Which factor most directly influences the distribution of aquatic species?

The distribution of aquatic species is significantly influenced by water temperature and quality because these factors directly affect the physiology and biology of aquatic organisms. Temperature plays a crucial role in determining metabolic rates, reproduction cycles, and overall species survival. Different species have specific thermal tolerances, and deviations from their optimal temperature ranges can lead to stress or death.

Water quality encompasses various elements such as pH, dissolved oxygen, nutrient levels, and the presence of pollutants, all of which are vital for maintaining healthy aquatic ecosystems. For instance, high levels of pollutants or low dissolved oxygen can create inhospitable environments for many species, thus shaping their distribution.

In contrast, while human activities and urbanization, seasonal changes in precipitation, and geographical barriers do have impacts on aquatic populations, they are often secondary to the immediate physiological needs that water temperature and quality fulfill. For instance, urbanization can alter water quality through runoff pollution, but the fundamental survival of aquatic species hinges more critically on the conditions of temperature and quality in their habitat at any given moment.