AQUATIC BIOMES: CHARACTERISTICS, TYPES, FLORA, FAUNA, EXAMPLES - BIOLOGY - 2025

The aquatic biomes are those areas of the planet whose main medium is water, which are adapted to living organisms that live there. These biomes can be marine or freshwater.

In marine biomes, water is characterized by having a relatively high salt content while freshwater biomes have little dissolved salts. These biomes span 5 oceans with 57 seas, and freshwater biomes include an extensive system of rivers, lakes, lagoons, swamps, and other wetlands.

Aquatic biome. Source: Fernando Flores

Water as a habitat for life has different characteristics from the terrestrial environment, derived from its higher density, variable turbidity and less thermal oscillation. On the other hand, the light factor experiences an important vertical variation as a function of the turbidity of the water and its depth.

Both macroscopic and microscopic algae dominate marine biomes and aquatic angiosperms are also found in coastal areas. While in freshwater biomes there is a greater abundance of both floating and submerged angiosperms.

The fauna of aquatic biomes includes fish, crustaceans, bivalves, mollusks, aquatic mammals, and aquatic birds.

Characteristics of aquatic biomes

Aquatic biomes differ fundamentally in terms of salt content between marine and freshwater biomes. In these biomes, the medium or substrate where life develops is water, which gives it particular characteristics.

Water

It is a liquid substance composed of oxygen and hydrogen and is essential for life. In fact, life on Earth arose in the primitive ocean more than 4.5 billion years ago.

Water covers about 71% of the earth's surface, mostly contained in the oceans. It fulfills a permanent cycle, called the water cycle, based on its evaporation, precipitation and runoff or displacement towards the sea.

Properties

Pure water is colorless, odorless and tasteless, but in aquatic habitats water has organic and mineral substances that give it odors, flavors and colors. These dissolved substances come from its movement through the earth, given its solvent power, and they give it different degrees of turbidity.

The turbidity of the water affects the penetration of sunlight into the water column, which has implications for life. This due to light is required for photosynthesis which is the basis of most food chains.

Salinity and density

The water drags and dissolves mineral salts as it continues its course towards the ocean and that is why the concentration of salts in them is so high. The concentration of salts in addition to representing an important environmental condition to which life must adapt, affects the density of water. The higher the salt content, the denser the water.

Dissolved gases

Water maintains a permanent gaseous exchange with the atmosphere, which is why it presents dissolved gases such as oxygen and CO2.

Oxygen is vital for the life of aerobic organisms and those that live in water have adapted to obtain it from it. Mammals that have adapted to marine life must frequently emerge to obtain oxygen directly from the air.

Temperature

This substance is less susceptible to drastic changes in temperature than the air environment and it remains liquid between 0ºC and 100ºC. In aquatic biomes, temperature varies with latitude and altitude, as well as with the depth of the water.

Light

Liquid water in its pure state absorbs little light, but when there are particles in suspension, the penetration of sunlight is difficult. The cloudier and deeper the water column, the less light penetrates.

This conditions the different habitats that occur in the vertical dimension of an aquatic biome.

Currents

Gravity and temperature differences generate water currents of greater or lesser magnitude.

Rivers

In rivers, the water moves due to gravity due to a difference in the slope of the terrain, forming the course of the river. It is defined by the degree of slope, the geological structure and the relief of the terrain through which it runs.

Rivers make up the so-called lotic ecosystems, characterized by the movement of water in one direction. The speed of the current generated is defined by the slope, water flow and area of ​​the river channel.

Lakes, lagoons and swamps

The lakes are wide depressions where water from rivers and rain accumulate. They are lentic ecosystems, that is, closed bodies of water, without the water flowing in a defined direction.

In lakes, winds produce waves by pushing water towards their shores. When they are large and deep, the differences in temperature between the surface and deep water bodies also generate currents.

Ocean currents and tides

The oceans of the planet are interconnected forming a gigantic body of water in which the temperature regime produces a system of currents. These currents can be deep or shallow.

Deep currents are generated by differences in water temperature and density. In the case of surface currents, they are produced by the force of the winds and the inertia of the earth's rotation.

These currents follow regular cycles with a defined direction, horizontally and vertically. The latter generates the phenomenon of cold water upwelling, that is, the rise of cold deep waters to the surface.

On the other hand, the gravity of the Sun, Moon and Earth generate the phenomenon of tides, which are cyclical rises and falls of the sea level. These variations in sea level form what is called the intertidal zone, which represents an important ecological niche.

