Seasonal changes in the freezing tolerance of the intertidal pulmonate gastropod Melampus bidentatus Say

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Abstract
The mean lethal temperature of Melampus bidentatus Say ranged from −5 °C in July to −13 °C in December. The percentage of tissue water frozen measured at the mean lethal temperatures was 3% for snails collected in the summer and 74.9% for snails collected in the winter. The supercooling point of the whole snails ranged from −9 °C in September to −6.4 °C in February. The presence of an ice nucleator is indicated by an increase in the supercooling point of the haemolymph from −11.5 °C in the fall to −7.5 °C in the winter. Water content in the snails varied from 2.6 mg water/mg dry weight to 3.6 mg water/mg dry weight; however, there was no correlation between low water contents and an increase in freezing tolerance. Whole animal glycerol contents ranged from 1.14 to 2.96 μmol/g fresh weight and proline contents ranged from 1.20 to 2.19 μmol/g fresh weight. Sorbitol and trehalose were not detected.