Brackish Water

Brackish environments include estuaries, mangroves, coastal marshes, and some inland seas (the Baltic Sea averages 7–8 ppt; the Caspian Sea ~12 ppt). These highly productive habitats serve as nursery grounds for many commercially important marine species — juveniles of striped bass, flounder, and numerous reef fish use brackish estuaries for their first months of life. The abiotic stress of fluctuating salinity reduces species diversity but specialists like mudskippers, gobies, and glassfish reach high densities. Euryhalinity requires flexible osmoregulatory machinery and carries a significant energetic cost compared to stenohaline existence.