This document is intended for educational purposes only and does not necessarily represent the viewpoint of agencies and commissions having regulatory authority over riparian lands. The most obvious function is that of habitat. For example, extensive beds of steamers and other clam species are found in mudflats along the sides and bottom of many tidal estuaries and creeks. Oysters tend to be even more directly connected to tidal rivers and other waterbodies where freshwater inputs result in reduced salinity levels. The reason for this habitat preference is that oysters can tolerate less salty water while one of their major predators, the whelks, cannot.
Shellfish are by no means confined to salty habitat, however.
As such, they depend on a healthy supply of microorganisms which in turn receive a significant proportion of their sustenance from nutrients contributed by rivers and streams. Organic detritus such as decaying leaves, twigs and other residue from streamside vegetation falling into the water fuels the base of the aquatic food chain. Filter feeders, such as shellfish, are located near the bottom of this chain and so are particularly influenced by the quantity and quality of the nutrients contributed to the ecosystem by riparian areas. In either case, naturally vegetated riparian areas along rivers and streams act as living filters to intercept and absorb excess nutrients, pathogens, and other pollutants carried along in runoff from adjacent development as well as by the river itself. This is accomplished by several biochemical processes, including the uptake of excess nutrients and heavy metals into living plant tissues and the breakdown of these and other pollutants into less harmful substances by beneficial soil bacteria.