The aquatic biome can be broken down into two basic areas

• freshwater (i.e, ponds and rivers)
• marine (i.e, oceans and estuaries)

Freshwater Regions

• Ponds and Lakes
• These regions range in size of just a few square meters to thousands of square kilometers.



• many of the first lakes evolved during the Pleistocene Ice Age



• Many ponds are seasonal, just lasting a couple of months, such as sessile pools, while lakes last many years.



• There is not that much diversity in species since ponds and lakes 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 its distance from the shoreline.
• The top most zone near the shores of the lake or pond is the littoral zone.
• This shallow zone is the warmest since it is the area that light hits contains flora such as rooted and floating aquatic plants, and contains a very diverse community, which can include several species of algae, 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 fauna includes such species as turtles, snakes, and ducks feed on the vegetation and other animals in the littoral zone.



• Next to the littoral zone is the limnetic zone,
• open water away from the shore.
• This zone like the littoral zone is also well-lighted, that is why it is dominated by plankton, such as phytoplankton and zooplankton.
• Plankton are small organisms that can feed and reproduce on their own and serve as food for small chains. Without plankton in the water, there would not be any living organisms in the world, including humans. A variety of freshwater fish also occupy this zone.



• The small plankton do not live for a long time. 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 zones.
• This zone is colder since not too much light penetrates all the way through the limnetic zone into the profundal zone.



• Fauna in this zone are heterotrophs, meaning that they eat dead organisms, and use oxygen for cellular respiration.



• Temperature varies in ponds and lakes during the different seasons.
• During the summer, the temperature can range from 4C near the bottom to 22C at the top.



• During the winter, the temperature at the bottom would be 4C while the top would be 0 C (ice).



• In between the two layers, there is a narrow zone called 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 cause a uniform temperature of around 4C.
• This mixing also allows the oxygen level to be the same through the lake. Of course this is only a generalization since there are many lakes and ponds that do not freeze during the winter, thus the top layer would be a little warmer.



• Shallow lakes tend to be more productive



• Oligotrophic vs. eutrophic lakes





• Streams and Rivers
• Bodies of flowing water moving in one direction (relationship to plankton?)



• They start off at headwaters, such as springs, snowmelt or even lakes, then travel all the way to a mouth, which is usually a channel or the ocean



• The characteristics of a river or stream changes going from the source to the mouth.
• The temperature is cooler at the source than it is at the mouth.



• At the source the water is also clearer, has high oxygen levels and freshwater fish such as trout along with heterotrophs can be found there.



• Towards the middle part of the stream/river, the width increases, and less shaded. Also the greatest species diversity along streams and rivers, including numerous aquatic green plants and algae, can be found around this area.



• Towards the mouth of the river/stream, the water becomes murky from all the sediments that it has collected from the upper parts, thus 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 do not less as much oxygen, such as catfish and carp, can be found.



• Wetlands
• Wetlands are areas covered with standing water that supports aquatic plants.



• Marshes, swamps, and bogs are all considered wetlands.



• The plant species that are found in wetlands have been adapted to the very moist and humid conditions are called hydrophytes. (pond lillies, cattails, sedges, tamarack, and black spruce)



• In terms of species diversity, the wetlands are the most abundant of all ecosystems.
• Many species of amphibians, reptiles, birds, such as ducks and waders, and furbearers can be found in the wetlands.



• Not all wetlands belong to freshwater ecosystems. There are other wetlands, such as salt marshes, that have a high concentration of salt, and thus house different species of animals, such as shrimp and shellfish, and plants, such as grass.

Marine Regions

• Oceans
• The largest of all the ecosystems



• Oceans are very large body of water that dominants 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 less species than there are on land.
• The intertidal zone
• where the ocean meets the land, like the shore or rocky areas, thus it is submerged sometimes, and exposed at other times as waves come in and out of the area.



• The communities are constantly changing.



• In the rocky areas, the zone is stratified vertically. On the highest part where only the highest tides reach, there are only a few species of algae and mollusks.



• In the part where it is usually submerged during high tide, there is more diverse array of algae and small animals, such as herbivorus snails, crabs, sea stars, and small fishes.



• The bottom of the intertidal zone, which is only exposed during the lowest tides, houses many invertebrates and fishes, along with a lot of seaweed.



• The intertidal zone on shores are not as stratified as the rocky areas.
• Waves cause mud and sand to be constantly moving, thus very few algae and plants can establish themselves there. The fauna there includes worms, clams, predatory crustaceans, crabs, and shorebirds.



• The pelagic zone
• All the water that is not near the shore or land, basically the open ocean.
• In the open oceans fish, whales and crustaceans swim actively to pursue food, these animals are called pelagic
• floating algae = phytoplankton
• since sunlight cannot penetrate to great depths the phytoplankton are located in the upper regions of the oceans
• euphotic zone



• Zooplankton
• located at greater depths than phytoplankton but migrate upwards at night to feed



• Generally cold though it is hard to give a general temperature range since, just like ponds and lakes, there is thermal stratification, and there is always mixing of warm and cold ocean currents.



• The flora in the pelagic zone include seaweed on the surface of the water. The fauna includes many species of fish and some mammals, such as whales and dolphins. They feed on the plankton that are found all over the water.

• The abyssal zone
• very cold (around 3 C), highly pressured, high in oxygen content, but low in nutritional content.



• The abyssal zone houses many species of invertebrates and fishes.



• Also in this zone are mid-ocean ridges, which contains hydrothermal vents.
• These ridges, according to theory, were lines of former contact between continents. Since large amounts of hydrogen sulfide and other minerals are emitted from these ridges, chemosynthetic bacteria dominant the area in terms of plankton. These bacteria are thus the start of the food web as they are eaten by invertebrates and fishes.



• The benthic zone
• below the pelagic zone, but not at the deepest parts of the ocean, as where the abyssal zone is located.



• The bottom of the zone consists of sand, slit, wastes, and/or dead organisms.



• temperature decreases as the depth increases towards the abyssal zone, since light cannot penetrate through the deeper water.



• The flora in this zone only consists of seaweed while the fauna, since it is very nutrient rich, includes all sorts of bacteria, fungi, sponges, sea anemones, worms, sea stars, and fishes



• Coral Reefs
• Widely distributed in warm shallow waters.
• Found as barriers along continents (i.e., the Great Barrier Reef off Australia), fringing islands, and atolls



• The dominating species in coral reefs is of course coral.
• Coral is quite an interesting species since it is consists of both algae (zooanthellae) and tissues of animal polyp.
• Since the water in the area is generally nutritionally poor the coral obtains nutrients through the algae via photosynthesis and also by extending tentacles to obtain plankton from the water. Besides the coral, the fauna includes several species of microorganisms, invertebrates, fishes, sea urchins, octopuses, and sea stars.



• Estuaries
• Areas where freshwater streams or rivers merge with the ocean.
• In this extent, these areas are unique in terms of their salt concentration due to the mixing of the two waters. Microflora, such as algae, and macroflora, such as seaweeds, marsh grasses, and mangrove trees (only in the tropics), can be found here. In terms of fauna, there are a variety of worms, oyster, crabs, waterfowls in and around estuaries.