Table of Contents
What is the Aquatic Ecosystem?
- In contrast to terrestrial ecosystems, which are established on land, an aquatic environment is one that forms around a body of water.
- Aquatic ecosystems feature populations of creatures that are mutually and environmentally reliant.
- Marine and freshwater ecosystems are the two primary types of aquatic ecosystems.
- Freshwater environments can be lentic (including pools, ponds, and lakes), lotic (including streams and rivers), or wetland (areas where the soil is saturated or inundated for at least part of the time).
Features of Aquatic Ecosystem
Detailed characteristics of the aquatic ecosystem are depicted in the graphic below —
- Water Diversity – They may be composed of either freshwater or saltwater.
- Varied Habitat Population – They provide home for a wide range of vegetation and fauna, from shallow water to the deepest oceans.
- Exclusive Biodiversity – The majority of aquatic habitats’ flora consists of algae and corals.
- Rich Sustainment Network – They ensure the smooth continuity of the entire complex food chain, regulate the hydrological cycle, and function as a pollution filter.
Types of Aquatic Ecosystem
There are two types of Aquatic Ecosystems, including;
1. Freshwater Aquatic Ecosystem
- They comprise less than 0.8% of the earth’s surface.
- Freshwater consists of lakes, ponds, rivers and streams, as well as wetlands, swamps, bogs, and temporary pools.
- Freshwater ecosystems are classed as either lotic or lentic.
- As lentic environments, bodies of water such as lakes, ponds, pools, bogs, and other reservoirs are known.
- Whereas lotic habitats consist of moving water bodies such as rivers and streams, riparian habitats are characterised by still bodies of water.
a. Lotic Ecosystems
- They refer mostly to swiftly flowing, unidirectional waters, such as rivers and streams.
- These settings are home to numerous insect species, including as beetles, mayflies, and stoneflies, as well as several fish species, such as trout, eel, minnow, etc.
- In addition to these aquatic species, these ecosystems are home to a number of animals, including beavers, river dolphins, and otters.
b. Lentic Ecosystems
- They encompass all ecosystems with standing water.
- The most prevalent examples of Lentic Ecosystem are lakes and ponds.
- The term lentic primarily refers to water that is stationary or relatively still.
- Algae, crabs, shrimps, amphibians including frogs and salamanders, rooted and floating-leaved plants, and reptiles including alligators and other water snakes inhabit these environments.
- Wetlands are marshy environments that are occasionally covered in water and are home to an abundance of plant and animal species.
- Swamps, marshes, bogs, black spruce, and water lilies are some examples of wetland plant species.
- This habitat is home to dragonflies and damselflies, birds like the Green Heron, and fish like the Northern Pike.
2. Marine Aquatic Ecosystem
- The marine ecosystem covers the majority of the planet’s surface.
- Two-thirds of the planet is covered by water, which includes oceans, seas, the intertidal zone, reefs, the seafloor, estuaries, hydrothermal vents, and rock pools.
- Each species is unique and native to its environment.
- This is due to the fact that they have adapted to their ecosystem. Aquatic animals are incapable of surviving outside of water.
- Existence of exceptional cases demonstrates yet another instance of adaptations (e.g. mudskippers).
- The higher concentration of salts in the marine ecosystem makes it difficult for freshwater creatures to survive.
- Additionally, aquatic organisms cannot thrive in freshwater.
- Their bodies will enlarge if placed in less salty water since they are acclimated to saltwater (osmosis).
a. Ocean Ecosystems
- The Pacific, Indian, Arctic, and Atlantic Oceans are the five major oceans of our globe.
- The Pacific and Atlantic Oceans are the largest and deepest of these five oceans.
- These waters are home to around five million aquatic species.
- Shellfish, shark, tube worms, crab, small and large ocean fishes, turtles, crustaceans, blue whale, reptiles, marine mammals, seagulls, plankton, corals, and other ocean plants are a few of the animals that inhabit these environments.
b. Coastal Systems
- Coastal ecosystems are the open systems of land and water that are connected to form the coast.
