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

¹ Department of Biology, Box 19498, The University of Texas at Arlington, Arlington, Texas 76019
² Department of Biology, Syracuse University, Syracuse, New York 13210; and The Marine Biological Laboratory, Woods Hole, Massachusetts 02543.

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.