Effect of acute exposure to low environmental calcium on respiration and locomotion in Lymnaea stagnalis (L.)

Environmental calcium is a major factor affecting the distribution of freshwater gastropods. Whilst the effects on growth and morphology are fairly well understood, little is known about how calcium availability affects other aspects of gastropod biology. Lymnaea stagnalis (L.) is considered a calciphile and exhibits reduced growth and survival in environments containing less than 20 mg l(-1) Ca(2+). Many freshwater systems exhibit fluctuations in calcium concentration over time: where calcium levels are normally high there may be periods of low [Ca(2+)], for example following periods of flooding. Here we examined the effects of acute periods of low (20 mg l(-1)) environmental calcium on the physiology and behaviour of L. stagnalis, specifically measuring how locomotion and respiration differ between high calcium (80 mg l(-1)) and low calcium (20 mg l(-1)) environments. We found that in a low calcium environment crawling speed is reduced, and that this coincides with an increase in cutaneous respiration, indicating that the increased metabolic demands of calcium acquisition at low [Ca(2+)] reduce the energy available for locomotion. Conversely we found a decrease in aerial respiration in hypoxic conditions in the low calcium relative to the high calcium environment. In conclusion, we found that acute exposure to low environmental calcium has a highly significant effect on locomotion and respiration, which may have consequences for snail fitness when no morphological effects are apparent.