Journal of the Marine Biological Association of India

Volume 30 Issue 1&2

Toxicity of heavy metal cadmium on the ontogeny of the estuarine Hermit crab Clibanarius longitarsus (De Haan).

P. S. Lyla, S. Ajmal Khan and R. Natarajan

The 96 hr LC50 value for cadmium was found to be 270 ppb. Presently larval development was studied in 9 sublethal concentrations (10, 20, 30, 40, 50, 75, 100, 150 and 200 ppb). Two series of experiments were conducted. In the first series effect of cadmium on whole development was studied. In the second series effect of this metal on individual zoeal stages was studied. In both the series of experiments as the test concentration increased survival rate of larvae decreased. The survival rate was comparatively low in the second series. In the first series larval development was completed in all the test concentrations, but in the second series, development proceeded only upto 75 ppb concentration in II zoea, upto 100 ppb in III zoea and upto 40 ppb in IV zoea. Previous history of larvae was thus found to have a definite say on the survival rate. When the larvae were raised right through in test concentrations of pollutants, they develop a resisting capacity and fared comparatively better than the larvae introduced into the medium afresh. The overall time required for the completion of zoeal development increased with increase in test concentrations in the first series. In the second series, the intermoult duration in some lower test concentration was found to be shorter than that of control and higher concentrations. All the test concentrations of the first series fitted in with the definition of chronic concentration by Epifanio (1979). In the second series it was not so and it varied in different zoeal stages.

Date : 31-12-1988