Associations between shell strength, shell morphology and heavy metals in the land snail Cepaea nemoralis (Gastropoda, Helicidae)

In snails there is an intimate relation between shell size, thickness, strength and calcium content that may be influenced by environmental factors such as predation and heavy metal pollution. The snail Cepaea nemoralis shows variability for shell colour and banding pattern, and frequencies of colour morphs are highly variable in natural populations. We used C. nemoralis to investigate (i) the relations between shell morphology, shell Ca and heavy metal content (Cd, Cr, