organisms and the protists and animals that feed on them die, their bodies fall to the bottom of the ocean where they remain; unlike freshwater lakes, the open ocean lacks a process for bringing the organic nutrients back up to the surface. The majority of organisms in the aphotic zone include sea cucumbers (phylum Echinodermata) and other organisms that survive on the nutrients contained in the dead bodies of organisms in the photic zone.

Beneath the pelagic zone is the benthic realm, the deepwater region beyond the continental shelf. The bottom of the benthic realm is comprised of sand, silt, and dead organisms. Temperature decreases, remaining above freezing, as water depth increases. This is a nutrient-rich portion of the ocean because of the dead organisms that fall from the upper layers of the ocean. Because of this high level of nutrients, a diversity of fungi, sponges, sea anemones, marine worms, sea stars, fishes, and bacteria exist.

The deepest part of the ocean is the abyssal zone, which is at depths of 4000 m or greater. The abyssal zone is very cold and has very high pressure, high oxygen content, and low nutrient content. There are a variety of invertebrates and fishes found in this zone, but the abyssal zone does not have plants because of the lack of light. Hydrothermal vents are found primarily in the abyssal zone; chemosynthetic bacteria utilize the hydrogen sulfide and other minerals emitted from the vents. These chemosynthetic bacteria use the hydrogen sulfide as an energy source and serve as the base of the food chain found in the abyssal zone.

Coral Reefs

Coral reefs are ocean ridges formed by marine invertebrates living in warm shallow waters within the photic zone of the ocean. They are found within 30˚ north and south of the equator. The Great Barrier Reef is a well-known reef system located several miles off the northeastern coast of Australia. Other coral reef systems are fringing islands, which are directly adjacent to land, or atolls, which are circular reef systems surrounding a former landmass that is now underwater. The coral organisms (members of phylum Cnidaria) are colonies of saltwater polyps that secrete a calcium carbonate skeleton. These calcium-rich skeletons slowly accumulate, forming the underwater reef.

Corals found in shallower waters (at a depth of approximately 60 m or about 200 ft) have a mutualistic relationship with photosynthetic unicellular algae. The relationship provides corals with the majority of the nutrition and the energy they require. The waters in which these corals live are nutritionally poor and, without this mutualism, it would not be possible for large corals to grow. Some corals living in deeper and colder water do not have a mutualistic relationship with algae; these corals attain energy and nutrients using stinging cells on their tentacles to capture prey.

It is estimated that more than 4,000 fish species inhabit coral reefs. These fishes can feed on coral, the cryptofauna (invertebrates found within the calcium carbonate substrate of the coral reefs), or the seaweed and algae that are associated with the coral. In addition, some fish species inhabit the boundaries of a coral reef; these species include predators, herbivores, or planktivores. Predators are animal species that hunt and are carnivores or “flesh eaters.” Herbivores eat plant material, and planktivores eat plankton.

Watch this National Oceanic and Atmospheric Administration (NOAA) video to see marine ecologist Dr. Peter Etnoyer discusses his research on coral organisms.

Try It

It takes a long time to build a coral reef. The animals that create coral reefs have evolved over millions of years, continuing to slowly deposit the calcium carbonate that forms their characteristic ocean homes. Bathed in warm tropical waters, the coral animals and their symbiotic algal partners evolved to survive at the upper limit of ocean water temperature.

Together, climate change and human activity pose dual threats to the long-term survival of the world’s coral reefs. As global warming due to fossil fuel emissions raises ocean temperatures, coral reefs are suffering. The excessive warmth causes the reefs to expel their symbiotic, food-producing algae, resulting in a phenomenon known as bleaching. When bleaching occurs, the reefs lose much of their characteristic color as the algae and the coral animals die if loss of the symbiotic zooxanthellae is prolonged.

Rising levels of atmospheric carbon dioxide further threaten the corals in other ways; as CO2 dissolves in ocean waters, it lowers the pH and increases ocean acidity. As acidity increases, it interferes with the calcification that normally occurs as coral animals build their calcium carbonate homes.

When a coral reef begins to die, species diversity plummets as animals lose food and shelter. Coral reefs are also economically important tourist destinations, so the decline of coral reefs poses a serious threat to coastal economies.

Human population growth has damaged corals in other ways, too. As human coastal populations increase, the runoff of sediment and agricultural chemicals has increased, too, causing some of the once-clear tropical waters to become cloudy. At the same time, overfishing of popular fish species has allowed the predator species that eat corals to go unchecked.

Although a rise in global temperatures of 1–2˚C (a conservative scientific projection) in the coming decades may not seem large, it is very significant to this biome. When change occurs rapidly, species can become extinct before evolution leads to new adaptations. Many scientists believe that global warming, with its rapid (in terms of evolutionary time) and inexorable increases in temperature, is tipping the balance beyond the point at which many of the world’s coral reefs can recover.

17 Unique Characteristics of The Ocean Biome

Ocean biome is one from many biome that exist on earth. As the biggest biome since the ocean area is bigger than land, then surely ocean biome has an important role to support the entire ecosystem both in the land and in the ocean it self. There are some biome on earth such as tundra, taiga, desert, and some other biome. To differentiate the ocean biome with another biome on earth there are some unique characteristics of the ocean biome that you need to know. And here I will give you some of the information.

1. The ocean water contains salt

As you all know that the ocean water taste salty because it contains salt. Every one gallon of ocean water contains about one cup of salt. The salinity level to each region is different to one another. And the marine animals or living beings also quite different to one another because of their ability to adapt.

2. Habitat for the largest animal on earth

Do you know what is the biggest or largest animal on earth? It is not elephant, or buffalo. But, it is known as blue whale! Whale for sure is an animal who lives in the ocean. And the ocean has become a home for many kind of species of whales.

3. Exist volcanic activity

Actually, the ocean experience volcanic activity more often compare to the land. This is why there is exist tsunami that we can see by eyes even though the volcanic activity can’t be seen.

4. Divided into several zones

The other unique characteristics of the ocean biome that you can find it by your self is the existence of the ocean layer. Our ocean is divided into several zone based on its depth. The zones are included epipelagic zone, mesopelagic zone, bathypelagic zone, abyssopelagic zone, and hadalpelagic zone.

5. Has another biome

Do you know that a biome can have another biome in it? Ocean biome has another biome inside of it, and one of them is the coral reef biome. Coral reef biome is a different biome because it has several different system that can support the last of the coral reef biome. If coral reef biome is classified as an ocean biome then it will be found in any depth but in fact, it is not.

