Final answer:
Aquatic organisms depend on the availability of sunlight and the concentration of dissolved oxygen and nutrients in the water.
Step-by-step explanation:
One thing that aquatic organisms depend on that terrestrial organisms don't usually have to worry about is the availability of sunlight and the concentration of dissolved oxygen and nutrients in the water. Aquatic organisms rely on sunlight for photosynthesis and obtaining energy, and they require dissolved oxygen and nutrients for survival. These factors vary from place to place in a body of water and are used to define aquatic biomes.