- Coastal habitats differ in their structure and richness.
- At the bottom of the coastal ecosystem, a large range of aquatic plant and algal species can be found.
- The flora is diversified and includes primarily of crabs, fish, insects, lobsters, snails, and shrimp, among others.
c. Ocean Ecosystem
- There are five primary oceans on Earth: the Pacific Ocean, Atlantic Ocean, Indian Ocean, Arctic Ocean, and Southern Ocean.
- The Pacific Ocean is the biggest and deepest of these five, and the Atlantic is the second biggest.
- In addition, the Southern Ocean is home to the greatest Krill population.
- The oceans are home to numerous aquatic animals, including turtles, crabs, plankton, corals, shellfish, blue whales, sharks, tube worms, etc.
- Typically, it is the spot where a sea and a river meet, which makes the water somewhat saltier than freshwater and more diluted than the marine habitat.
- Estuaries are regarded as biologically productive because they boost primary production and trap plant nutrients.
- Examples of estuaries include tidal marshes, river mouths, and bays along the coast.
e. Coral Reefs
- They are affectionately known as the Rain Forest of the Oceans because they are home to a vast array of aquatic plants and fauna.
- A coral reef is an aquatic environment composed of reef-forming corals. In reef formation, coral polyps are bound together by calcium carbonate.
- The majority of coral reefs are composed of stony corals with grouping polyps.
- The animal phylum Cnidaria contains sea anemones and jellyfish, whereas coral belongs to the animal class Anthozoa.
- In contrast to sea anemones, corals generate hard carbonate exoskeletons that support and protect them.
- Most reefs want warm, shallow, clear, bright, turbulent water. At the start of the Early Ordovician, 485 million years ago, coral reefs replaced the microbial and sponge reefs of the Cambrian.
Plants and animals in aquatic ecosystems exhibit a vast array of adaptations, including life cycle, physiological, structural, and behavioural adaptations. The majority of aquatic organisms are streamlined, allowing them to reduce friction and conserve energy. Fins and gills are the respective locomotory and breathing organs. Unique characteristics of freshwater species allow them to remove surplus water. Aquatic plants have unique root structures that allow them to live in water. Some may have submerged roots, while others may have emergent roots or floaters such as water hyacinths.
Components of Aquatic Ecosystems
- Light: Solar radiation is the source of energy that keeps the system operational. Light penetration is affected by the amount of dissolved or suspended particles in water, as well as the number of plankton. Based on the amount of light penetration, an aquatic habitat can be divided into euphotic (eu=true, photic=light), mesophotic, and aphotic zones. In the euphotic zone, there is an abundance of light for plants and animals. In the aphotic area, no light exists.
- Inorganic substances: These include carbon, water, phosphorus, nitrogen, calcium, and other elements such as sulphur, depending on the ecosystem’s location. Carbon dioxide and oxygen, among other inorganic elements, are dissolved in water. Plants and animals both require water for nutrition and gas exchange. Reserves of phosphorus, nitrogen, sulphur, and other inorganic salts are found in the sediment and within living organisms. A little fraction of these salts can be dissolved.
- Organic compounds: Some of the natural organic substances found in the aquatic environment are amino acids, humic acids, and the decomposed remains of animals and plants. These particles are partially dissolved and suspended in water.
a. Producers or autotrophs
- Floating microorganisms and plants: These organisms are known as phytoplankton (“phyto”- plants, “plankton”- floating). It consists of microscopic organisms. Occasionally, they are so prevalent in a body of water that they cause it to seem green; for example, Spirogyra, Ultrix, Cladophora, Diatoms, and Volvox.
Rooted plants: These are structured in concentric zones from the perimeter to the deeper layers. With increasing water depths, the following three distinct zones of aquatic plants are observed:
- Emergent vegetation zone, including Typha, Bulrushes, and Sagittaria
- Rooted vegetation zone with leaves that float. e.g., Nymphaea
- Examples of submergent vegetation include pond weeds such as Hydrilla, Rupia, and musk grass.