6. The biggest biome

Because the ocean is bigger than the land, and it covers about 70% earth surface. And this is makes ocean biome become the biggest biome on earth compare to any other biome both in land and ocean.

7. Divided into some oceans

Ocean biome has a big area. And each area has their own characteristic that make it different to one another. Because the ocean is located in a different areas on earth, ocean is divided into some parts. We have about five oceans on earth and those are Pacific Ocean as the largest, Indian Ocean, Atlantic Ocean, Antarctic Ocean, and Arctic Ocean as the smallest ocean.

8. Diversity among the living beings

The diversity among the living beings also become the unique characteristics of the ocean biome. As what I have mentioned before that the ocean is so big until it is divided into several parts, and each part has its own characteristic. This become the factor that define the living beings that live inside of it because each living being will adapt to an environment they comfort in.

9. The temperature

Basically the ocean water temperature is stable but there are also some parts of the ocean that have a different temperature either it is hotter or colder. Just like the Arctic Ocean that has the coldest ocean water on earth. The temperature changing is caused by several factors. Even bad human act by cutting the trees also become one of the factor of the ocean water temperature changes. About the range of the ocean biome is different from one place to another but basically the range is about from -40°C to 50°C with the average of temperature about 39°C.

10. The tides phenomenon

Tides is a natural phenomenon of the rise and fall of the ocean water that you will usually see in the coast. The existence of tides is caused by some factors such as gravity. Fisherman who relies on the ocean as their source of money is being helped by the tides to sail to the open ocean.

11. Has about 20 million tons of gold

Even though most people will only know that the ocean has natural resources such as gold and oil but actually there is something else beneath the ocean. The ocean has about 20 million tons of gold that can be use to increase our economical condition for example. It also has another resource such as copper, nickel, mineral, and many more resources.

12. Absorbing heat

If you go to the ocean or sea to dive or simply just to swim, you will feel that when the sun rises and the temperature become hotter, the ocean water will not become colder. This condition is caused by the nature of ocean water which is to absorb 30% of heat. The heat absorbed by the ocean can affect the world climate through the water cycle system and also through the impact that might be brought by the ocean currents.

13. Bioluminescent

Bioluminescent is basically the ability of marine living being to produce the light from its body emission. This phenomenon is identic with the ocean biome. You can see this phenomenon happening when you go to the sea and sailing there in the night, and suddenly you will see the glowing ocean water . That glowing is being caused by the bioluminescent.

14. Estuaries

Estuaries also become the unique characteristics of the ocean biome. Basically, estuaries is a water body where the rivers meet the sea. In other words, estuaries also can be meant to be a place where the freshwater meet the saltwater. There is also exist a quite wide range of diversity in that place. The diversity exist because of the unite of saltwater and freshwater, which is something not so common.

15. Natural disaster

Ocean biome is also known because of its natural disaster phenomenon. There are several natural disaster that might happen in the ocean biome. The most popular one that you might also known is storm. The types of storm in the ocean biome also has so many variety and name.

Maybe most of the plants that live in the ocean doesn’t have the same exact size as the plants in the land. If you want to compare between the plants in the ocean and land than it will be the plants in the ocean has the smaller size. But do you know that about 70% of our oxygen is actually came from the plants in the ocean? So, by knowing this at least you know why you have to care about our ocean biome condition or at least to our environment.

17. Unexplored part

Last one, the unique characteristics of the ocean biome is its unexplored part. So, basically up to now humans are exploring only about 5% part of ocean biome. There is about 95% unexplored part that still become a mystery to solve. This is happening due to the several limitations such as technology, and the depth of the ocean as well.

So that’s all for the information that I can give you about the unique characteristics of the ocean biome. Thank you for being our loyal reader and follower, hopefully our article can help you to know more about the deep ocean facts. There will be more informative article for you to come.

Deep Sea Conservation

We thought it was really important to wrap up our discussion of the deep sea by reminding you that the deep sea is still prone to some destruction. In fact, deep sea trawlers are causing huge problems right now all around the world. They scrape the bottom of the ocean and pull up all the corals and bottom fauna. To get a better feel for the deep sea conservation, watch this short video we made.

Ocean Biome Flora and Fauna

The types of life that live in the ocean biome are extremely diverse. It is believed that this is the biome where live actually began. There are tons of types of fish found in the ocean biome. They include Angelfish, Blowfish, whales, and an assortment of sharks. You will find Octopus and crab living here.

For many of the large animals that live in the ocean biome, they help to keep it balanced for all of them. They consume many of the smaller animals so that they don’t get over populated. Since the temperatures in any ocean biome can be very cold, they have been able to adapt. For example whales have thick layers of fat known as blubber. This helps them to keep their body temperature where it should be.

The Blue Whale is the largest mammal in the world, and belongs to the ocean biome. Due to the enormous size of such an environment though these animals have plenty of room to move around and thrive. There are millions of types of aquatic life found in the ocean biome. It is amazing to compare some of the single cell microorganisms there to the size of the Blue Whale.

The corral is very active in the ocean biome. Jellyfish may be found as well as lobster and turtles. What you will find really depends on the area of the ocean biome. Some of these living things are close to the surface. Others remain deep down in the murky waters so they are rarely seen. There are animals in the ocean biome that live close to shore and those that are many miles from land.

Ocean Biome Characteristics

3. Ocean Acidification Sending Us Back 17 Million Years

Ocean acidification is no small issue. The basic science behind acidification is that the ocean absorbs CO2 through natural processes, but at the rate at which we're pumping it into the atmosphere through burning fossil fuels, the ocean's pH balance is dropping to the point where some life within the oceans are having trouble coping.  

According to NOAA, it is estimated that by the end of this century, surface levels of the oceans could have a pH of about 7.8 (in 2020 the pH level is 8.1). "The last time the ocean pH was this low was during the middle Miocene, 14-17 million years ago. The Earth was several degrees warmer and a major extinction event was occurring."

Freaky, right? At some point in time, there is a tipping point where the oceans become too acidic to support life that can't quickly adjust. In other words, many species are going to be wiped out, from shellfish to corals and the fish that depend on them.

8 Major Biomes of the World | Ecology

The following points highlight the eight major biomes of the world. The biomes are: 1. Tundra 2. Northern Conifer Forest 3. Temperate Deciduous Forests 4. Tropical Rain Forest 5. Chapparal 6. Tropical Savannah 7. Grassland 8. Desert.

