THE EFFECT OF SALINITY ON CADMIUM TOXICITY IN THE ESTUARINE MYSID MYSIDOPSIS-BAHIA - ROLES OF OSMOREGULATION AND CALCIUM

Calcium exerted a sparing effect on Cd2+ toxicity in the bay mysid, My sidopsis bahia, although the effect was not as pronounced as effects t hat were due to Cd2+-salinity interactions. Molt rate, expressed as nu mber of exuviae recovered per mysid day, was significantly increased b y Cd2+-salinity interaction. Partial correlations of the number of dea d mysids with the number of molt casts recovered, when adjusted for th e independent effect of salinity on molt rate, were significant for mo st periods, suggesting that the observed increase in apparent molt rat e may actually reflect enhanced sensitivity of post-molt animals to Cd 2+. A slight, but statistically insignificant change in serum osmolali ty was observed after 24 h exposure to 3-62 mug/liter Cd2+ at the low test salinity of 12 parts per thousand in the first osmoregulation exp eriment. No effects on hemolymph osmoregulation were observed in the s econd experiment following exposure up to 48 h to similar Cd2+ levels at 12-30 parts per thousand salinity.