Consumers are organisms that obtain their nutrients directly or indirectly from autotrophs, or producers, such as tadpoles, snails, sunfish, and bass. These creatures can be divided into the following categories:
- Neuston are unattached organisms that inhabit the air-water interface, such as floating plants. For instance, Cockroaches and backswimmers
- Periphyton are organisms that adhere to the stems and leaves of rooted plants or things that protrude above the surface of the mud, such as sessile algae and the group of animals connected with them.
- Zooplanktons are animals that float. For instance, Cyclops and Cypris.
- Nektons are organisms with the ability to freely float and navigate. Benthic species are those that inhabit the ocean floor, such as mollusks, mites, beetles, and certain crustaceans.
- They are dispersed throughout the entire aquatic ecosystem, but they inhabit the bottom of the body of water.
- These bacteria and fungus, such as Rhizopus, Penicillium, and Curvularia, feed on dead and decaying organisms.
Factors Affecting Aquatic Ecosystems
A. Natural Factors
By constructing and consuming dams, beavers can affect the structure and dynamics of aquatic ecosystems. The following adjustments are possible (Naiman et al., 1986):
- The creation of wetlands through flooding of the riparian zone; Alteration of channel hydrology and geomorphology; Changes in nutrient cycling and decomposition; Increased holding time of sediment and organic matter due to reduced velocities; Alteration of the riparian zone, including species composition and dynamics; Influence of habitat and, consequently, the overall species found in the altered habitat; and
- Effects on the materials moved downstream of the modified area.
The beaver’s ability to alter its environment and establish new habitats makes it a keystone species, as its extinction would have a negative impact on all species that depend on these habitats.
- Inundation is a crucial component of the natural hydrological cycle and the ecosystems it affects.
- Through floods, hydrological connectivity between floodplains and rivers is preserved.
- When a river floods, it deposits nutrient-rich sediment on the banks and washes into the river bits of plant that serve as food for aquatic life.
- In addition to replenishing floodplain lakes and ponds, flooding can also raise the water table.
- The perched basins in the Peace-Athabasca Delta, for example, are replenished by seasonal flooding.
- The introduction of flooding through damming or catastrophic events can be damaging to an aquatic ecosystem until equilibrium is restored.
- In the case of dams, achieving this equilibrium is merely a matter of time; as one habitat is destroyed, another is established.
- In the case of catastrophic flood events, equilibrium typically returns once the water has gone and aquatic organisms are able to rebuild their habitat in a nutrient-richer environment.
B. Human Influences on Aquatic Ecosystems
When people do things that affect aquatic ecosystems, they are more likely to mess up natural patterns and processes because species can’t adapt quickly enough to changes in their environment. The oil sands, pulp and paper mills, municipal waste, and, to a lesser extent, forestry and agriculture all have an effect on the lower Athabasca basin. Below, we talk about more general issues that come up when humans change aquatic ecosystems.
1. Bioaccumulation and Biomagnification
- Some pollutants that get into aquatic systems are stored in organisms, usually in fat tissue, instead of being released or passed out of the body. This is called bioaccumulation, and it means that the contaminant builds up over time.
- Biomagnification is the process by which contaminants become more concentrated in organisms higher up on food webs.
- Even if an organism at a low trophic level in a food web has low levels of a contaminant, the contaminant will be more concentrated in the organism that eats it because it will eat many of these organisms over its lifetime.
- As you go up the food web, contaminants get more concentrated. When there are more steps to the top predator, more pollution builds up.
- So, if everything else is the same, the top predator in systems with longer food webs usually has a higher level of pollution than the top predator in systems with shorter food webs.
2. Endocrine Disrupting Substances
- Endocrine disrupting substances (EDS) are types of pollution that can change how an aquatic organism grows, reproduces, and develops in general.