Biome # 1. Tundra:

The literal meaning of word Tundra is north of the timberline. The tundra extends above 60°N latitude. It is almost treeless plain in the far northern parts of Asia, Europe and North America. A tundra consists of plains characterised by snow, ice and frozen soil most of the year. The permanent frozen soil of tundra is called permafrost.

Winters are very long on the tundra with little daylight. In contrast summers are short but there are many daylight hours. Precipitation is low, amounting to only 25 cm or less per year, because cold air can hold relatively little moisture.

The ground is soggy in the summer because moisture cannot soak into the permanently frozen ground. Ponds, small lakes and marshes are abundant due to the nearly flat terrain.

There are no upright trees on the tundra. Only trees such as dwarf willows and birches, which grow low to the ground, can escape the drying effect of the wind which upright trees would experience. This biome consists mainly of mosses, grasses, sedges, lichens and some shrubs. Seasonal thawing of the frozen soil occurs only up-to a few centimetres depth, which permits the growth of shallow rooted plants.

Carbon, arctic hare and musk ox are important herbivores of tundra biome. Some important carnivores that prey on the herbivores are the arctic fox, arctic wolf, bobcat and snowy owl. Polar bears live along coastal areas, and prey on seals.

Because of the severe winters, many of the animals are migratory and move from one region to another with the change in seasons. Many shorebirds and water fowls, such as ducks and geese, nest on the tundra during the summer but migrate south for the winter. The tundra make a very delicate ecosystem, and may be recovered from any disturbance very slowly.

Biome # 2. Northern Conifer Forest:

The northern coniferous forest or taiga is a 1300-1450 km wide band south of the tundra. This extends as an east-west band across North America, Europe and Asia. This area also has long, cold winters, but summer temperatures may reach 10-12°C, and the summer and the growing season are longer than in the tundra. Precipitation is higher than in the tundra, ranging from 10 to 35 cm annually.

The moisture is the combined result of summer rains and winter snows. Lakes, ponds and bogs are abundant. The duration of growing period of plants is only about 150 days. Since five physical conditions are variable, the organisms are resistant to fluctuations of temperature.

The taiga makes really a northern forest of coniferous trees such as spruce, fir, pine, cedar and hemlock. In disturbed areas, deciduous trees such as birch, willow and poplar are abundant. In certain areas the trees are so dense that little light may reach the floor of the forest. Vines, maple and spring wild flowers are common. Mosses and ferns also grow in moist areas.

The common smaller mammals are herbivores, such as squirrels, snowshoe hare, and predatory martens. Important migratory herbivores include moose, elk, deer and carbon. Moose and carbon migrate to the taiga for winters and to the tundra for summers.

Important predators are the timber wolf, grizzly bear, black bear, bobcat and wolverine. Many insects are found during the warmer months. Migratory shore birds and waterfowls are abundant during summer months.

Biome # 3. Temperate Deciduous Forests:

The deciduous forests are found in the temperate regions of north central Europe, east Asia and the eastern United States, that is, south of the taiga in the Northern Hemisphere. Such forests occur in regions having hot summers, cold winter, rich soil and abundant rain. Annual rainfall is typically around 100 cm per year.

Common deciduous trees are the hardwoods such as beech, maple, oak, hickory and walnut. They are broad-leaved trees. The trees shed their leaves in the late fall so the biome has an entirely different appearance in the winter than in the summer.

The fallen leaves provide food for a large variety of consumer and decomposer populations, such as millipedes, snails and fungi living in or on the soil. The temperate deciduous forest produces flowers, fruits and seeds of many types which provide a variety of food for animals.

The common herbivores of this biome are deer, chipmunks, squirrels, rabbits and beavers. Tree-dwelling birds are abundant in number and diversity. Important predators are—black bears, bobcats, and foxes. Predatory birds are also found, such as hawks, owls and eagles. The cold­blooded or ectothermic animals, such as snakes, lizards, frogs, and salamanders are also common.

The temperate deciduous forest makes a very complex biome. Many changes take place during the year, and a large variety of species inhabit the soil, trees and air.

Biome # 4. Tropical Rain Forest:

This biome is situated in the equatorial regions having the annual rainfall more than 140 cm. However, the tropical rain forest makes an important biome across the earth as a whole. This biome is found in Central America, the Amazon Basin, Orinocon Basin of South America, Central Africa, India and Southeast Asia.

Tropical rain forests have high rainfall, high temperature all year, and a great variety of vegetation. Plant life is highly diverse reaching up-to a framework of 200 species of trees per hectare. The warm, humid climate supports broad- leaved evergreen plants showing peculiar stratification into an upper storey and two or three understoreys.

The tallest trees make an open canopy, but the understoreyed plants block most of the light from the jungle floor. The climbers and lianas reach the highest level of the trees in search of light.

An enormous variety of animals lives in the rain forest, such as insects, lizards, snakes, monkeys and colorful birds. The ant eaters, bats, large carnivorous animals, and a variety of fish in the rivers are quite common. About 70-80 per cent of the known insects are found in tropical rain forests. Such rich animal diversity is linked to plant-animal interaction for pollination and dispersal of fruits and seeds.

Biome # 5. Chapparal:

This biome is also known as mediterranian scrub forest. This is marked by limited winter rain followed by drought in the rest of the year. The temperature is moderate under the influence of cool, moist air of the oceans. The biome extends along the mediterranian.

Pacific coast of North America, Chile, South Africa and South Australia. This biome has broad-leaved evergreen vegetation. The vegetation is generally made up of fire resistant resinous plants and drought-adapted animals. Bush fires are very common in this biome.

Biome # 6. Tropical Savannah:

The savannahs are warm climate plants characterized by coarse grass and scattered trees on the margins of tropics having seasonal rainfall. Primarily they are situated in South America, Africa and Australia. However, there is no savannah vegetation in India. The average total rainfall in such regions is 100 to 150 cm. There is alternation of wet and dry seasons.

Plants and animals are drought tolerant and do not have much diversity. The animal life of tropical savannah biome consists of hoofed herbivorous species, such as giraffe, zebra, elephant, rhinoceros and several kinds of antelope. Kangaroos are found in the savannahs of Australia.

