Figure 9. — Biologists conducting experiments with oyster larvae to determine their food requirements and the optimal 

 ranges of temperature, salinity, and other factors of the environment for larval development and growth. 



reached this stage. At 12.0 p.p.t. practically 

 no eggs of Long IslandSound oysters developed 

 into normal shelled larvae. 



The optimum salinity for shelled larvae 

 developed from eggs of oysters grown in Long 

 Island Sound at a salinity of 27.0 p.p.t. was 

 about 17.5 p.p.t. Good larval growth was also 

 recorded at 15.0 p.p.t., while at 12.5 p.p.t. 

 growth was appreciably slower, although some 

 larvae grew to metamorphosis even at this 

 salinity. At 10.0 p.p.t. the growth practically 

 stopped. This was true, however, only in rela- 

 tion to straight-hinge larvae, because the 

 older the larvae became, the better they with- 

 stood such lov/ salinity, although growth m all 

 size groups was significantly reduced. 



Another experiment used Maryland oysters 

 that grew and developed gonads in the upper 

 part of Chesapeake Bay, where the salinity at 

 the time of collection was only 8.7 p.p.t. 

 Spawnings were induced in salinities of 7.5, 

 10.0, and 15.0 p.p.t. Some discharged eggs 

 developed into normal larvae at 10.0 and even 

 7.5 p.p.t. although, in the latter, abnormally 

 small individuals were quite common. In gen- 

 eral, the optimum salinity for development of 



eggs of this group of oysters was between 12.0 

 and 15.0 p.p.t., while a salinity of about 22.0 

 p.p.t. was the upper limit for normal develop- 

 ment. 



Effects of Turbidity on Eggs and Larvae 



Until recently virtually nothing was known 

 of the ability of oyster eggs to develop and 

 larvae to survive in turbid waters. Recent 

 experiments with oysters native to Long Island 

 Sound demonstrated that natural silt is harm- 

 ful to eggs and larvae. Thus, in a concentra- 

 tion of 0.25 gram of silt per liter of water 

 (g./l.), only 73 percent of the eggs survive. 

 In a concentration of 0.5 g./l., only about 31 

 percent of eggs survive and continue to de- 

 velop. In stronger concentrations of 1 or 2 

 g./l. practically no eggs develop to straight- 

 hinge larval stage. 



Larvae were also significantly affected when 

 the concentration of silt was 0.75 g./l. At 

 concentrations of 1.5 g./l., or higher, growth 

 was negligible and no oyster larvae survived 

 to metamorphosis in concentrations of 3 and 

 4 g./l. However, some larvae may survive. 



16 



