Final answer:
Estuaries are biomes where fresh water meets the ocean, resulting in a diluted saltwater mixture. They provide a protected habitat for young crustaceans, mollusks, and fish, and the salinity of estuaries can vary based on freshwater flow. High and low tides affect the movement of salt water in the estuary.
Step-by-step explanation:
Estuaries are biomes that occur where a source of fresh water, such as a river, meets the ocean. Therefore, both fresh water and salt water are found in the same vicinity; mixing results in a diluted (brackish) saltwater. Estuaries form protected areas where many of the young offspring of crustaceans, mollusks, and fish begin their lives. Salinity is a very important factor that influences the organisms and the adaptations of the organisms found in estuaries. The salinity of estuaries varies considerably and is based on the rate of flow of its freshwater sources, which may depend on the seasonal rainfall. Once or twice a day, high tides bring salt water into the estuary. Low tides occurring at the same frequency reverse the current of salt water.