Biome # 7. Grassland:

Some grasslands occur in temperate areas of the earth and some occur in tropical regions. Temperate grasslands usually possess deep, rich soil. They have hot summers cold winters and irregular rainfall. Often they are characterized by high winds. The main grasslands include the prairies of Canada and U.S.A., the pampas of South America, the steppes of Europe and Asia, and the veldts of Africa.

The dominant plant species comprise short and tall grasses. In tall-grasses prairies in the United States, important grasses are tall bluestem, Indian grass and slough grass. Short-grass prairies generally have blue grama grass, mesquite grass and bluegrass. Many grasses have long, well-developed root systems which enable them to survive limited rainfall and the effects of fire.

The main animals of this biome are-the prong-horned antelopes, bison, wild horse, jack rabbit, ground squirrel and prairie dogs. Larks, the burrowing owl and badgers are also found. Important grassland predators include coyotes, foxes, hawks and snakes.

Biome # 8. Desert:

The desert biome is characterised by its very low rainfall, which is usually 25 cm per year or less. Most of this limited moisture comes as short, hard showers. Primarily the deserts of the world are located in the south-west U.S.A., Mexico, Chile, Peru, North Africa (Sahara desert), Asia (Tibet Gobi Thar) and central Western Australia. Deserts generally have hot days and cold nights, and they often have high winds.

The reason for the difference of temperature between day and night is due to the lack of water vapour in the air. Deserts are characterised by scanty flora and fauna. Desert organisms must meet some initial requirements if they are to survive. The plants must be able to obtain and conserve water.

In order to meet these requirements, many adaptations have been made by desert plants. Such adaptations are—reduced leaf surface area, which reduces evaporation from the plants, loss of leaves during long dry spell small hairs on the leaf surfaces, and the ability to store large amount of water.

The examples of important desert plants are—yuccas, acacias, euphorbias, cacti, many other succulents and hardy grasses. Many of the small plants are annuals.

Animals also must meet the requirements of heat, cold and limited water. Many desert animals are nocturnal in habit, and are active mainly at night. Many reptiles and small mammals burrow to get away from the intense heat of midday. The other common desert animals are the herbivorous kangaroo, rat, ground squirrel, and jack rabbit.

The important predators are—coyotes, badgers, kit fox, eagles, hawks, falcons and owls. Ants, locusts, wasps, scorpions, spiders, insect-eating birds, such as swifts and swallows, seed-eating quails, doves and various cats are other common desert animals.

17.16: Major Oceanic Biomes - Biology

Major Biomes Of North America

Biome: A large geographical region whose climate produces a characteristic climax association of plants and animals. The term biome usually refers to terrestrial habitats (on land). In North America there are about six major biomes. Aquatic ecosystems, such as the ocean, are often subdivided into different zones, such as the intertidal, pelagic, benthic, photic and aphotic zones.

Plant Community: An assemblage or association of certain dominant indicator species occupying a given region. In California the desert biome consists of several different plant communities, such as the creosote bush scrub, shadscale scrub, sagebrush scrub, Joshua tree woodland and pinyon-juniper woodland. The local chaparral and coastal sage scrub plant communities surrounding Palomar College are condidered part of an arid desert biome. Some general biology textbooks have added a seventh biome called the "shrubland biome" to encompass these brushy habitats.

Chaparral: A plant community composed of dense, impenetrable, shrubby vegetation adapted to a Mediterranean climate with winter-wet and summer-dry seasons. The plant community is well-developed in the mountains of San Diego County. Following periodic brush fires, many of the shrub species resprout from subterranean lignotubers.

Coastal Sage Scrub: A plant community similar to the chaparral, but typically found at lower elevations (generally below 2,000 feet). It is dominated by aromatic coastal sagebrush ( Artemisia californica ) and black sage (Salvia mellifera), and is common in the hills bordering Palomar College. Unfortunately, this plant community is prime land for developers and is rapidly being replaced by housing developments in San Diego County. It is now (2001) considered to be an endangered (threatened) plant community in southern California.

Shrubs of the coastal sage scrub are adapted to the long, dry summers in several ways. Remaining dormant throughout the dry season, they may lose 80% of their water. During this time they may drop many of their brittle, shriveled leaves or produce smaller leaves on secondary shoots. Root systems are generally shallow because the plants are inactive much of the time. It is relatively easy to clear away desiccated shrubs with a heavy hoe during the summer drought season, compared with well-anchored shrubs of true chaparral. The oily, resinous leaves also help to conserve vital moisture, but increase their flammability. The dominant shrubs are fire adapted with seeds that readily germinate after fire. This also includes numerous species of post burn wildflowers that bloom in profusion following the winter and spring rains. Unlike scattered laurel sumac (Malosma laurina) and lemonade berry (Rhus integrifolia), the dominant semi-woody shrubs (mostly Artemisia, Salvia, & Eriogonum) lack lignotubers and rely on seeds for regeneration after fire. These shrubs are vulnerable to excessive or poorly-timed fires, particularly when competing with naturalized grasses and other weedy species. The common vine throughout the coastal sage scrub called wild cucumber ( Marah macrocarpus ) sprouts soon after fires from a large, subterranean caudex. Under ideal natural conditions, complete recovery of coastal sage scrub after a fire is about 15 to 20 years.

Ecosystem: All of the organisms in a natural community or biome plus all of the associated environmental factors with which they interact. The term ecosystem could actually be applied to any of the terrestrial biomes or plant communities. For example, the tundra biome could also be referred to as tundra ecosystem the chaparral plant community could also be referred to as the chaparral ecosystem. The term ecosystem is well-suited for aquatic communities such as ponds, lakes, streams and even the ocean. In fact, oceanography is the study of the ocean ecosystem. Including ocean, topsoil and atmosphere, the earth is a large, complex ecosystem called the biosphere however, in terms of the vast universe it is but a mere dot. A self-contained spaceship in which gasses and waste are recycled may also be thought of as an ecosystem.

Biosphere: (Earth Ecosystem): The zone of atmosphere, land and water at the surface of the earth occupied by living things. In grave danger by the effects of humans, including overpopulation, pollution and exploitation.

Environment: The sum total of physical and biotic factors that surround an organism or population of organisms.

17.16: Major Oceanic Biomes - Biology

The biosphere is one of Earth’s four interconnected systems.

