What are examples of biological controls in aquatic systems?

Biological controls in aquatic systems refer to the use of living organisms to manage populations of harmful or unwanted species, thereby controlling issues such as weeds, algae, or pests without the use of chemical treatments. The correct choice highlights organisms that directly interact with one another in the ecosystem.

Parasites, predators, competitors, and herbivores are all integral parts of aquatic ecosystems that can help regulate populations. For instance, predators can reduce the numbers of prey species, herbivores can limit the growth of aquatic plants by consuming them, and competitors can inhibit the growth of certain species by competing for the same resources. By introducing or promoting these biological agents, one can maintain a balanced ecosystem and manage unwanted organisms in a more natural and sustainable way.

Other options present factors related to aquatic management but do not encompass biological control methods effectively. Herbivorous fishes and fertilizers involve a mix of biological and chemical techniques but do not specifically focus on biological control. Nutrients and chemical treatments emphasize a more synthetic approach, while aerobic bacteria and oxygen levels address aspects of ecosystem health rather than directly managing species populations. Thus, the focus on organisms actively involved in ecological relationships makes the correct choice the most relevant example of biological controls in aquatic systems.