What defines a keystone species in an aquatic environment?

A keystone species is defined as a species that has a disproportionately large impact on its ecosystem relative to its abundance. This means that the presence or absence of a keystone species can significantly influence the structure and dynamics of its environment. In aquatic ecosystems, keystone species can affect species diversity, the population sizes of other organisms, and overall ecosystem health.

Such species often play crucial roles in maintaining the balance of the ecosystem. For example, they might be top predators that control the populations of prey species, thus preventing overgrazing or overpopulation that could lead to habitat degradation. Other keystone species may provide critical resources or create habitats that support a wide variety of other organisms.

In contrast, a species with minimal ecological impact would not be considered a keystone species, as it does not contribute significantly to the structure or function of its ecosystem. Additionally, the specificity of habitats (freshwater or otherwise) does not determine a keystone species, as they can be found in various environments, including marine and freshwater. Competition with every organism is also not a defining characteristic of a keystone species since it is about ecological impact rather than sheer competitive ability.