Cadmium effects on the carbon and energy balance of mudsnails

The present study examined the ability of shortterm physiological measurements to predict growth rates of a gastropod, Hydrobia ulvae, in response to pollutant exposure. Whereas growth rates of snails collected from Munkebo Harbor, Funen, Denmark in 1989 were substantially reduced by exposure to cadmium after ca. 3 wk, we could detect no change in total carbon balance measured in short-term radioisotope experiments. At 23‰ S, the reduction in percent growth after 3 wk was 186.4 for snails exposed to 100 μg Cdl^-1 and 225.7 for snails exposed to 200 μg Cdl^-1. At 13‰ S, the reduction in percent growth was 102.6 at 100 μg Cdl^-1 and 106.4 at 200 μg Cdl^-1. We found no effect of cadmium on sediment egestion rate over 18 d of exposure. Nor could we detect effects on carbon absorption efficiency or metabolic loss of absorbed carbon during the first 24 h following its ingestion. The fractional loss of ¹⁴C from uniformly-labeled snails showed a decrease in CO₂ and an increase in dissolved carbon in snails exposed to 200 μg Cdl^-1. Such changes in the partitioning of carbon loss from body stores suggest a partial shift from aerobic to anaerobic metabolic pathways which could reconcile the seeming disparity between growth and carbon balance in response to cadmium exposure.