Types of aquatic biomes

Coral reef. Source: US Fish & Wildlife Service - Pacific Region's Photo credit: Jim Maragos / US Fish and Wildlife Service

There are two main types of aquatic biomes, defined by physical and chemical characteristics, which in turn condition the flora and fauna that inhabit them. These are the marine and freshwater biomes, as well as transitional ecosystems such as estuaries and deltas.

Estuaries occur in wide-section rivers at their mouths when seawater penetrates, forming a brackish water ecosystem. For their part, deltas originate when a large river divides into multiple channels at its mouth, forming an extensive triangular area.

Marine biomes

These encompass the different environments that are generated in the planet's oceans, characterized mainly by their high salt content (greater than 1.05%). They have an average depth of 4,000 m, the maximum depth being reached in the Las Marianas Trench (11,033 m).

Temperature and salinity

The temperature of the seas varies from -2 ºC in the polar zones to 36 ºC in the tropics. Vertically, the temperature remains constant in the first 400 m, to drop drastically later to 3 and 0 ºC.

About 80% of the dissolved salts in the oceans is sodium chloride, that is, common salt.

Marine life zones

The conformation of the oceans determines the existence of various zones that offer different environmental conditions. In a horizontal direction, there is the littoral or neritic zone, while when moving away from the coast there is the oceanic or pelagic zone.

While in the vertical sense a series of zones are also determined depending on the depth.

Additionally, as the depth increases, the illumination decreases and a euphotic zone (sufficient light), a dysphotic (little illumination) and an aphotic (darkness) appear.

Diversity of biomes and ecosystems

Posidonia marine meadow. Source: albert kok

The oceans are not a single biome, so their extension and variability determine the existence of several biomes with multiple ecosystems. Polar seas offer very different environmental conditions for life than tropical seas.

For example, the cold waters produced by the upwelling in the Humboldt Current are richer in nutrients than the warm waters of the tropics. This explains the great fishing wealth that this current generates on the coasts of the Pacific Ocean in southern South America.

However, the higher temperature and solar radiation in the tropics offer suitable conditions for the development of other ecosystems. These include coral reefs, underwater grasslands that are associated with a land-sea transition biome, such as the mangrove swamp.

In addition to latitudinal variations, coastal zones host totally different ecosystems than open ocean areas.

Other factors such as the mineral contributions from underwater vents at great depths, also constitute a particular biome. In these areas, more than 2,000 m deep, sunlight does not reach, so primary production depends on archaea that process sulfur.

From these bacteria-like organisms, ecosystems rich in life have developed, like oases in the middle of the desert on the seabed.

Freshwater biomes

Freshwater biomes include all natural continental and island water bodies with a salt content of less than 1.05%. This includes rivers, ponds, lakes, and swamps.

An exception to this level of salinity are salt water lakes, such as the Caspian Sea, the Aral Sea, Lake Baljash and the Chiquita Sea.

Among these biomes is a network of rivers, with smaller rivers tributaries to larger ones that drain until they flow into lakes or finally into the sea. The great rivers run through different areas from their source to their mouth, generating a diversity of ecosystems.

The great tropical rivers

Amazon River. Source: Neil Palmer / CIAT

These include the Amazon and Orinoco in South America, or the Congo in Africa, and they are highly biodiverse freshwater biomes. They have a complex ecological dynamic in relation to the tropical rainforests that they cross.

The Amazon runs 6,400 kilometers from its source in the Andes Mountains to its mouth in the Atlantic Ocean. This river contains about a fifth of the fresh water in liquid form on the planet.

Its basin (set of tributary rivers) covers 7.05 million km2 and periodically the river overflows invading the Amazon jungle. This establishes a transitional ecosystem between the terrestrial jungle biome and the river.

In this river there are more than 3,000 species of fish, as well as various species of turtles and alligators. Likewise, there are aquatic mammals such as the river dolphin and the manatee.

Flora

- Marine flora

Phytoplankton

Phytoplankton diversity. Taken and edited from: Prof. Gordon T. Taylor, Stony Brook University, via Wikimedia Commons.

It is a set of microscopic organisms with the capacity to carry out photosynthesis. These are not vegetables, although they have traditionally been studied as algae, they are actually bacteria (cyanobacteria) and protists.

The dominant group within phytoplankton are diatoms, of which there are about 20,000 species. Phytoplankton is the basis of almost all marine food chains, as well as the main source of oxygen on the planet.

