Aquatic Biomes Aquatic biomes are characterized by

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Online exhibits : The world’s biomes

The aquatic biome

Coral reef diversity


Water is the common link among the five biomes and it makes up the largest part of the biosphere, covering nearly 75% of the Earth’s surface. Aquatic regions house numerous species of plants and animals, both large and small. In fact, this is where life began billions of years ago when amino acids first started to come together. Without water, most life forms would be unable to sustain themselves and the Earth would be a barren, desert-like place. Although water temperatures can vary widely, aquatic areas tend to be more humid and the air temperature on the cooler side.

The aquatic biome can be broken down into two basic regions, freshwater and marine:


  • Ponds and lakes
  • Streams and rivers
  • Wetlands


  • Oceans
  • Coral reefs
  • Estuaries

The aquatic biome can be broken down into two basic regions, freshwater (ponds and rivers) and marine (oceans and estuaries).

Freshwater regions

Freshwater is defined as having a low salt concentration — usually less than 1%. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration (i.e., ocean). There are different types of freshwater regions: ponds and lakes, streams and rivers, and wetlands. The following sections describe the characteristics of these three freshwater zones.

Ponds and lakes

Ponds and lakes photos

These regions range in size from just a few square meters to thousands of square kilometers. Scattered throughout the earth, several are remnants from the Pleistocene glaciation. Many ponds are seasonal, lasting just a couple of months (such as sessile pools) while lakes may exist for hundreds of years or more. Ponds and lakes may have limited species diversity since they are often isolated from one another and from other water sources like rivers and oceans. Lakes and ponds are divided into three different “zones” which are usually determined by depth and distance from the shoreline.

The topmost zone near the shore of a lake or pond is the littoral zone. This zone is the warmest since it is shallow and can absorb more of the Sun’s heat. It sustains a fairly diverse community, which can include several species of algae (like diatoms), rooted and floating aquatic plants, grazing snails, clams, insects, crustaceans, fishes, and amphibians. In the case of the insects, such as dragonflies and midges, only the egg and larvae stages are found in this zone. The vegetation and animals living in the littoral zone are food for other creatures such as turtles, snakes, and ducks.

The near-surface open water surrounded by the littoral zone is the limnetic zone. The limnetic zone is well-lighted (like the littoral zone) and is dominated by plankton, both phytoplankton and zooplankton. Plankton are small organisms that play a crucial role in the food chain. Without aquatic plankton, there would be few living organisms in the world, and certainly no humans. A variety of freshwater fish also occupy this zone.

Plankton have short life spans — when they die, they fall into the deep-water part of the lake/pond, the profundal zone. This zone is much colder and denser than the other two. Little light penetrates all the way through the limnetic zone into the profundal zone. The fauna are heterotrophs, meaning that they eat dead organisms and use oxygen for cellular respiration.

Temperature varies in ponds and lakes seasonally. During the summer, the temperature can range from 4° C near the bottom to 22° C at the top. During the winter, the temperature at the bottom can be 4° C while the top is 0° C (ice). In between the two layers, there is a narrow zone called the thermocline where the temperature of the water changes rapidly. During the spring and fall seasons, there is a mixing of the top and bottom layers, usually due to winds, which results in a uniform water temperature of around 4° C. This mixing also circulates oxygen throughout the lake. Of course there are many lakes and ponds that do not freeze during the winter, thus the top layer would be a little warmer.

Streams and rivers

Streams and rivers photos

These are bodies of flowing water moving in one direction. Streams and rivers can be found everywhere — they get their starts at headwaters, which may be springs, snowmelt or even lakes, and then travel all the way to their mouths, usually another water channel or the ocean. The characteristics of a river or stream change during the journey from the source to the mouth. The temperature is cooler at the source than it is at the mouth. The water is also clearer, has higher oxygen levels, and freshwater fish such as trout and heterotrophs can be found there. Towards the middle part of the stream/river, the width increases, as does species diversity — numerous aquatic green plants and algae can be found. Toward the mouth of the river/stream, the water becomes murky from all the sediments that it has picked up upstream, decreasing the amount of light that can penetrate through the water. Since there is less light, there is less diversity of flora, and because of the lower oxygen levels, fish that require less oxygen, such as catfish and carp, can be found.


Wetlands photos

Wetlands are areas of standing water that support aquatic plants. Marshes, swamps, and bogs are all considered wetlands. Plant species adapted to the very moist and humid conditions are called hydrophytes. These include pond lilies, cattails, sedges, tamarack, and black spruce. Marsh flora also include such species as cypress and gum. Wetlands have the highest species diversity of all ecosystems. Many species of amphibians, reptiles, birds (such as ducks and waders), and furbearers can be found in the wetlands. Wetlands are not considered freshwater ecosystems as there are some, such as salt marshes, that have high salt concentrations — these support different species of animals, such as shrimp, shellfish, and various grasses.

