Organisms that live in coastal areas/estuarie s must adapt to changes in a water level and salinity b sunlight C oxygen d precipitation

The correct answer is a) water level and salinity.<br /><br />Organisms that live in coastal areas or estuaries must adapt to changes in water level and salinity. Estuaries are the areas where freshwater from rivers and streams mix with saltwater from the ocean, creating a unique environment with varying levels of salinity. The water level in estuaries can also fluctuate due to tides, storms, and other factors.<br /><br />Organisms in these areas have developed various adaptations to cope with the changing water levels and salinity. For example, some species can tolerate a wide range of salinity levels, while others have specialized mechanisms to regulate their internal salt concentrations. Additionally, many coastal organisms are adapted to the variable water levels, with some species able to burrow in the mud or attach to substrates during low tides.<br /><br />While sunlight, oxygen, and precipitation are also important factors for coastal organisms, the most significant challenge they face is the fluctuation in water level and salinity, which is the defining characteristic of estuarine environments.