Ecological implications of a freshwater impoundment in a low-salinity marsh

A three-year study of a low-salinity marsh area in the Galveston Bay System of Texas revealed that certain of the marsh waters were prime habitat for the postlarvae and/or juveniles of several marine crustaceans and fishes, including commercial shrimps, Gulf menhaden, Atlantic croakers, sand seatrout, and southern flounder. Results of this and other investigations indicated that shallow, turbid, soft-bottomed lakes and blind bayous in the interior of marsh areas are the 'target' habitats of many migrating young marine animals. Comparative catches per effort using the same gear in various portions of the Galveston estuary show, in general, that peripheral marsh waters can be much more productive per unit area than the more expansive open waters of the bays. There are further indications that brackish marshes associated with the upper estuary are more productive for some species than higher-salinity marshes of the lower bays. Therefore, a 7,200-acre section to be impounded in the Trinity River Delta, Chambers County, Texas, cannot be regarded as roughly equivalent in importance as 'nursery habitat' as any other 7,200-acre area in the Galveston Bay System. The inability to make reliable estimates of the absolute value of a given estuarine habitat has been invoked as ground for disregarding possible losses to the commercial fisheries. If special habitat types within an estuary are to be protected from destruction, biologists must devise methods for estimating the absolute values of such habitats in terms of their ultimate contribution to fisheries harvests