THE EFFECTS OF PHYSICAL VARIABLES AND ACCLIMATION ON SURVIVAL AND OXYGEN CONSUMPTION IN THE HIGH LITTORAL SALT-MARSH SNAIL,MELAMPUS BIDENTATUS SAY.

Abstract

The physiological ecology of the salt-marsh pulmonate gastropod, Melampus bidentatus Say, was investigated in specimens from the Little Sippewisset saltmarsh, Cape Cod, Massachusetts. M. bidentatus is tolerant of submergence, surviving 2-3 days at 20° C and 14 days at 10° C in 25%-l00% seawater (SW). Snails acclimated at 10°C tolerated temperatures of 32.2°C-37.4°C, and snails acclimated at 20°C tolerated 35.2°C-40.7°C, when submerged in 0%-l00% SW. LD (T)50 in air was 44.5°C (10°C acclimated) and 44.7°C (20°C acclimated). Aerial weight-specific O2 consumption (vO2) was 3-5 times higher than aquatic rates. Aerial and aquatic VO2 was regulated (Q10, < 1.5) over the ambient temperature range in both acclimation groups. The VO2 of 10°C acclimated individuals was lower than 20°C acclimated specimens, a pattern of "reverse" acclimation associated with energy stores conservation. O2 debt occurred after 5 h anoxia. In addition, M. bidentatus compensates VO2 for hypoxia by increasing both uptake rates and the degree of O2 regulation of VO2 during decreasing O2 concentrations. M. bidentatus displays a ciradian rhythm associated with desiccation pressures, and thus VO2 is maximal during evening and minimal during daylight hours. Under the selection pressures associated with longterm aerial exposure in the high littoral salt-marsh environment, M. bidentatus has evolved the vast majority of physiological adaptations required for terrestrial life, except for its aquatic egg-masses and planktonic development.