What is a defining characteristic of aquatic biomes?

A defining characteristic of aquatic biomes is water salinity. Salinity, or the concentration of salts in water, is crucial because it influences the types of organisms that can survive in a given aquatic environment. For example, freshwater biomes, such as rivers and lakes, have low salinity, while marine biomes, such as oceans and seas, have high salinity. This difference dramatically affects the biodiversity and ecological dynamics of these environments, shaping the adaptations of organisms living there.

While temperature variations play a role in aquatic biomes, they are not as defining as salinity. Plant diversity is more of an outcome of the conditions in an ecosystem rather than a defining characteristic of the biome itself. Similarly, soil type is less relevant in aquatic environments where water, rather than soil, is the primary medium influencing the organisms present. Thus, salinity is the key defining feature that sets apart different aquatic biomes.