Major biomes and ecosystem types of the world.

Marine biomes:
Open ocean; seashore and estuaries; mangroves and coral reefs;

Freshwater biomes:
Rivers and streams; lakes and ponds; freshwater marsh.

Terrestrial biomes:
Desert; tundra; grassland; forest; agro-ecosystem; Urban-industrial ecosystem.

The ecosystem has been well defined by pimephalis in his write-up. To recap – “ecosystem” is the term coined by Sir Arthur Tansley (1871 – 1955) to refer to biotic and abiotic components of an area taken as a whole. The ecosystem is an open system – with energy input from the sun and other sources, and inflow of materials and organisms, as well as energy and material output and emigration of organisms.

There are various different types of ecosystem – as delineated above. An ecosystem can be very small or very large. Large ecosystems are made up of many smaller ecosystems, and are often known as “biomes”. An area between biomes, having characteristics of both, is knows as an ecotone. The term "biome" was misused in the Eden Project where it was used instead of "Bio-dome".
Thanks to Gritchka for the last two points.

These main types of ecosystem and biome have of course for the most part already received write-ups of their own. For more detailed information on all these ecosystems, see their individual nodes. This write-up is merely intended as an overview.

Marine biomes:

Open ocean biomes:

These biomes are dominated by physical characteristics – wave motion, salinity, pressure, etc. The food webs in the ocean begin with the smallest producers, and end with the largest of animals. The major oceans cover around 70% of the Earth’s surface, and consist of several different zones or ecosystem types. The ocean is divided horizontally into the photic zone (occasionally referred to as the euphotic zone) – the area of water at the surface where sunlight penetrates, and the aphotic zone – the deep water that light does not reach.

Continental shelf – the neritic zone. Fairly shallow, warm waters, usually completely in the photic zone. The bulk of undersea oil and mineral deposits are found in these ecosystems. Supplies most of the seafood harvested by humans.

The oceanic or pelagic zone. Open ocean areas that reach great depths, made up of both photic and aphotic zones.

Benthic zone – the seafloor. Supports a significant amount of sea life, including the hydrothermal vent ecosystems – hot sulphur springs at deep areas of ocean floor or on deep sea ridges. These vents support ecosystems where the food chain begins, not with photosynthetic organisms, but with chemosynthetic bacteria. Conditions in the benthic zone vary dramatically between regions.

Other marine biomes:

Intertidal zone or seashore. Physical factors such as temperature and salinity vary greatly at the oceans’ edges. Ecosystems in these regions are subject to variations of the tide – and support many organisms that can exist both partially or wholly underwater, and exposed to the air. Types of seashore vary, but usually support large numbers of shellfish, fish, and other marine life forms. Many marine mammals such as sea lions, and marine birds such as gulls, rely on the seashore to rest and mate. Intertidal zones are often fairly fragile ecosystems, and can be easily damaged by human actions.

Estuaries. An estuary is a semi-enclosed body of water such as a river mouth, where the tidal pattern allows the area to fluctuate between saline and fresh water. Estuaries support large amounts of marine life, and are often hatching grounds for shellfish and fish species. Estuaries are very fertile biomes, often due to the runoff of silt and nutrients from rivers.

Mangrove swamps. Few woody plants can tolerate the saline levels of seawater. Mangrove trees have roots that penetrate deep into the anaerobic mud, bringing oxygen and allowing for the formation of a unique ecosystem. Mangrove swamps also serve as nurseries for fish and crustaceans.

Coral reefs. These ecosystems are based on coral species, cnidarians that create a hard external skeleton of calcium carbonate. These skeletons form structures that accumulate to provide shelter, food, and a habitat for a huge variety of micro-organisms, fish species, shellfish and crustaceans. Coral reefs are among the most diverse and productive ecosystems on Earth. Reef ecosystems are very fragile, and can be destroyed very easily by pollution or water temperature variations.

Freshwater biomes:

Rivers and streams – riparian zones. Bodies of fresh water moving in one direction, and the habitat and organisms directly associated with them. Waters vary greatly in temperature, oxygenation and siltation. These ecosystems support a large range of algae, fish, amphibians and crustaceans, as well as various aquatic or semi-aquatic mammals, birds and insects. Rivers and streams can compensate fairly well for human activity such as pollution, up to a certain level, beyond which massive destruction can occur. Organisms existing in rivers are often well adapted to resisting strong current – they are often fixed, such as algae and weeds, or capable of clinging to rocks for short periods of time. The ecosystems found in rivers vary dramatically with the speed, depth, width, temperature and oxygenation of the water and the river.