- EDSs can be found in agricultural pesticides, alkylphenolics (oil-removing detergents) found in industrial and municipal effluents, and natural hormones and synthetic steroids (like those found in contraceptives) found in agricultural runoff and municipal effluents.
- EDSs can cause deformities in fish embryos, make it hard for fish to have babies, and turn male fish into female fish.
3. Climate Change
- The Northern Rivers Basin Study (NRBS) did modelling that showed how global warming could lead to an earlier spring melt, more rain and snow, and more evaporation (NREI 2002).
- All of these changes could cause the water level in the Athabasca River to go down. If warmer temperatures cause ice jams to melt faster, the water level in lakes and ponds could go down because they won’t be able to fill up as quickly.
- If the water temperature goes up, fish like trout and burbot might not be able to live or reproduce as well (Hynes 1970).
- Because of this, warmer temperatures and changes in the amount of water could change the kinds of species that live in the oil sands region and how long they live.
4. Atmospheric Deposition
- Gases and small particles (PM) are put into the air by oil sands operations and pulpmills. Then, these things can be put on land or water through dry or wet deposition (when rain or snow bind to the gases or particulates).
- There are contaminants in the air, like sulphur dioxide (SO2) and nitrogen dioxide (NO2). Acid rain and the acidification of lakes and soils in the oil sands area are both caused by these gases.
- Mercury is a big problem in the Alberta rivers in the north. At the regional level, the coal power plants near Edmonton and the oil sands operations are the main sources of mercury pollution (NREI 2002). Mercury can travel for long distances in the air and eventually ends up in water, where it can be harmful to aquatic life.
Significance of Aquatic Ecosystems
- The health of aquatic ecosystems is very important for the health of the planet as a whole.
- Our planet is called the “blue planet” for a reason. The fish, weeds, invertebrates, and mammals in the seas, as well as the fish, weeds, invertebrates, and mammals in rivers, lakes, streams, marshes, and ponds around the world, are all important sources of biodiversity.
- The seas also help keep the global temperature stable and keep carbon out of the air.
- Even though we should all try to eat less fish, we can’t deny that fish and other aquatic species are important food sources for many animals that live on land (i.e. animals that live on land).
- Aquatic ecosystems recycle nutrients, clean water, prevent flooding, increase and keep streamflow, refill groundwater, and give wildlife a place to live and people a place to play.
- They help people in many ways, like by providing water for drinking and farming, places to play, and homes for fish that are important to the economy. They also contribute to biodiversity and ecological production.
What is a Photic Zone?
- The photic (or “euphotic”) zone is the area between the surface of the lake and where the light level is only 1% of the surface level.
- The depth of this zone is based on how clear the water is.
- In the photic zone, the process of photosynthesis takes place.
- There is both photosynthesis and breathing.
What is an Aphotic Zone?
- The bottom layers of aquatic environments, where light can’t get in and plants can’t grow, make up the aphotic zone (profundal zone). This part of the body is only used for breathing.
- From the end of the photic zones to the bottom of the lake is the aphotic zone.
What is Dissolved Oxygen?
- Fresh water has 10 parts per million by weight of dissolved oxygen on average.
- This is 150 times less than how much oxygen is in the same volume of air.
- Oxygen gets into the aquatic ecosystem through the interaction of air and water and the photosynthesis of aquatic plants.
- Dissolved oxygen leaves a body of water through the air-water interface and the breathing of organisms (fish, decomposers, zooplankton, etc.).
- When there is less than 3–5 ppm of oxygen in the water, many aquatic animals die.
- Frederick Grassle, J. (2013). Marine Ecosystems. Encyclopedia of Biodiversity, 45–55. doi:10.1016/b978-0-12-384719-5.00290-2
- Grassle, J. F. (2001). Marine Ecosystems. Encyclopedia of Biodiversity, 13–25. doi:10.1016/b0-12-226865-2/00186-3