Arches

A particular group of living things are archaea, which are microscopic prokaryotic bacteria-like organisms. These are autotrophs, obtaining their food by chemosynthesis (from inorganic substances such as sulfur they produce usable chemical energy).

Archaea are the base of the food chain in ecosystems that are generated around ocean vents.

Algae

Fucus spiralis alga in Tenerife (Spain). Source: Juan Félix García Reyes

They are unicellular and multicellular photosynthesizing organisms that present different types of pigments such as green, brown and red. There are more than 30,000 species of algae, from microscopic to 100 meters in length.

Algae develop either as part of the plankton, that is, floating, or as part of the benthos (attached to the seabed or corals). Because they require sunlight to photosynthesize, these organisms grow shallow.

In the North Atlantic there is the so-called Sargasso Sea, which consists of an area of ​​more than 3 million km2. This area is so named because it is covered with massive floating populations of the Sargassum alga along with other species and plankton.

Sometimes, environmental alterations generate the proliferation of microalgae forming the so-called red tide or harmful algal blooms. Although the term red tide has become widespread, it really is not always this color. These algae produce toxins that by bioaccumulation cause problems for marine fauna.

Angiosperm herbs

Underwater grass meadows belonging to monocotyledonous angiosperms develop in shallow marine areas. These are grouped into 4 plant families that are Posidoniaceae, Cymodoceaceae, Zosteraceae and Hydrocharitaceae.

For example, associated with mangroves in the American tropics are the grasslands of the Alismataceae Thalassia testudinum. This grass is known as turtle grass, because turtles eat it, just like manatees do.

In the waters of the Mediterranean, species such as Posidonia oceanica and Cymodocea nodosa inhabit.

Flora

Freshwater algae to floating, rooted and submerged angiosperm plants inhabit freshwater biomes. On the other hand, there are many species of plants, even trees, adapted to swamp conditions or long periods of flooding.

For example, trees such as Cecropia latiloba and Macrolobium acaciifolium are found in the flooded forests of the Amazon or igapós.

Aquatic angiosperms

Victoria amazonica. Source: Cbaile19

There are several families of angiosperm plants that include freshwater species, both floating, deep-rooted and emerging and submerged. From the smallest angiosperm that exists, the floating duckweed (Lemna spp.) To the Amazon water lily (Victoria amazonica).

Families such as Potamogetonaceae, Hydrocharitaceae, Alismataceae, Juncaceae, Nymphaeaceae and Araceae among others, include plants from freshwater ecosystems. Additionally, the Droseraceae family of insectivorous plants includes the aquatic species Aldrovanda vesiculosa that captures small animals such as the water flea.

Fauna

- Marine fauna

Marine fauna can be part of plankton (floating with the current), benthos or nekton (swimming freely).

Zooplankton

Northern Krill (Meganyctiphanes norvegica). Source: Øystein Paulsen

Forming part of the plankton (communities of floating microscopic organisms), is the zooplankton. They are microscopic beings that float dragged by ocean currents, including protozoa and larvae of larger animals (sponges, sea urchins, mollusks, crustaceans).

However, 70% of zooplankton is made up of copepods, which are crustaceans. An important component of zooplankton is the microscopic crustacean called krill, both the northern (Meganyctiphanes norvegica) and the Antarctic (Euphausia superba).

jellyfish

Jellyfish Aurelia aurita, an organism that inhabits the pelagic zone. Taken and edited from: I, Luc Viatour.

There are also other animals that are swept away by ocean currents, such as jellyfish.

Benthos

Community of benthos at an abyssal depth in the islands of Hawaii. Taken and edited from NOAA Photo Library, via Wikimedia Commons.

Adhered to the substrate we find a great diversity of animal groups, which includes anemones, sponges, sea urchins, tube worms and corals. Additionally, starfish, mollusks and bivalves move along the bottom.

Necton

Nekton organism, Whale Shark, Rhincodon typus. Taken and edited from: Tilonaut, via Wikimedia Commons.

In the seas there is an enormous diversity of fish species, both bone and cartilaginous. Among the first, which have calcareous skeletons, we find from the small sardine to the sunfish (Mola mola) that reaches 1,000 kilos in weight.

Among those that have cartilage instead of bones, are sharks (Selacimorphs), sawfish and rays (Batoids).

Likewise, there are cephalopod mollusks such as octopus, squid, cuttlefish and nautilus. On the other hand, there are marine mammals such as whales, killer whales and dolphins, as well as manatees, seals, sea lions and walruses.