I. The biosphere is the portion of Earth that is inhabited by life.

A. The biosphere includes all ecosystems.

  • 3. hydrosphere —water, ice, and water vapor
  • 4. atmosphere —air blanketing Earth’s solid and liquid surface
  • 5. geosphere —geologic features above and below Earth’s surface

B. Biotic and abiotic factors interact in the biosphere .

Copyright Pearson Prentice Hall

Photo Credit: ©Michael Fogden/DRK PHOTO

Copyright Pearson Prentice Hall

    • 2. Plants and animals exhibit variations in tolerance , (ability to survive and reproduce under conditions that differ from their optimal conditions).

    Copyright Pearson Prentice Hall

      • A. Climate of a region is an important factor in determining which organisms can survive there.
      • B. Within a biome, temperature and precipitation can vary over small distances.
      • C. The climate in a small area that differs from the climate around it is called a microclimate .

      Copyright Pearson Prentice Hall

      D. Biomes are defined by a unique set of abiotic factors

      2. Characteristic assemblage of plants and animals

      Copyright Pearson Prentice Hall

      Copyright Pearson Prentice Hall

      Temperate woodland
      and shrubland

      This map shows the locations of the world’s major biomes. Other parts of Earth’s surface are classified as mountains or ice caps. Each biome has a characteristic climate and community of organisms.

      • 1. Produce lush forests
      • 2. Home to more species than all other biomes combined.
      • 3. Canopy- dense covering 50-80 m above forest floor.

      Copyright Pearson Prentice Hall

      4. Understory - the shade below the canopy, a second layer of shorter trees and vines.

      5. Organic matter that falls to the forest floor quickly decomposes, and the nutrients are recycled.

      Copyright Pearson Prentice Hall

      b. thin, nutrient-poor soils

      7. Dominant plants: broad-leaved evergreen trees ferns large woody vines and climbing plants

      Copyright Pearson Prentice Hall

      Source: World Meteorological Organization

      8. Dominant wildlife: sloths, capybaras, jaguars, anteaters, monkeys, toucans, parrots, butterflies, beetles, piranhas, caymans, boa constrictors, and anacondas.

      9. Geographic distribution: parts of South and Central America, Southeast Asia, parts of Africa, southern India, and northeastern Australia

      Copyright Pearson Prentice Hall

      • B.Tropical Dry Forest
        • 1. Grow in places where rainfall is highly seasonal rather than year-round.
        • 2. During the dry season, nearly all the trees drop their leaves to conserve water.- deciduous.

        Copyright Pearson Prentice Hall

        a. generally warm year-round

        b. alternating wet and dry seasons

        c. rich soils subject to erosion

        4. Dominant plants: tall, deciduous trees drought-tolerant plants aloes and other succulents

        Copyright Pearson Prentice Hall

        5. Dominant wildlife: tigers, monkeys, elephants, Indian rhinoceroses, hog deer, great pied hornbills, pied harriers, spot-billed pelicans, termites, snakes and monitor lizards

        6. Geographic distribution: parts of Africa, South and Central America, Mexico, India, Australia, and tropical islands

        Copyright Pearson Prentice Hall

        • C.Tropical Savanna
          • 1. Or grasslands , receive more rainfall than deserts but less than tropical dry forests.
          • 2. They are covered with grasses.
          • 3. Compact soils, fairly frequent fires, and the action of large animals prevent them from becoming dry forest.

          Copyright Pearson Prentice Hall

          d. frequent fires set by lightning

          5. Dominant plants: tall, perennial grasses drought-tolerant and fire-resistant trees or shrubs

          Copyright Pearson Prentice Hall

          Dominant wildlife: lions, leopards, cheetahs, hyenas, jackals, aardvarks, elephants, giraffes, antelopes, zebras, baboons, eagles, ostriches, weaver birds, and storks

          Geographic distribution: large parts of eastern Africa, southern Brazil, and northern Australia

          Copyright Pearson Prentice Hall

          • E. Temperate Grassland
            • 1. Rich mix of grasses and underlaid by fertile soils.
            • 2. Periodic fires and heavy grazing by large herbivores maintain the characteristic plant community.

            Copyright Pearson Prentice Hall

            4. Dominant plants: lush, perennial grasses and herbs most are resistant to drought, fire, and cold

            Copyright Pearson Prentice Hall

            Source: National Oceanic Atmospheric Administration

            6. Dominant wildlife: mountain lions, gray foxes, bobcats, mule deer, pronghorn antelopes, desert bighorn sheep, kangaroo rats, bats, owls, hawks, roadrunners, ants, beetles, butterflies, flies, wasps, tortoises, rattlesnakes, and lizards

            7. Geographic distribution: Africa, Asia, the Middle East, United States, Mexico, South America, and Australia

            Aquatic Biomes

            Terrestrial organisms are generally limited by temperature and moisture. Therefore, terrestrial biomes are defined in terms of these abiotic factors. In contrast, most organisms that live in the water do not have to deal with extremes of temperature or moisture. Instead, their main limiting factors are the availability of sunlight and the concentration of dissolved nutrients in the water.

            What are Aquatic Biomes

            Aquatic biomes are biomes found in water. Water covers 70 percent of Earth’s surface, so aquatic biomes are a major component of the biosphere. However, they have less total biomass than terrestrial biomes. Aquatic biomes can occur in either salt water or freshwater. About 98 percent of Earth’s water is salty, and only 2 percent is fresh. The primary saltwater biome is the ocean. Major freshwater biomes include lakes and rivers.

            Aquatic Zones

            In large bodies of standing water (including the ocean and lakes), the water can be divided into zones based on the amount of sunlight it receives. There is enough sunlight for photosynthesis only in - at most - the top 200 meters of water. Water down to this depth is called the photic zone. Deeper water, where too little sunlight penetrates for photosynthesis, is called the aphotic zone.

            Surface water dissolves oxygen from the air, so there is generally plenty of oxygen in the photic zone to support organisms. Water near shore usually contains more dissolved nutrients than water farther from the shore. This is because most dissolved nutrients enter a body of water from land, carried by runoff or rivers that empty into the body of water. When aquatic organisms die, they sink to the bottom, where decomposers release the nutrients they contain. As a result, deep water may contain more nutrients than surface water.

            Deep ocean water may be forced to the surface by currents in a process called '''upwelling.''' When this happens, dissolved nutrients are brought to the surface from the deep ocean. The nutrients can support large populations of producers and consumers, including many species of fish. As a result, areas of upwelling are important for commercial fishing.With these variations in sunlight, oxygen, and nutrients, different parts of the ocean or a lake have different types and numbers of organisms. Therefore, life in a lake or the ocean is generally divided into zones. The zones correlate mainly with the amount of sunlight and nutrients available to producers. Figure 1 shows ocean zones. Lakes have similar zones.

