Reference: Biol. Bull. 161:246-269. (October, 1981) THE EFFECTS OF PHYSICAL VARIABLES AND ACCLIMATION ON SURVIVAL AND OXYGEN CONSUMPTION IN THE HIGH LITTORAL SALT-MARSH SNAIL, MELAMPUS BIDENTATUS SAY. 1 ROBERT F. MCMAHON 2 AND W. D. RUSSELL-HUNTER 3 2 Department of Biology, Box 19498, The University of Texas at Arlington, Arlington, Texas 76019; ^Department of Biology, Syracuse University, Syracuse, New York 13210; and 23 The Marine Biological Laboratory. Woods Hole, Massachusetts 02543. ABSTRACT The physiological ecology of the salt-marsh pulmonate gastropod, Melampus bidentatus Say, was investigated in specimens from the Little Sippewisset salt-marsh, Cape Cod, Massachusetts. M. bidentatus is tolerant of submergence, sur-viving 2-3 days at 20C and 14 days at 10C in 25%-100% seawater (SW). Snails acclimated at 10C tolerated temperatures of 32.2C-37.4C, and snails accli-mated at 20C tolerated 35.2C-40.7C, when submerged in 0%-100% SW. LD (T) 50 in air was 44.5C (10C acclimated) and 44.7C (20C acclimated). Aerial weight-specific O 2 consumption (VO 2 ) was 3-5 times higher than aquatic rates. Aerial and aquatic VO 2 was regulated (Q 10 < 1.5) over the ambient temperature range in both acclimation groups. The VO 2 of 10C acclimated individuals was lower than 20C acclimated specimens, a pattern of "reverse" acclimation asso-ciated with energy stores conservation. O 2 debt occurred after 5 h anoxia. In ad-dition, M. bidentatus compensates VO 2 for hypoxia by increasing both uptake rates and the degree of O 2 regulation of VO 2 during decreasing O 2 concentrations. M. bidentatus displays a ciradian rhythm associated with desiccation pressures, and thus VO 2 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 physio-logical adaptations required for terrestrial life, except for its aquatic egg-masses and planktonic development. INTRODUCTION Pulmonate snails of the genus Melampus live in the highest levels of the marine intertidal and are quite literally amphibious. Melampus bidentatus Say is found, often abundantly, in the higher levels of salt-marshes along the Atlantic coast of North America. In its reproductive activities, M. bidentatus is a primitive marine snail, spawning large numbers of small eggs which yield planktonic veliger larvae on hatching. Thus, all aspects of reproduction and early life-history have to be temporally "fitted" to the 2-week periodicity of spring tides (Russell-Hunter et al., 1972). In contrast, in its respiration, this species is a land snail breathing air though Received 28 May 1981; accepted 29 July 1981. Abbreviations: HCT, heat coma temperature; L:D, light:dark (ratio); LD(T) 50 , lethal dose (level) of temperature for 50% of experimental sample; MBL, Marine Biological Laboratory; SW, seawater; VO 2 , weight-specific O 2 consumption rate. 1 Supported by Grants GB-36757 and DEB-78-10190 from the National Science Foundation to W. D. Russell-Hunter; and by Research Grant 15-653 from Organized Research Funds of the University of Texas to R. F. McMahon. 246
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