Problem:
Summarize: Coping with Salinity Fluctuations Maintaining the proper salt and water balance of cells and body fluids is one of the greatest challenges facing estuarine organisms. Most estuarine organisms are marine species that have developed the ability to tolerate low salinities as a consequence of fresh water from rivers or melting glaciers (L Fig. 14.5). How far they can move up the estuary depends on just how tolerant they are. Most estuarine organisms are euryhaline species, that is, they tolerate a wide range of salinities. The relatively few stenohaline species, those that tolerate only a narrow range of salinities, are limited to the upper or lower ends of the estuary and rarely penetrate into the estuary proper. Stenohaline species can be either marine or freshwater in origin. Some species are adapted to live in brackish water, or water of intermediate salinity. Some of these species are stenohaline; others are euryhaline. Salinity adaptations in animals Becaus their marine background, most estuarine organisms face the problem of the water in estuaries being diluted with fresh water. Those having an internal salt concentration higher than that of the surrounding water tend to take on water through osmosis. Some animals adapt by simple changes in behavior. They hide in their mud burrows, close their shells, or swim away if the salinity drops. These strategies are not widespread in estuaries, however, and most organisms rely on other mechanisms. Soft-bodied estuarine animals, like many molluscs and polychaete worms, often maintain osmotic balance. Need Assignment Help?