Visit our gallery of wetlands images , which illustrate the amazing diversity of wetland ecosystems.

Marine regions

Marine regions cover about three-fourths of the Earth’s surface and include oceans, coral reefs, and estuaries. Marine algae supply much of the world’s oxygen supply and take in a huge amount of atmospheric carbon dioxide. The evaporation of the seawater provides rainwater for the land.


Ocean photos

The largest of all the ecosystems, oceans are very large bodies of water that dominate the Earth’s surface. Like ponds and lakes, the ocean regions are separated into separate zones: intertidal, pelagic, abyssal, and benthic. All four zones have a great diversity of species. Some say that the ocean contains the richest diversity of species even though it contains fewer species than there are on land.

The intertidal zone is where the ocean meets the land — sometimes it is submerged and at other times exposed, as waves and tides come in and out. Because of this, the communities are constantly changing. On rocky coasts, the zone is stratified vertically. Where only the highest tides reach, there are only a few species of algae and mollusks. In those areas usually submerged during high tide, there is a more diverse array of algae and small animals, such as herbivorous snails, crabs, sea stars, and small fishes. At the bottom of the intertidal zone, which is only exposed during the lowest tides, many invertebrates, fishes, and seaweed can be found. The intertidal zone on sandier shores is not as stratified as in the rocky areas. Waves keep mud and sand constantly moving, thus very few algae and plants can establish themselves — the fauna include worms, clams, predatory crustaceans, crabs, and shorebirds.

The pelagic zone includes those waters further from the land, basically the open ocean. The pelagic zone is generally cold though it is hard to give a general temperature range since, just like ponds and lakes, there is thermal stratification with a constant mixing of warm and cold ocean currents. The flora in the pelagic zone include surface seaweeds. The fauna include many species of fish and some mammals, such as whales and dolphins. Many feed on the abundant plankton.

The benthic zone is the area below the pelagic zone, but does not include the very deepest parts of the ocean (see abyssal zone below). The bottom of the zone consists of sand, slit, and/or dead organisms. Here temperature decreases as depth increases toward the abyssal zone, since light cannot penetrate through the deeper water. Flora are represented primarily by seaweed while the fauna, since it is very nutrient-rich, include all sorts of bacteria, fungi, sponges, sea anemones, worms, sea stars, and fishes.

The deep ocean is the abyssal zone. The water in this region is very cold (around 3° C), highly pressured, high in oxygen content, but low in nutritional content. The abyssal zone supports many species of invertebrates and fishes. Mid-ocean ridges (spreading zones between tectonic plates), often with hydrothermal vents, are found in the abyssal zones along the ocean floors. Chemosynthetic bacteria thrive near these vents because of the large amounts of hydrogen sulfide and other minerals they emit. These bacteria are thus the start of the food web as they are eaten by invertebrates and fishes.

Coral reefs

Coral reef photos

Coral reefs are widely distributed in warm shallow waters. They can be found as barriers along continents (e.g., the Great Barrier Reef off Australia), fringing islands, and atolls. Naturally, the dominant organisms in coral reefs are corals. Corals are interesting since they consist of both algae (zooanthellae) and tissues of animal polyp. Since reef waters tend to be nutritionally poor, corals obtain nutrients through the algae via photosynthesis and also by extending tentacles to obtain plankton from the water. Besides corals, the fauna include several species of microorganisms, invertebrates, fishes, sea urchins, octopuses, and sea stars.


Estuary photos

Estuaries are areas where freshwater streams or rivers merge with the ocean. This mixing of waters with such different salt concentrations creates a very interesting and unique ecosystem. Microflora like algae, and macroflora, such as seaweeds, marsh grasses, and mangrove trees (only in the tropics), can be found here. Estuaries support a diverse fauna, including a variety of worms, oysters, crabs, and waterfowl.

