Title

Physiological, exfoliative cytological, histological, and biochemical responses of {\it Geukensia demissa\/} (Mollusca) exposed to dissolved copper at various salinities

Date of Completion

January 1988

Keywords

Biology, General|Environmental Sciences

Degree

Ph.D.

Abstract

This investigation assessed the interactive effects of copper exposure at various salinities on the ribbed mussels' Geukensia demissa using multiple criteria. It was hypothesized that the efficiency of the ribbed mussels' detoxification mechanism(s) largely dictated the degree of impairment and recovery of physiological, cellular and biochemical functions, as well as the extent of histopathological manifestations. In order to address this hypothesis, the physiological response (byssal thread attachment) and histopathological changes of copper exposed mussels at high (30 ppt) and low (10 ppt) salinities were determined, and the attendant cellular- hemocyte diapedesis and copper accumulation and molecular-copper binding to metallothionein-like protein (MTLP) parameters were obtained.^ Results of laboratory studies determined that copper effects on byssal thread attachment were enhanced by high salinity. Attachment of copper exposed mussels was reduced at all salinities; however, recovery of attachment varied inversely with salinity.^ Similar salinity mediated responses were encountered by examining exfoliated cellular elements. Hemocyte exudation by mussels occurred following copper exposure; low salinity further enhanced this response. Sloughing of ciliated gill epithelial cells occurred following copper exposure, and was greatest in mussels at the high salinity. These results indicate that the enhanced hemocyte exudation at low salinity may be a cellular mechanism by which excessive copper is eliminated, while sloughing of ciliated epithelial cells reflects damaged gill tissue.^ Corroborative histological examination of mussels revealed that intestinal epithelia and gill tissues were sites of hemocyte diapedesis. Copper exposed mussels had more hemocytes in intestinal and rectal lumina than the controls. Gill filaments of copper exposed mussels exhibited a high degree of tissue derangement, and is probably the source of sloughed ciliated epithelial cells. Histopathological alterations were also noted in the digestive and excretory tissues.^ Copper exposure quickly induced the synthesis of MTLP in mussels. Following copper exposure, mussels at high salinity had more copper associated with MTLP than mussels at low salinity, reflecting a greater excess of intracellular copper. Recovery of byssal attachment was correlated with a rapid disappearance of copper associated with MTLP. ^