Final answer:
Important variables affecting aquatic ecosystems include dissolved oxygen levels, light penetration, temperature, salinity, currents, and flow regime. These factors influence the living conditions within the ecosystem and the types of species that can survive there.
Step-by-step explanation:
Some important variables affecting aquatic ecosystems include the concentration of dissolved oxygen, light penetration, temperature fluctuations, salinity levels, water movements such as currents and tides, and the flow regime. Dissolved oxygen is crucial for aquatic life and is affected by water temperature and flow; colder water can hold more oxygen than warmer water, and faster-moving water is generally better oxygenated. Light penetration determines the depth at which photosynthesis can take place, influencing the distribution of producers and, consequently, the entire food web. Temperature influences metabolic rates of organisms and also affects the density and stratification of the water column, which can lead to different environmental conditions within an ecosystem.
Salinity - the salt content in water - can vary greatly between different aquatic ecosystems and is a critical determining factor for the types of species that can inhabit those waters. Water movement through currents and tides shapes nutrient distribution and availability, affecting everything from plankton migrations to the distribution of larger predatory species. Moreover, the flow regime of a river or stream can significantly impact the biological communities adapted to living in those conditions.