Comparison of growth and mortality in juvenile sand dollars (Dendraster excentricus) as indicators of contaminated marine sediments

Abstract

A bioassay system involving exposure of juvenile sand dollars (Dendraster excentricus) to contaminated sediments from Puget Sound, Washington, was evaluated. In these bioassays, juvenile sand dollars were exposed to serially diluted sediments from three urban areas with different types and levels of contamination. Physical and biochemical measures of growth (i.e., length or diameter, DNA content, and protein content) were then evaluated for sensitivity and concentration responsiveness to a chemical gradient and compared with mortality as biological indicators of toxicant effects in sediments. Growth measurements appeared to be more sensitive indicators of contaminant exposure than mortality. Sediment mixtures with the highest proportions of contaminants were generally lethal to these organisms, but at lower sediment concentrations, where significant mortality did not occur, significant reductions in growth were observed. The results suggest that measurement of growth, either morphometrically or biochemically, in conjunction with mortality can provide better discrimination for assessing toxicity in sediment bioassay systems. Also, because impaired growth is a sublethal effect of contaminant exposure, it may be a useful indicator for assessing the long-term (chronic) effects of exposure to contaminants on marine organisms.