Aquatic Ecosystem (Meaning and Explanation)

We explain what aquatic ecosystems are, how they are classified and what their characteristics are. Also, examples of aquatic ecosystems.

What is an aquatic ecosystem?

An aquatic ecosystem is any ecosystem that It develops in a body of water of diverse size and nature which includes seas, lakes, rivers, swamps, streams, lagoons and coasts. The nature of water, its cycles, as well as the organic content present in it, both from natural and sedimentary sources (soils), play a vital role in them.

Organisms of aquatic ecosystems

Aquatic ecosystems contain three fundamental ecological categories of organisms: plankton, which float freely; the nekton, which swims with intensity; and the benthos, which moves at the bottom.

Plankton. It usually consists of small or microscopic organisms that are relatively weak swimmers. Most plankton is carried adrift by currents and waves. Plankton is usually divided into two main categories:
- Phytoplankton. They are photosynthetic bacteria and free-floating algae, that is, producers that form the basis of most aquatic food webs.
- Zooplankton. They are non-photosynthetic organisms that include protozoa, tiny crustaceans, and the larval stages of many animals.
Necton. They are larger organisms that swim actively, such as fish, turtles, and whales.
Benthos. They are organisms that live on the bottom of the sea that fixate on one point (sponges, oysters and crabs), take refuge in the sand (many worms and echinoderms), or walk or swim on the surface (lobsters, larvae of aquatic insects and starfish).

Types of aquatic ecosystems

Aquatic ecosystems are broadly divided into ecosystems maritime (those belonging to the ocean and its coasts) and ecosystems of fresh water (rivers, lakes, lagoons and streams), because according to the physical and chemical characteristics of each one, they will have a different fauna and flora, adapted as best as possible to the vital conditions.

Marine ecosystems

marine ecosystems are extremely varied and rich in fauna and flora in a wide range from microorganisms, marine mammals, fish, mollusks, to large predators and static and mobile plant forms. Let's remember that life on the planet comes from there. The immense and complex marine environment is subdivided into several zones:

Intertidal. It is the area in which the sea connects with the land, either on the surface or underground. It is an area of much change and great movement and erosion. The high levels of light and nutrients, along with the abundance of oxygen, make the intertidal zone a biologically productive environment. Seaweed and invertebrate animals predominate.
ocean floor. Also called the benthic environment, it is divided into zones according to their distance from land, light availability and depth. Characterized by low temperatures and lower incidence of light, it consists of sediments (mainly sand and mud) where many marine animals such as worms and clams are found. Benthic communities in shallow marine waters include seagrass beds, kelp forests (the largest known brown algae), and coral reefs. The abyssal zone is the part of the benthic environment that extends from a depth of 4000 to 6000 m. The hadal zone is the part of the benthic environment deeper than 6000 m.
Open sea. Also called the pelagic environment, it is the most densely populated region with the highest temperatures, which gradually decrease as the altitude decreases. It is divided into:
- The neritic province. It consists of shallow waters that cover the continental shelf, that is, the ocean floor from the coast to a depth of 200 m. Organisms that live in the neritic province are floaters or swimmers. There are plenty of phytoplankton, particularly diatoms in colder waters and dinoflagellates in warmer waters. Zooplankton includes tiny crustaceans, jellyfish, protists; such as foraminifera, and larvae of crabs, sea urchins, worms and crabs. Herring, sardines, squid, manta rays, whales, sharks, tuna, dolphins and toothed whales are also present.
- The oceanic province. It makes up most of the ocean and covers the deep sea basin, that is, the seabed at depths greater than 200 m. It is the largest marine environment and contains about 75% of sea water. It is characterized by having cold temperatures, no sunlight, a low presence of organic matter (although it has a constant rain of waste from the upper layers), gigantic aquatic pressures and a fauna adapted to these extreme conditions of darkness and lack of food, whose forms and survival mechanisms are often striking or surprising.

Characteristics of an aquatic ecosystem

Aquatic ecosystems are numerous and abundant in life, so usually have complex trophic chains of animals adapted to the specific conditions of the water: its salinity, its currents, etc. In the case of rivers, much will depend on the terrestrial elements carried or dissolved by the current, as well as the presence or absence of mineral or organic matter in the soils it runs through.

With the exception of aquatic amphibians and reptiles, many of which thrive in the water but return to land to lay eggs (or vice versa), most animals in these ecosystems are adapted to permanent immersion in water so they depend on their biotic balance.

The same goes for the flora, mostly composed of algae and other photosynthetic forms which are abundant in the most superficial regions, where there is more sunlight. In swamps, on the other hand, where the water is dark and full of organic remains, organisms adapt to the low concentration of oxygen.

Examples of aquatic ecosystem

Some examples of aquatic ecosystems are:

Mangroves. They are characterized by their dense and dark waters, with little movement. Their soils are usually clayey and covered with decomposing organic matter. Small fish and amphibious life forms predominate, as well as mangroves, trees whose characteristic roots protrude from the water.
Coastline. The coasts of warm seas are particularly abundant in animal and plant life, and that is why they are the most common fishing regions. Coral reefs, schools of fish and various food chains make up its blue waters.
Ponds. Characterized by waters with very little movement and a high presence of organic matter from neighboring trees, they usually host an enormous variety of microscopic life, as well as small fish and insects.
polar ocean. The icy waters of the poles, abundant in icebergs and frozen land, also host minimal flora (usually bacterial), and various animals adapted to the intense cold, such as aquatic mammals and cold-water fish.
coral reefs. They form as coral organisms (scleractinian cnidarians)) secrete calcium carbonate (CaCO₃). They are found in warm marine waters (whose temperature is usually greater than 21 °C), shallow and with low nutrient content. Coral reef ecosystems are the most diverse of all marine ecosystems, containing hundreds or even thousands of species of fish and invertebrates, such as giant clams, sea urchins, starfish, sponges, sea fans and shrimp.