EFFECTS OF TURBIDITY-PRODUCING MATERIALS IN SEA WATER ON EGGS AND LARVAE OF THE CLAM (VENUS (MERCENARIA) MERCENARIA)

¹ U. S. Fish and Wildlife Service, Milford, Connecticut

1. Some clam eggs developed normally in concentrations of 4.0 g./l. of clay, precipitated chalk or finely ground Fuller's earth, although the percentage developing normally decreased as the concentration of these suspended materials increased.

2. In silt concentrations below 0.75 g./l. the percentage of clam eggs developing normally was not significantly different from that in control cultures but decreased progressively in successively higher concentrations.

3. None of the clam eggs developed normally in silt concentrations of 3.0 or 4.0 g./l.

4. Larvae resulting from clam eggs developing in high concentrations of each of the suspended materials were reared to metamorphosis after being returned to normal sea water at 48 hours.

5. Clam larvae were unable to grow in concentrations of clay, chalk or Fuller's earth as high as those at which some eggs developed.

6. The highest concentration of chalk was 0.25 g./l. and 0.5 g./l. was the highest concentration of clay and Fuller's earth at which clam larvae showed any growth and mortality exceeded 90 per cent at all higher concentrations.

7. In a silt concentration of 0.75 g./l. growth of clam larvae was approximately normal and at lower concentrations was slightly faster than that of larvae in control cultures.

8. In silt concentrations of 1.0 to 2.0 g./l. growth of clam larvae was retarded and at 3.0 and 4.0 g./l. growth was negligible.

9. Even at a silt concentration of 4.0 g./l. there was no appreciable mortality of clam larvae within 12 days.