Life in the intertidal zone is harsh. As soon as the tide retreats, shore-dwelling species are deprived of food and exposed to potentially life-threatening temperatures, so conserving their energy is probably at a premium. David Marshall from the Universiti Brunei Darussalam and an international team of collaborators suspected that instead of allowing their metabolism to escalate as temperatures rise – like most land-based cold-blooded animals (ectotherms) – shore-dwelling ectotherms might have chosen to conserve resources by reducing their metabolism when environmental temperatures escalate, until the cooling sea returns, when they can begin foraging again (p. 3649).
Collecting Echinolittorina malaccana snails from the Hong Kong and Brunei Darussalam coasts, the team measured the molluscs' resting metabolic rate and found that instead of increasing as the mercury rose, it remained almost constant between 35 and 46°C: they were conserving energy. The team also saw that the snails stopped crawling around at 41.5°C and went into a heat coma at 46°C, which is the temperature that activated the snails' protective, but costly, heatshock response. Finally, as the team turned the thermostat up higher, the snails' resting metabolic rate rocketed as they ramped up their heat shock response to combat the heat.
So E. malaccana snails have become thermally insensitive from 35 to 46°C, when they maintain a stable resting metabolism. The team points out that this strategy is extremely successful as the temperature that the snails experience naturally in their habitat rarely exceeds 46°C, allowing them to conserve energy rather than fritter it away when resources are scarce.