Toxic effects of cadmium on fertilizing capability of spermatozoa, dynamics of the first cleavage and pluteus formation in the sea urchin Anthocidaris crassispina (Agassiz)

Abstract

Effects of cadmium on the fertilizing capability of spermatozoa, dynamics of the first cleavage and pluteus formation in the sea urchin, Anthocidaris crassispina, were investigated. Exposure to cadmium concentrations of 0.32, 0.56, 1.0, 1.8, 3.2, 5.6 and 10.0 mg l-1 for 30 min caused a significant adverse effect on the fertilizing capability of spermatozoa (EC50=1.7 mg l-1). For the first cleavage kinetics assay, eggs were pre-exposed to 0, 0.18, 0.32, 0.56, 1.0, 1.8, 3.2 and 5.6 mg l-1 of cadmium for 30 min. Fresh sperms of fixed concentrations were then added to the eggs and the percentage of divided zygotes estimated. Concentration-dependent toxic effects on the dynamics of the first cleavage in A. crassispina were observed between 0.18 and 5.6 mg l-1 cadmium. Calculation of EC50 values by probit analysis at different stages of the first cleavage revealed that EC50 values increased gradually from 0.37 mg l-1 at the beginning to 2.24 mg l-1 at the end of the cleavage process. Different larval classes (normal, abnormal and retarded plutei, preplutei, dead embryos/larvae) of A. crassispina obtained from eggs pre-treated with cadmium for 30 min and then exposed to cadmium throughout embryogenesis were also examined. The percentage of abnormal plutei was significantly higher than that of the control at 0.56 mg l-1 cadmium and higher. The 48 h EC50 calculated for the number of normal plutei was 1.5 mg l-1. A χ2-test revealed significant changes in the distribution of proportions of different larval classes only at cadmium concentrations ≥1.8 mg l-1. At 5.6 mg l-1 of cadmium, small malformed plutei, and oval embryos with rudimentary skeleton, poorly differentiated intestines and no mouth (pre-pluteus stage) were observed. The relative sensitivity of various end points to cadmium is also compared and discussed. Copyright (C) 1999 Elsevier Science Ltd.