Top photo of reef fish and coral at Eniwetok by Dr. James P. McVey, NOAA Sea Grant Program. Ponds & Lakes photos, from left: Manzanita Lake, CA, by Glenn and Martha Vargas © 2004 California Academy of Sciences; Idaho pond by David K. Smith, UCMP; Great Blue Heron by Gerald and Buff Corsi © 2001 California Academy of Sciences; Paranagat Lake, NV, by Glenn and Martha Vargas © 2004 California Academy of Sciences. Streams & Rivers photos, from left: McArthur-Burney Falls State Park, CA, by Dr. G Dallas and Margaret Hanna © 1999 California Academy of Sciences; Trout by Susan Middleton © 2003 California Academy of SciencesGreen River, UT, by Lorraine Elrod © 2000 California Academy of Sciences; Brooks River, AK, by Dr. Robert Thomas and Margaret Orr © 2004 California Academy of Sciences. Wetlands photos, from left: Pescadero Marsh, CA, by Dr. Robert Thomas and Margaret Orr © 1999 California Academy of Sciences; Umpqua Dunes marsh, OR, by David K. Smith, UCMP; Trees and bogs on Esther Island, AK, by Gerald and Buff Corsi © 2005 California Academy of Sciences. Oceans photos, from left: Mussels, worms, and spider crab, Gulf of Mexico, by I. MacDonald, OAR/National Undersea Research Program (NURP) / Texas A&M University; Brain coral and sea fan, Florida Keys National Marine Sanctuary, by Stephen Cook, National Oceanic and Atmospheric Administration / Department of Commerce; Amberjack by A. Hulbert, OAR/National Undersea Research Program (NURP) / University of North Carolina at Wilmington. Coral Reef photos, from left: Gulf of Aqaba reef, Red Sea, by Mohammed Al Momany, National Oceanic and Atmospheric Administration / Department of Commerce; Fanning Island reef by Dr. James P. McVey, NOAA Sea Grant Program; Florida Keys National Marine Sanctuary by Mike White, National Oceanic and Atmospheric Administration / Department of Commerce. Estuaries photos, from left: Mangrove roots, FL, OAR/National Undersea Research Program (NURP); View of wetlands and tidal streams south of Charleston, SC, and Salt marsh near Georgetown, SC, National Oceanic and Atmospheric Administration / Department of Commerce.

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Biology 101: The Basics

Aquatic Biomes

Aquatic biomes are defined as biomes that are located in water, rather than on land. A biome is an ecological community with a specific climate and certain plants and animals that live in it. There are two types of biomes: terrestrial  and aquatic. You can click on the link to learn more about terrestrial biomes. 

Image of an aquatic biome

Characterizing Aquatic Biomes


Image of salt in a glass bottle set on dark table background

Aquatic biomes are split up into two categories depending on how much salt is in the water.

There are many features used to characterize aquatic biomes. One important factor is the type of water in the biome. Water on Earth can be divided into two categories: freshwater and saltwater.

Some aquatic biomes have only freshwater, some have only saltwater, and some have a mixture of both. On Earth, most of the water is saltwater. Freshwater biomes are especially important for humans because we need freshwater to drink. 

Aquatic biomes are also characterized by their location, the temperature of the water, and the types of plants and animals that live in them.


Types of Aquatic Biomes 

Listed below are nine major types of aquatic biomes and a short description of each. Some of these biomes are broad categories that include other biomes. You can click on each link to learn more about the different types of biomes. 
Freshwater Biome : Freshwater biomes are a major category of aquatic biomes and include any biome with water that is not saltwater. There are three types of freshwater biomes: lakes and ponds, rivers and streams, and wetlands. Freshwater biomes are found in places all over the world. 
Lakes and Ponds Biome : Lakes and ponds are types of freshwater biomes. They are not attached to any other water sources and don’t have moving water. 
Rivers and Streams Biome : Rivers and streams are types of freshwater biomes. Unlike lakes and ponds, rivers and streams have moving water and are connected to other sources of water
Wetlands Biome : Wetlands are biomes in which the land is completely covered by water. Some wetlands are only covered with water during certain times of the year. In a wetland, the water can either be freshwater or saltwater.


Image of the Map of the Earth laid out

Looking at a map you can see that most of the Earth is covered by aquatic biomes!

Marine Biome : The marine biome is a large aquatic biome that includes all of the Earth’s oceans and other bodies of water, such as bays and estuaries. The water in a marine biome is saltwater and has an average temperature of 4 °C.
Oceans Biome Oceans are a type of marine biome. There are five ocean biomes on Earth: Atlantic, Pacific, Indian, Southern, and Arctic. The oceans have an average temperature of 4 °C and are saltwater. 
Coral Reefs Biome : Coral reefs are a type of marine biome located in water that is warm and shallow. Coral reefs are known for their beautiful corals and many types of fish and other animals that live in them. 
Estuaries Biome : Estuaries are a type of marine biome that exist where a freshwater area mixes with a saltwater area. For example, the place where a freshwater river meets the ocean is an estuary. The water in an estuary is a mixture of freshwater and saltwater. 
Polar Ice Biome : The polar ice biome is found far from the equator, at the Earth’s poles. This aquatic biome is unique because the water is frozen. The polar ice biome is very cold, with temperatures below 0 °C.  
Written by: Leah Tolby
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