            • The littoral zone is the shallow water near the shore. In the ocean, the littoral zone is also called the intertidal zone. • The pelagic zone is the main body of open water farther out from shore. It is divided into additional zones based on water depth. In the ocean, the part of the pelagic zone over the continental shelf is called the neritic zone, and the rest of the pelagic zone is called the oceanic zone. • The benthic zone is the bottom surface of a body of water. In the ocean, the benthic zone is divided into additional zones based on depth below sea level.

            Figure 1: The ocean is divided into many different zones, depending on distance from shore and depth of water. The pelagic zone is divided into neritic and oceanic zones based on distance from shore. Into what additional zones is the pelagic zone divided on the basis of water depth? What additional zones make up the benthic zone?

            Aquatic Organisms

            Aquatic organisms are classified into three basic categories: plankton, nekton, and benthos. Organisms in these three categories vary in where they live and how they move.

            Plankton are aquatic organisms that live in the water itself and cannot propel themselves through water. They include both phytoplankton and zooplankton. Phytoplankton are bacteria and algae that use sunlight to make food by photosynthesis. Zooplankton are tiny animals that feed on phytoplankton.

            Nekton are aquatic animals that live in the water and can propel themselves by swimming or other means. Nekton include invertebrates such as shrimp and vertebrates such as fish.

            Benthos are aquatic organisms that live on the surface below a body of water. They live in or on the sediments at the bottom. Benthos include sponges, clams, and sea stars (see Figure 2).

            Figure 2: This sea star, or starfish, is an example of a benthic organism. The tiny white projections on the bottom surface of the sea star allow it anchor to, or slowly crawl over, the bottom surface of the ocean.

            Marine Biomes

            Marine biomes are aquatic biomes found in the salt water of the ocean. Major marine biomes are neritic, oceanic, and benthic biomes. Other marine biomes include intertidal zones, estuaries, and coral reefs.

            Neritic Biomes

            Neritic biomes occur in ocean water over the continental shelf (see Figure 1). They extend from the low-tide water line to the edge of the continental shelf. The water here is shallow, so there is enough sunlight for photosynthesis. The water is also rich in nutrients, which are washed into the water from the nearby land. Because of these favorable conditions, large populations of phytoplankton live in neritic biomes. They produce enough food to support many other organisms, including both zooplankton and nekton. As a result, neritic biomes have relatively great biomass and biodiversity. They are occupied by many species of invertebrates and fish. In fact, most of the world’s major saltwater fishing areas are in neritic biomes.

            Oceanic Biomes

            Oceanic biomes occur in the open ocean beyond the continental shelf. There are lower concentrations of dissolved nutrients away from shore, so the oceanic zone has a lower density of organisms than the neritic zone. The oceanic zone is divided into additional zones based on water depth (see Figure 1).

            • The epipelagic zone is the top 200 meters of water, or the depth to which enough sunlight can penetrate for photosynthesis. Most open ocean organisms are concentrated in this zone, including both plankton and nekton.

            • The mesopelagic zone is between 200 and 1,000 meters below sea level. Some sunlight penetrates to this depth but not enough for photosynthesis. Organisms in this zone consume food drifting down from the epipelagic zone, or they prey upon other organisms in their own zone. Some organisms are detrivores, which consume dead organisms and organic debris that also drift down through the water.

            • The bathypelagic zone is between 1,000 and 4,000 meters below sea level. No sunlight penetrates below 1,000 meters, so this zone is completely dark. Most organisms in this zone either consume dead organisms drifting down from above or prey upon other animals in their own zone. There are fewer organisms and less biomass here than in higher zones. Some animals are bioluminescent, which means they can give off light (see Figure 3). This is an adaptation to the total darkness.

            • The abyssopelagic zone is between 4,000 and 6,000 meters below sea level. The hadopelagic zone is found in the water of deep ocean trenches below 6,000 meters. Both of these zones are similar to the bathypelagic zone in being completely dark. They have even lower biomass and species diversity.

            Figure 3: The anglerfish lives in the bathypelagic zone. The rod-like structure protruding from the anglerfish’s face is tipped with bioluminescent microorganisms. The structure wiggles like a worm to attract prey. Only the ”worm” is visible to prey in the total darkness of this zone.

            Benthic Biomes

            Benthic biomes occur on the bottom of the ocean where benthos live. Some benthos, including sponges, are sessile, or unable to move, and live attached to the ocean floor. Other benthos, including clams, burrow into sediments on the ocean floor. The benthic zone can be divided into additional zones based on how far below sea level the ocean floor is (see Figure 1).

            • The sublittoral zone is the part of the ocean floor that makes up the continental shelf near the shoreline. The water is shallow enough for sunlight to penetrate down to the ocean floor. Therefore, photosynthetic producers such as seaweed can grow on the ocean floor in this zone. The littoral zone is rich in marine life.

            • The bathyal zone is the part of the ocean floor that makes up the continental slope. It ranges from about 1,000 to 4,000 meters below sea level. The bathyal zone contains no producers because it is too far below the surface for sunlight to penetrate. Although consumers and decomposers live in this zone, there are fewer organisms here than in the sublittoral zone.

            • The abyssal zone is the part of the ocean floor in the deep open ocean. It varies from about 4,000 to 6,000 meters below sea level. Organisms that live on the ocean floor in this zone must be able to withstand extreme water pressure, continuous cold, and scarcity of nutrients. Many of the organisms sift through sediments on the ocean floor for food or dead organisms.

            • The hadal zone is the ocean floor below 6,000 meters in deep ocean trenches. The only places where organisms are known to live in this zone are at hydrothermal vents, where invertebrates such as tubeworms and clams are found. They depend on microscopic archaea organisms for food. These tiny chemosynthetic producers obtain energy from chemicals leaving the vents.

            Intertidal Zone

            The intertidal zone is a narrow strip along the coastline that falls between high- and lowtide water lines. It is also called the littoral zone (see Figure 1). A dominant feature of this zone is the regular movement of the tides in and out. In most areas, this occurs twice a day. Due to the tides, this zone alternates between being under water at high tide and being exposed to the air at low tide. An intertidal zone is pictured in Figure 4.

