An aquatic ecosystem is a community of organisms and their interactions in a water environment. This type of ecosystem doesn't have to be large. A drop of water contains an entire aquatic ecosystem because the microorganisms in that drop of water are independent of outside organisms and completely supported by that small amount of water.
An aquatic ecosystem contains a large variety of life, from fish and reptiles to microscopic organisms such as bacteria and fungi. There are several types of aquatic ecosystems including marine ecosystems and freshwater ecosystems.
A marine ecosystem is a salt water ecosystem and the largest aquatic ecosystem in the world. A marine ecosystem, in turn, is divided into smaller ecosystems or zones. For instance, a coral reef is its own ecosystem as are lagoons and intertidal zones. These ecosystems contain algae, corals, fish and sharks.
Another major type of aquatic ecosystem is a freshwater ecosystem, which consists of lentic or slow-moving water ecosystems, lotic or fast-moving water ecosystems and wetland ecosystems. Lentic ecosystems include ponds and lakes, which break down into smaller zones or ecosystems including littoral zones, open-water zones and deep-water zones. Lotic ecosystems include rivers and streams. While lentic and lotic ecosystems are rich in fish, wetland ecosystems largely contain vascular plants and a variety of animal species.