Reptiles are also represented by sea turtles and even saltwater crocodiles.

- Fauna

Fishes

About 41.24% of known fish species inhabit freshwater bodies. The great diversity is due to the geographic isolation that exists between the different basins.

Reptiles

Various species of crocodiles and alligators are found in freshwater biomes as well as amphibian snakes such as the anaconda. Various species of river turtles are also common.

Amphibians

Freshwater biomes are home to amphibians and species of frogs, toads, and salamanders abound.

Mammals

Manatee (Trichechus sp.). Source: Chris Muenzer

In the tropical rivers of America there are different species of dolphins as well as the manatee and the otter. In rivers and lagoons also inhabits the chigüire or capybara, a giant amphibian rodent.

In the case of the rivers and lakes of North America, it is possible to get the beaver that builds dikes and the hippopotamus inhabits the African rivers.

Acuatic birds

There are numerous species of birds adapted to life in aquatic biomes, which feed on the organisms that live there. Among these are wading birds, named for their long legs that allow them to wade through shallow waters.

These birds include the flamingo (Phoenicopterus spp.), The great bustard (Otis tarifa) and the cranes (Gruidae).

Insects

3% of insect species are aquatic, that is, they spend all or part of their life cycle in water. These include the water beetle (Gyrinus natator) in fresh water and the alkaline fly (Ephydra hians) in salt water.

Aquatic biomes of the world

- America

Coral formations abound on the coasts of tropical and subtropical America, associated with seagrass beds, especially in the Caribbean Sea. While to the north in the United States and Canada there are extensive areas of lakes in temperate to cold climates.

Similarly, in America there are some of the largest rivers in the world, such as the Amazon River, the Orinoco, the La Plata River and the Mississippi.

Cold sea and warm sea

Two very different biomes are connected on the Pacific coast of South America, the cold sea to the south and the warm sea to the north. The first determined by the Humboldt Current and the second by the Equatorial Countercurrent.

Flora and fauna

The flora and fauna present in these biomes is rich and varied, including tropical, temperate and cold areas. Finding, for example, the manatee from Florida (USA) to South America and to the south, sea lions and seals are located.

The Amazon River is home to alligators, anacondas and large fish such as the arapaima (Arapaima gigas), the second largest fish in the world. Likewise, in this river there are abundant fish that are used in aquariums, such as the scalar or angelfish (Pterophyllum scalare).

- Africa

The coasts of this continent are washed by the Atlantic Ocean to the west, the Indian Ocean to the east, the Mediterranean Sea to the north and the Antarctic Ocean to the south. Therefore, the marine biomes found here are very varied, from tropical waters to cold waters in the south and temperate waters in the north.

Map and route of the Nile River through Africa. Source: River Nile map.svg: Hel-hama (talkcontribs) derivative work: Rowanwindwhistler

On the other hand, Africa has large rivers such as the Congo and the Nile, in addition to the Great Lakes of Africa, distributed throughout the Rift Valley. Among them Lake Victoria, the second largest freshwater lake in the world.

- Europe

Ebro River. Source: AerisPixel

The European continent has temperate and cold marine biomes, having coasts with the Arctic Ocean to the north, the Atlantic to the west and the Mediterranean Sea to the south. In the same way, there are a series of relevant rivers in that continent such as the Volga, the Danube, the Rhine, the Seine and the Ebro.

The Danube River

Danube river

Various species of fish are found in the Danube, some endemic such as Danube salmon (Hucho hucho). In this basin you can also find the European mudfish (Umbra krameri), used as an aquarium fish.

- Asia

This continent has coasts in the Arctic Ocean to the north, the Pacific to the east and southeast, and the Indian Ocean to the south. In addition, there are several hydrographic basins that cover from cold to tropical climate and among the most important rivers are the Ganges, the Yangtze, the Euphrates and the Indus.

Lake ecosystem

In Asia there are various lake ecosystems, the largest of which is the Tam Giang-Cau Hai lagoon in Vietnam.

The Coral Triangle

In Southeast Asia there is an extensive system of coral reefs called the Coral Triangle. This ecosystem includes the greatest diversity of corals on the planet (500 species) and more than 2,000 species of fish.

- Oceania

The most characteristic biome of this part of the planet is the Great Barrier Reef of Australia. Although this coral reef only represents 0.1% of the oceanic surface, it is the habitat of 8% of the world's fish species.

References

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