            Figure 4: These pictures show the Bay of Fundy off the northeastern coast of Maine in North America. The picture on the left shows the bay at high tide, and the picture on the right shows the bay at low tide. The area covered by water at high tide and exposed to air at low tide is the intertidal zone.

            The high tide repeatedly brings in coastal water with its rich load of dissolved nutrients. There is also plenty of sunlight for photosynthesis. In addition, the shallow water keeps large predators, such as whales and big fish, out of the intertidal zone. As a result, the intertidal zone has a high density of living things. Seaweeds and algae are numerous, and they support many consumer species, either directly or indirectly, including barnacles, sea stars, and crabs.

            Other conditions in the intertidal zone are less favorable. For example, there are frequent shifts from a water to an air environment. There are also repeated changes in temperature and salinity (salt concentration). These changing conditions pose serious challenges to marine organisms. The moving water poses yet another challenge. Organisms must have some way to prevent being washed out to sea with the tides. Barnacles, like those in Figure 5, cement themselves to rocks. Seaweeds have rootlike structures, called holdfasts, which anchor them to rocks. Crabs burrow underground to avoid being washed out with the tides.

            Figure 5: Barnacles secrete a cement-like substance that anchors them to rocks.

            Other Marine Biomes

            The intertidal zone has high biodiversity. However, it is not the marine biome with the highest biodiversity. That distinction goes to estuaries and coral reefs. They have the highest biodiversity of all marine biomes.

            • An estuary is a bay where a river empties into the ocean. It is usually semi-enclosed, making it a protected environment. The water is rich in dissolved nutrients from the river and shallow enough for sunlight to penetrate for photosynthesis. As a result, estuaries are full of marine life. Figure 6 shows an estuary on the California coast near San Francisco.

            Figure 6: This satellite photo shows the San Francisco Estuary on the California coast. This is the largest estuary on the lower west coast of North America. Two rivers, the Sacramento and the San Joaquin, flow into the estuary (upper right corner of photo). The estuary is almost completely enclosed by land but still connected to the ocean.

            • A coral reef is an underwater limestone structure produced by tiny invertebrate animals called corals. Coral reefs are found only in shallow, tropical ocean water. Corals secrete calcium carbonate (limestone) to form an external skeleton. Corals live in colonies, and the skeletal material gradually accumulates to form a reef. Coral reefs are rich with marine organisms, including more than 4,000 species of tropical fish. Figure 7 shows a coral reef in the Hawaiian Islands.

            Figure 7: Colorful fish swim in warm, shallow ocean water near a coral reef off the Hawaiian Islands.

            Freshwater Biomes

            Freshwater biomes occur in water that contains little or no salt. Freshwater biomes include standing water and running water biomes.

            Standing Freshwater Biomes

            Standing freshwater biomes include ponds and lakes. Ponds are generally smaller than lakes and shallow enough for sunlight to reach all the way to the bottom. In lakes, at least some of the water is too deep for sunlight to penetrate. As a result, like the ocean, lakes can be divided into zones based on availability of sunlight for producers.

            • The littoral zone is the water closest to shore. The water in the littoral zone is generally shallow enough for sunlight to penetrate, allowing photosynthesis. Producers in this zone include both phytoplankton and plants that float in the water. They provide food, oxygen, and habitat to other aquatic organisms. The littoral zone generally has high productivity and high biodiversity.

            • The limnetic zone is the top layer of lake water away from shore. This zone covers much of the lake’s surface, but it is only as deep as sunlight can penetrate. This is a maximum of 200 meters. If the water is muddy or cloudy, sunlight cannot penetrate as deeply. Photosynthesis occurs in this zone, and the primary producers are phytoplankton, which float suspended in the water. Zooplankton and nekton are also found in this zone. The limnetic zone is generally lower in productivity and biodiversity than the littoral zone.

            • The profundal zone is the deep water near the bottom of a lake where no sunlight penetrates. Photosynthesis cannot take place, so there are no producers in this zone. Consumers eat food that drifts down from above, or they eat other organisms in the profundal zone. Decomposers break down dead organisms that drift down through the water. This zone has low biodiversity.

            • The benthic zone is the bottom of a lake. Near the shore, where water is shallow, the bottom of the lake receives sunlight, and plants can grow in sediments there. Organisms such as crayfish, snails, and insects also live in and around the plants near shore. The plants provide shelter from predatory fish as well as food and oxygen. In deeper water, where the bottom of the lake is completely dark, there are no producers. Most organisms that live here are decomposers.

            The surface water of a lake is heated by sunlight and becomes warmer than water near the bottom. Because warm water is less dense that cold water, it remains on the surface. When dead organisms sink to the bottom of a lake, they are broken down by decomposers that release the nutrients from the dead organism. As a result, nutrients accumulate at the lake’s bottom. In spring and fall in temperate climates, the surface water of a lake reaches the same temperature as the deeper water. This gives the different water layers the same density, allowing them to intermix. This process, called turnover, brings nutrients from the bottom of the lake to the surface, where producers can use them.

            Lakes can be categorized on the basis of their overall nutrient levels, as shown in Table 1. Oligotrophic lakes have low nutrient levels, so they also have low productivity. With few producers (or other aquatic organisms), the water remains clear and little oxygen is used up to support life. Biodiversity is low.

            Table 1: Trophic Classification of Freshwater Lakes

            Acid rain is another cause of low productivity in lakes. Acid rain falling into a lake causes the lake water to become too acidic for many species to tolerate. This results in a decline in the number and diversity of lake organisms. This has happened to many lakes throughout the northeastern United States. The water in the lakes is very clear because it is virtually devoid of life.Lakes with high nutrient levels have higher productivity, cloudier water, lower oxygen levels, and higher biomass and biodiversity. Very high nutrient levels in lakes are generally caused by contamination with fertilizer or sewage. The high concentration of nutrients may cause a massive increase in phytoplankton, called a phytoplankton bloom (see Figure 8). The bloom blocks sunlight from submerged plants and other producers and negatively impacts most organisms in the lake.

            Figure 8: The phytoplankton bloom on this lake blocks most sunlight from penetrating below the surface, creating a condition detrimental to many other aquatic organisms.

            Running Freshwater Biomes

            Running freshwater biomes include streams and rivers. Streams are generally smaller than rivers. Streams may start with surface runoff, snowmelt from a glacier, or water seeping out of the ground from a spring. If the land is not flat, the water runs downhill. The water joins other streams and then rivers as it flows over the land. Eventually, the water empties into a pond, lake, or the ocean.

