The diminution of light energy with depth by light scattering and absorption is called light attenuation. The light intensity or irradiance depends on the light intensity at the surface, light attenuation coefficient, and depth, with which it decreases exponentially. Light availability is a function of a complex interaction of factors which are directly or indirectly related to water quality such as total suspended solids, amount of phytoplankton, levels of nitrogen and phosphorus. In Chesapeake Bay a large scale decline of SAV occurred in the late 1960s and early 1970s. This decline was related to increasing amounts of nutrients and sediments resulting from development of the bay s shoreline and watershed.
Water quality is the key to restoring grasses to the bay.
The critical values that correspond to SAV survival have been determined for different salinity regimes. Some of the fish that use the bay as a nursery included striped bass, weakfish, shad, alewife, blue-back herring, croaker, and kingfish. Pollution, overharvesting, disease, and loss of habitat are blamed for continued decline in harvestable population of oysters and blue crabs. Diseases caused by the parasites MSX and Dermo are the major cause of recent decline in oysters population. Oysters and other filter feeders help maintain water quality by filtering suspended organic particles out of the water.