Date of Award

1995

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

First Advisor

William B. Stickle, Jr

Abstract

Effects of environmental factor gradients on growth, molting and physiology of crabs within the genus Callinectes were examined. Juvenile blue crabs, Callinectes sapidus, were exposed to a range of dissolved cadmium concentrations at two salinities (2.5 and 25$\perthous$). 21-day LC$\sb{50}$'s were lower at 2.5$\perthous$ (19 $\mu$g l$\sp{-1}$) than at 25$\perthous$ (186 $\mu$g l$\sp{-1}).$ Crabs were exposed to Cd levels of 0, 50 and 100 $\mu$g l$\sp{-1}$ for bioenergetic measurements. Energy expenditure did not vary with cadmium. Scope for growth, energy consumption and energy absorption were unaffected by Cd at 25$\perthous,$ but decreased with exposure to cadmium at 2.5$\perthous.$. Juvenile lesser blue crabs, Callinectes similis, were exposed to a range of salinities to determine the effects of salinity on tolerance and bioenergetics. C. similis exhibited 21d LC$\sb{50}$'s of 2.6 and 60.8$\perthous$ at low and high salinity. Crabs were exposed to 2.5, 10, 25, 35 and 50$\perthous$ for bioenergetic measurements. Energy expenditure was highest at low salinity (2.5$\perthous$), and decreased as salinity increased. Energy absorption and scope for growth were greatest at 35$\perthous$. Total lipids and RNA:DNA were positively correlated with feeding rates but unrelated to salinity. Juvenile Callinectes sapidus and C. similis were exposed to three salinities over 67 days for measurement of growth and molting. C. sapidus growth was unaffected by salinity. C. similis exhibited decreased growth at 5 and 30$\perthous$ relative to 10$\perthous$, the effect being most pronounced when measured as dry weight increase. Growth per molt (wet weight) of C. similis increased with salinity, whereas that C. sapidus was unaffected. C. sapidus at low salinity (2.5$\perthous$) exhibited increased feeding rates by the end of the exposure period, whereas those of C. similis (at 5$\perthous$) decreased. Adult C. sapidus demonstrated superior osmoregulatory ability to juveniles. Adult C. similis from 30$\perthous$ osmoregulated at similar levels as juveniles, while adults from 22$\perthous$ exhibited osmoregulatory ability greater than that of juveniles, and insignificantly different from that of adult C. sapidus. Based on electrophoretic analysis of juveniles of the two species, Nei's genetic distance (D$\rm\sb N)$ between C. similis and C. sapidus was calculated as 0.41092.

Pages

137

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