Lakes and ponds. Areas of still freshwater, often geologically fairly young. These areas support a similar range of species to riparian ecosystems. Species diversity is often fairly low, and these ecosystems are quite susceptible to pollution and other human activity.

Freshwater marshes. Fairly similar to estuaries, but usually without the saline /freshwater cycle. Marshes frequently consist of grassy, occasionally wooded floodland. The marshes are often dry during parts of the year, and rely on rivers in order to be flooded in the wet season. Marshes are a rapidly disappearing ecosystem type in some areas. The Macquarie marshes in New South Wales, Australia are threatened due to the amount of water used for irrigation.

Terrestrial biomes:

Deserts. Both ‘hot’ and ‘cold’ deserts exist – the ‘hot’ desert tends to experience extreme fluctuations in temperature. ‘Cold’ deserts are only relatively low in temperature – they do not exist in areas with very low temperatures. Deserts are characterised by the fact that they receive less than 250 mm of annual precipitation, though they do occur in areas that receive more rainfall, but it is very unevenly distributed over the year. Deserts can be extremely sparsely vegetated, or have a fairly high number of plants. Desert species, both plant and animal, are distinguished by their adaptations to the desert environment – whether it be a brief life cycle, tap roots in plants, or the ability to survive without drinking water.

Tundra. The circumpolar strip of treeless plain between the polar ice cap and the tree line. Other smaller areas of arctic tundra can be found on mountains above the tree line. Tundra areas have low precipitation and low temperatures – it is the temperature rather than the lack of moisture that renders the tundra such a barren looking place. The tundra is frozen for a part of the year, and permafrost remains below the surface the year round. Various plant and animal species have adapted to exploit a niche in the cold, windy terrain.

Grasslands. Areas of grassed terrain, often with scattered trees. Mean annual precipitation is higher than that for deserts, but lower than that required by forested areas. Grasslands can be found in a range of temperature zones. Grasslands also support forbs (small broad-leaved plants) and woody plants such as shrub species. The soils generally contain more organic matter than forest soils, due to the short lived nature of grasses. The grassland ecosystems support a wide variety of grazing animals and predators. The tropical savanna is a grassland, but is often listed as a separate biome due to its higher average annual temperature.

Forests. Habitats with fairly dense tree cover. Divided into three main distinct types of forest – tropical, deciduous and coniferous.

Tropical forest. Found within 23.5° latitude of the equator, in zones where the average temperature and daylight vary only slightly throughout the year. Average annual temperature is usually around 23°C. Tropical deciduous forests are common in areas with a distinct wet and dry season, whereas tropical rainforest is found nearer the equator in areas of abundant rainfall. Tropical rainforest ecosystems are among the most species diverse of all communities, and human impact on them is a great concern.

Deciduous forest. Exist in the temperate zone (as opposed to deciduous tropical forest) where temperatures range from very cold in the winter to very hot in the summer, with moderately high rainfall throughout the year. These forests are characterised by deciduous broad-leaved trees. More open than the tropical forest, the temperate deciduous forests have relatively rich soils.

Coniferous forest. Fairly low in species diversity and with little strata complexity, coniferous forests exist in colder climates than the deciduous or tropical forests. The required rainfall zone is roughly similar to that for deciduous forests – upward of 500mm per year. Coniferous forests are frequently man-made or subject to logging.

Agroecosystems. Often monocultures, planted by mankind for agricultural purposes. Extremely low in species diversity and often low in genetic diversity within species. They also have a far more linear nutrient and energy flow than do natural ecosystems – far more of the nutrients, materials and energy are imported and exported from the ecosystem. Agroecosystems are often susceptible to disease or pests, however human intervention seeks to prevent destruction by these agents. Agroecosystems have been established in most temperature/rainfall zones on Earth.

Urban-industrial ecosystems. Cities and industrial areas: the concrete jungles. Also have extremely linear nutrient and energy flow, as well as being established in all temperature/rainfall zones. They possess fairly low species diversity, and are difficult to discuss in similar terms to the other biomes of the world.

The end. Congratulations to anyone who hung around for all that.

“Ecology and Our Endangered Life-Support Systems”, by Eugene P. Odum, published Sinauer Associates 1993,
and the gospel of biology students everywhere: “Biology” Third edition, by Neil A. Campbell, published Benjamin/Cummings 1993.

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