What type of ecosystem is defined as either freshwater or marine?

The correct response identifies the aquatic ecosystem, which encompasses both freshwater and marine environments. Aquatic ecosystems are characterized by their water-based habitats and can be subdivided into freshwater systems, such as rivers, lakes, and wetlands, and marine systems, which include oceans, coral reefs, and estuaries.

These ecosystems support diverse forms of life, each adapted to the conditions present in their respective environments. For example, freshwater ecosystems are typically less saline and often have distinct organisms that thrive in these settings, whereas marine ecosystems have higher salt concentrations and host different species.

In contrast, a terrestrial ecosystem refers to land-based environments, which are not classified as either freshwater or marine. Urban ecosystems focus on human-dominated areas, while desert ecosystems are characterized by extremely arid conditions. Thus, only the aquatic ecosystem correctly describes environments defined by the presence of water, making it the appropriate answer.