Aquatic ecosystems encompass a wide array of water ecosystems found on Earth, including both freshwater and marine environments.

On the surface, freshwater ecosystems consist of lakes, rivers, and freshwater wetlands, while marine ecosystems encompass coastal and bay ecosystems, coral reefs, coastal wetlands, offshore areas, and deep-sea habitats.

Each level of the water ecosystem occupies a distinct space and comprises interacting biotic and abiotic components, forming a cohesive entity with specific structures and functions through material cycles and the flow of energy and information.

Due to their extensive coverage, aquatic ecosystems play a vital ecological role, surpassing that of terrestrial ecosystems.

The abiotic components of water ecosystems include the medium in which organisms reside, such as the water body and its bottom. These components determine the water temperature, salinity, depth, current, and light levels in which organisms live.

Additionally, they encompass inorganic substances (such as carbon, nitrogen, and phosphorus) participating in material cycles, as well as organic compounds, such as proteins, carbohydrates, lipids, and humic substances, which connect the living and non-living organisms.

The biological components within aquatic ecosystems can be categorized into five major ecological groups based on their lifestyle: floating organisms, planktonic organisms, swimming organisms, benthic organisms, and periphytonic organisms.

Furthermore, based on their ecological function, these organisms can be classified into four categories: producers, consumers, decomposers, and organic debris.

One distinguishing feature of water ecosystems, setting them apart from other ecosystems, is the presence of water as a unique environmental factor. The characteristics of water significantly influence other factors within the ecosystem.

For instance, seawater can have a salinity level as high as 35‰, while freshwater typically ranges between 0.05‰ and 0.5‰, with estuarine waters experiencing variation due to tidal activity.

Apart from a few species capable of regulating the osmotic pressure and freely transitioning between freshwater and seawater, most aquatic organisms can only tolerate specific salinity ranges. Consequently, we observe the differentiation between freshwater and marine organisms.

Freshwater ecosystems are generally divided into two types: stagnant water and flowing water. The former includes freshwater lakes, marshes, ponds, and reservoirs, while the latter encompasses rivers, streams, and drains.

The structure of freshwater ecosystems not only varies between stagnant and flowing water types but also displays significant differences among different habitats of the same type.

Based on three habitat types within stagnant water ecosystems, hydrostatic communities can be classified into littoral zone communities, water zone communities, and deep-water zone communities.

The relative significance of these communities is primarily determined by the proportionate size of the three habitats within the water body. In general, the littoral zone serves as the primary production area in ponds, whereas lakes and reservoirs predominantly exhibit high productivity within the open water zone.

Aquatic ecosystems encompass a diverse range of water-based environments, including freshwater and marine ecosystems. These ecosystems consist of biotic and abiotic components, with water playing a crucial role.

The salinity of water varies between freshwater and marine environments, leading to the differentiation of organisms adapted to specific salinity ranges. Freshwater ecosystems are further divided into stagnant and flowing water types, each exhibiting unique structures and variations within different habitats.

Understanding the complexities and characteristics of aquatic ecosystems is vital for preserving and managing these essential components of our planet's biodiversity.