Life in an estuary revolves largely aroundthe need to adapt to extremes in salinity,temperature, and other physical factors. Though other marine environments may be more extreme—they may be colder ormore saline, for instance—none changesso rapidly or in so many ways as an estu-ary. Living in an estuary is not easy, sorelatively few species have successfully adapted to estuarine conditions.
Coping with Salinity
Maintaining the proper salt and water bal-ance of cells and body fluids is one of thegreatest challenges facing estuarine organ-isms (see “Regulation of Salt and WaterBalance,” p.79). Most estuarine organismsare marine species that have developed theability to tolerate low salinities (Fig. 12.5).How far they can move up the estuary de-pends on just how tolerant they are. Most