Occupying the higher levels in the estuarine food web, the fish community integrates the complex of ecological interactions occurring at lower levels, and indicates the status of the estuary as nursery ground and center of production for juvenile stages of important species. In southern New England healthy eelgrass beds comprise an essential fish and shellfish habitat, providing protection and abundant food for juveniles of several species, including tautog, sea bass, squeteague, cunner, tomcod, winter flounder, sticklebacks, and scallops. These species are not only important in their own right, but also are preyed upon by larger fish of commercial and recreational value, such as striped bass and bluefish. The carrying capacity of estuaries, that is, the amount of fish production they can support, as well as the diversity of fish species sustainable, depends on the availability of suitable habitat and the proper physico-chemical environment. These are compromised with the advent of eutrophic conditions resulting from excess nitrogen in coastal waters.