Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


The effects of salinity on cadmium toxicity to the bay mysid, Mysidopsis bahia Molenock were studied in a series of experiments examining salinity tolerance, effect of salinity on intermolt period, osmoregulatory capacity, interaction of salinity with acute cadmium toxicity, role of changes in cadmium speciation, modification due to calcium antagonism and effects of cadmium on osmoregulatory ability. Upper and lower tolerance limits increased with increasing acclimation salinity. Intermolt duration decreased slightly with increasing salinity. Mysidopsis bahia osmoregulates at salinities from 5 to 37&\perthous& and exhibits an isosmotic point of 24&\perthous&. Hemolymph osmolality attained steady-state condition by 95 min post-transfer to high and low salinity water. The 96-h LC&\sb{lcub}50{rcub}& (as total cadmium, Cd&\sb{lcub}\rm T{rcub}&) increased in a general linear fashion with salinity. When toxicity was expressed in terms of free cadmium ion (Cd&\sp{lcub}2+{rcub}&) rather than Cd&\sb{lcub}\rm T{rcub}&, CdCl&\sp+& or CdCl&\sb2& only a slight salinity effect was apparent, suggesting that Cd&\sp{lcub}2+{rcub}& is the primary toxic species. Mysids were more tolerant of Cd&\sp{lcub}2+{rcub}& at an intermediate salinity of 22&\perthous&. Toxicity of Cd&\sp{lcub}2+{rcub}&, when varied by use of the artificial ligand nitrilotriacetic acid (NTA), was independent of Cd&\sb{lcub}\rm T{rcub}& concentration at a given salinity but increased with increasing salinity and/or NTA concentration. Calcium exerted a sparing effect on Cd&\sp{lcub}2+{rcub}& toxicity although the effect was not as pronounced as were effects due to Cd&\sp{lcub}2+{rcub}&-salinity interactions. Molt rate was significantly increased by Cd&\sp{lcub}2+{rcub}&-salinity interaction. It is postulated that the increase in apparent molt rate may at least partially explain the residual salinity effect that is observed even when speciation and calcium effects are considered. No significant effects on hemolymph osmoregulation were observed following exposure for up the 48 h to Cd&\sp{lcub}2+{rcub}& levels approximating the 96-h LC&\sb{lcub}50{rcub}& at 12 to 30&\perthous& salinity.



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