What is the biggest difference between the aquatic biomes?

Water surrounds us everywhere. Being the largest part of the biosphere, it covers nearly 75% of the Earth's surface. Aquatic areas house numerous species of animals, large and small, and plants. This is also where life basically started billions of years ago when amino acids started to form together in the water. Today, without water, no life would be able to sustain itself and the earth would be a barren, desert-like place.

The aquatic biome can be broken down into two basic areas, (i.e, ponds and rivers) and (i.e, oceans and estuaries). The only thing that links all the areas together is that there is water. Obviously, aquatic areas tend to be a little humid and the air temperature slightly on the cool side, even though the temperature of the water can vary widely.

Freshwater Regions
As you might guess from the name, the water is fresh, meaning that there is a low salt concentration, usually less than 1%. Other characteristics of freshwater regions are that the plants and animals in the region 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 will talk about the different characteristics of each of these three freshwater zones.

Ponds and Lakes
These regions range in size of just a few square meters to thousands of square kilometers. Scattered throughout the earth, 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 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 (like diatoms), 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, which is basically the 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 4 C near the bottom to 22 C at the top. During the winter, the temperature at the bottom would be 4 C 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 4 C. 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.

Streams and Rivers
These regions are bodies of flowing water moving in one direction. They can be found everywhere, and their exact origin is not really known.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. 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. They include pond lillies, cattails, sedges, tamarack, and black spruce. The flora also includes such species as cypress and gum are found in the marshes. 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. By the way, wetlands are not 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.

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 is 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. Due to this, 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 causes 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 is all the water that is not near the shore or 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, 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.

Below the pelagic zone lies 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 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 is the area 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, and/or dead organisms. In this zone, the 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.

What is the major difference between the two aquatic biomes?

Aquatic biomes can be generally classified based on the amount of salt in the water. Freshwater biomes have less than 1% salt and are typical of ponds and lakes, streams and rivers, and wetlands. Marine biomes have more salt and are characteristic of the oceans, coral reefs, and estuaries.

What determines the different aquatic biomes?

Aquatic biomes are influenced by sunlight, availability of nutrients, salt level, and concentration of dissolved oxygen. Other abiotic factors that influence the biome are suspended particles and minerals because of runoff and water flow.

What is special about aquatic biomes?

Aquatic biomes are probably the most important of all the biomes. Their medium, water, is a major natural resource. Water is the basis of life, it supports life, and countless species live in it for all or part of their lives. Freshwater biomes supply us with our drinking water and water for crop irrigation.

What are the different types of aquatic biomes?

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