explain how the salinity (salt concentration) of an estuary affect the kind of organism that live there?

Explanation: An estuary is an area where the river water meets the seawater to form mixed water known as brackish water. Salt concentrations reduce during the spring season as snowmelt and this increases freshwater flow in the seas and oceans. As a result, salinity decreases in the estuarine region. On the other hand.., during summer, the levels of salt rise as water evaporates leaving much salt in the estuarine. Therefore, salinity reduces during spring and increases during summer. 

The resulting higher salinity, or saltiness of the water, could harm plants and animals, alter fish and bird habitat, and reduce the capacity of estuaries to provide such important services as seafood production and the protection of shorelines from erosion. 

Salinity also affects chemical conditions within the estuary, particularly levels of dissolved oxygen in the water. The amount of oxygen that can dissolve in water, or solubility, decreases as salinity increases.