Figure 367. — Oyster reef in Altamaha Sound, Ga., at low tide, March 1925. The highest point was about 6 feet above 

 the bottom; water at the foot of the reef was 8 inches deep. The reef consists of live oysters growing on the side 

 and upper surfaces and attached to empty shells. 



oyster larvae will be retained in the estuary by 

 the end of the larval period. It is obvious that 

 the requirements of water movements for the 

 growing of oysters are different from those nec- 

 essary for the settlement of larvae. 



SALINITY 



The general rule that the composition of sea 

 water is constant and varies only in the degree 

 of dilution by fresh water is applicable to the 

 estuaries and other basins which have direct 

 communication with the sea. Only in exceptional 

 cases is the circulation in an estuary so impeded 

 that stagnation and oxygen deficiency develop 

 and render the area unsuitable for oyster growth 

 and reproduction. 



Oysters like many other euryhaline organisms 

 are able to live in sea water of very wide range 

 of salinity. According to the so-called Venice 

 system of classification of saline waters adopted 

 at the symposium organized by the International 



Association of Limnology and the International 

 Union of Biological Sciences at Venice, Italy, in 

 April 1958, the range of salinity favorable for 

 C. virginica falls within two zones, the polyhaline, 

 from 307oo to lS7oo, and the mesohahne, from 

 l<S%oto 57oo (Symposium for the Classification of 

 Brackish Waters, 1958). Populations of oysters 

 found beyond the upper or lower limits of the 

 range exist under marginal conditions. Their 

 growth and gonad formation are inhibited, and 

 they are often decmiated either by floods, in the 

 lower zone of the range, or by predators which 

 usually remain in more saline waters. The non- 

 commercial oyster of the Atlantic and Gulf 

 coasts, 0. equestris, prefers more saline waters 

 and has been found on buoys as far as 20 miles 

 offshore where surface salmities ranged from 33%o 

 to 36 7oo (Galtsoff and Merrill, 1962). In the 

 subtidal regions of the coastal waters this species 

 is fomid in salinities of 207oo to 257oo- 



404 



FISH AND WILDLIFE SERVICE 



