Marine And Coastal Ecosystems Zones, Features, And Processes Practice Test

Freshwater inflows shape coastal salinity regimes by diluting seawater near shore, creating brackish zones with a gradient from salty to lower salinity water as rivers mix with ocean water. This change in salinity strongly influences which species can persist in the area. Organisms that require high salinity tend to decline where river input is strong, while species that tolerate or prefer lower salinity—brackish and euryhaline species—become established. Estuaries and other coastal zones often host communities that rely on this variability, including migratory and resident species that move with changing salinity, and those adapted to fluctuating conditions. The resulting assemblage can include habitats that serve as nurseries and feeding grounds due to the mix of waters and nutrients. In short, freshwater inflows lower nearshore salinity and drive shifts in species composition toward more tolerant or adaptable organisms.