An assessment of the effects of some aspects of water quality on amphibian reproduction

Abstract

As a result of their quasi-terrestrial lifestyle, adult amphibians are generally believed to be less-affected by water quality compared to completely aquatic organisms. This study investigated the effects of sewage pollution on the early developmental stages of anurans or tail-less amphibians (frogs and toads). The methodology involved a field survey of anurans in varied ranges of water quality, and monitoring of anuran eggs and tadpoles in controlled water media in the laboratory. The results indicated that turbidity and dissolved oxygen content of water severely affected the survival of tadpoles (anuran larvae) and the ability of anuran eggs to hatch. LD50 values indicated that the eggs failed to hatch when dissolved oxygen and turbidity levels were below 2.9 mgl-1 and above 22 NTU respectively. At dissolved oxygen and turbidity values of 2.3 mgl-1 and 35 NTU respectively, 50% of tadpoles survived. The level of pollution in the urban stream used in the experiment required 87% dilution to support the hatching of anuran eggs and 82% dilution to support survival of the tadpoles. These required dilution levels could only be obtained after heavy rains, suggesting that in addition to preventing dessication of eggs and tadpoles, the anuran strategy of breeding after rains has an added advantage of minimizing the effects of pollutants on their early developmental stages.