            Some species living in rivers that empty into the ocean may live in freshwater during some stages of their life cycle and in salt water during other stages. For example, salmon are born and develop in freshwater rivers and then move downstream to the ocean, where they live as adults. In contrast, some eels are born and develop in the ocean and then move into freshwater rivers to live as adults.Compared with standing water, running water is better able to dissolve oxygen needed by producers and other aquatic organisms. When a river rushes over a waterfall, like the one in Figure 9, most of the water is exposed to the air, allowing it to dissolve a great deal of oxygen. Flowing water also provides a continuous supply of nutrients. Some nutrients come from the decomposition of dead aquatic organisms. Other nutrients come from the decomposition of dead terrestrial organisms, and other organic debris such as leaves, that fall into the water.

            Figure 9: Flowing water forms a waterfall on the South Yuba River in Nevada County, California. As the water falls through the air, it dissolves oxygen needed by aquatic organisms.

            Algae are the main producers in running freshwater biomes. If water flows slowly, algae can float suspended in the water, and huge populations may form, like the phytoplankton bloom in Figure 8 above. If water flows rapidly, algae must attach themselves to rocks or plants to avoid being washed away and generally cannot form very large populations.

            Plants are also important producers in most running water biomes. Some plants, such as mosses, cling to rocks. Other plants, such as duckweed, float in the water. If nutrient levels are high, floating plants may form a thick mat on the surface of the water, like the one shown in Figure 10 (left photo). Still other plants grow in sediments on the bottoms of streams and rivers. Many of these plants—like the cattails in Figure 10 (right photo)—have long narrow leaves that offer little resistance to the current. In addition to serving as a food source, plants in running water provide aquatic animals with protection from the current and places to hide from predators.

            Figure 10: The picture on the left shows a thick mat of duckweed floating on a river. The picture on the right shows cattails growing in sediments at the edge of a stream bed. Notice the cattails’ long, slender leaves, which reduce water resistance.

            Consumers in running water include both invertebrate and vertebrate animals. The most common invertebrates are insects. Others include snails, clams, and crayfish. Some invertebrates live on the water surface, others float suspended in the water, and still others cling to rocks on the bottom. All rely on the current to bring them food and dissolved oxygen. The invertebrates are important consumers as well as prey to the many vertebrates in running water. Vertebrate species include fish, amphibians, reptiles, birds, and mammals. However, only fish live in the water all the time. Other vertebrates spend part of their time on land.

            The movement of running water poses a challenge to aquatic organisms, which have adapted in various ways. Some organisms have hooks or threadlike filaments to anchor themselves to rocks or plants in the water. Other organisms, including fish, have fins and streamlined bodies that allow them to swim against the current.The interface between running freshwater and land is called a riparian zone. It includes the vegetation that grows along the edge of a river and the animals that consume or take shelter in the vegetation. Riparian zones are very important natural areas for several reasons:

            • They filter pollution from surface runoff before it enters a river.
            • They help keep river water clear by trapping sediments.
            • They protect river banks from erosion by running water.
            • They help regulate the temperature of river water by providing shade.

            A wetland is an area that is saturated or covered by water for at least one season of the year. Freshwater wetlands are also called swamps, marshes, or bogs. Saltwater wetlands include estuaries. Wetland vegetation must be adapted to water-logged soil, which contains little oxygen. Freshwater wetland plants include duckweed and cattails (see Figure 10, above). Some wetlands also have trees. Their roots may be partly above ground to allow gas exchange with the air. Wetlands are extremely important biomes for several reasons.

            • They store excess water from floods and runoff.
            • They absorb some of the energy of running water and help prevent erosion.
            • They remove excess nutrients from runoff before it empties into rivers or lakes.
            • They provide a unique habitat that certain communities of plants need to survive.
            • They provide a safe, lush habitat for many species of animals.

            The GAAS metagenomic tool and its estimations of viral and microbial average genome size in four major biomes

            Metagenomic studies characterize both the composition and diversity of uncultured viral and microbial communities. BLAST-based comparisons have typically been used for such analyses however, sampling biases, high percentages of unknown sequences, and the use of arbitrary thresholds to find significant similarities can decrease the accuracy and validity of estimates. Here, we present Genome relative Abundance and Average Size (GAAS), a complete software package that provides improved estimates of community composition and average genome length for metagenomes in both textual and graphical formats. GAAS implements a novel methodology to control for sampling bias via length normalization, to adjust for multiple BLAST similarities by similarity weighting, and to select significant similarities using relative alignment lengths. In benchmark tests, the GAAS method was robust to both high percentages of unknown sequences and to variations in metagenomic sequence read lengths. Re-analysis of the Sargasso Sea virome using GAAS indicated that standard methodologies for metagenomic analysis may dramatically underestimate the abundance and importance of organisms with small genomes in environmental systems. Using GAAS, we conducted a meta-analysis of microbial and viral average genome lengths in over 150 metagenomes from four biomes to determine whether genome lengths vary consistently between and within biomes, and between microbial and viral communities from the same environment. Significant differences between biomes and within aquatic sub-biomes (oceans, hypersaline systems, freshwater, and microbialites) suggested that average genome length is a fundamental property of environments driven by factors at the sub-biome level. The behavior of paired viral and microbial metagenomes from the same environment indicated that microbial and viral average genome sizes are independent of each other, but indicative of community responses to stressors and environmental conditions.

            Conflict of interest statement

            The authors have declared that no competing interests exist.


            Figure 1. Effects of length normalization and…

            Figure 1. Effects of length normalization and similarity weighting on the accuracy of GAAS estimates.

            Figure 2. Effects of metagenomic read length…

            Figure 2. Effects of metagenomic read length on average error of GAAS estimates.

            Figure 3. Re-analysis of the Sargasso Sea…

            Figure 3. Re-analysis of the Sargasso Sea viral community.

            Genome relative abundance in the Sargasso…

            Figure 4. Average genome length of viruses,…

            Figure 4. Average genome length of viruses, Bacteria and Archaea, and protists in metagenomes.

            Figure 5. Relationship between average microbial and…

            Figure 5. Relationship between average microbial and viral genome lengths in paired metagenomes.

            Figure 6. Flowchart of GAAS to calculate…

            Figure 6. Flowchart of GAAS to calculate relative abundance and average genome size.

            Watch the video: Aquatic Biomes Wetlands. Biology. Ecology (June 2022).


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