LIFE SCIENCE

Detailed explanation-1: -In almost all estuaries the salinity of the water changes constantly over the tidal cycle. To survive in these conditions, plants and animals living in estuaries must be able to respond quickly to drastic changes in salinity. Plants and animals that can tolerate only slight changes in salinity are called stenohaline.

Detailed explanation-2: -Salinity in an estuary varies according to one’s location in the estuary, the daily tides, and the volume of fresh water flowing into the estuary. In estuaries, salinity levels are generally highest near the mouth of a river where the ocean water enters, and lowest upstream where freshwater flows in.

Detailed explanation-3: -Specially developed kidneys, gills, and body functions help prevent the water from equalizing salt concentrations across membranes through osmosis. Marine animals must also be able to absorb dissolved gases like oxygen from the water needed to release the energy from food.

Detailed explanation-4: -Many estuarine plant species are halophytes: plants that can tolerate salty conditions. Halophytic plants are adapted to deal with the salinity resulting from saltwater on their roots or from sea spray. In some halophytes, filters in the roots remove the salt from the water that the plant absorbs.