165 
salmon, oyster, crab, clam, menhaden, flatfish).? The recreational 
value resulting from estuarine dependent species is difficult to esti- 
mate; however, salt water fishermen spent $800 million in 1965, A 
user benefit scheme developed by the FWQA gives a crude estimate of 
the recreational value of estuaries as $300 million.® None of these 
estimates of estuarine value include multiplier effects. 
Species utilize and depend on the estuarine environment in dif- 
ferent ways. The variability of temperature and salinity, both sea- 
sonal and spatial, appears to be an important factor in the lives of 
estuarine species. The estuary is a fertile region, protected from out- 
side predators that cannot stand the fluctuations or absolute levels of 
temperature and salinity characteristic of an estuary. The marsh 
grass Spartina inhabits the muddy banks of the estuary and is a pri- 
mary source of food for many organisms. Oysters and clams use the 
estuarine bottom and depend on the tidal currents to circulate food 
to them and carry away their wastes. The menhaden requires the 
lowered salinity of estuarine water for proper metamorphosis and 
growth. The striped bass and the shrimp use the estuary as a nursery. 
The salmon uses the estuary as a passage zone to the fresh water in 
which they spawn. 
THE ESTUARINE ENVIRONMENT 
The estuarine environment can be characterized by three param- 
eters: the shape of the estuary, the water of the estuary, and the 
circulation in the estuary. The ecology of the estuary depends signif- 
icantly on each parameter. The parameters are listed below and their 
biologic importance is indicated. The parameters interact to some 
degree as a result of the variability and complexity of the estuarine 
environment. Although superficial, these parameters help to describe 
the important aspects of the estuary. . 
Estuarine flow 
Circulation pattern—direction and speed of currents. Tidal flow 
generally dominates. Circulation influences the sedimentation pattern. 
distribution of water properties, temperature, salinity, etc. 
Flushing time—how fast estuarine water is replenished and replaced 
een river water and seawater. Important for pollution and plankton 
growth. 
Variations in flow, seasonal and tidal—variations are characteristic 
of estuaries. 
Turbulence—degree and rate of vertical mixing. May affect plant 
growth, chemical distributions. 
Stream inflow—amount of fresh water entering the system, time 
distribution of flow. Strongly affects salinity distribution. 
Estuarine water properties 
Chemical content— 
Dissolved oxygen—may limit animal populations, strongly 
affected by sewage discharge. 
Toxic pollutants—may be lethal or harmful to populations. Oil, 
heavy metals, pesticides. 
5 FWQA, p. 151. 
6 FWQA, pp. 153-155. 
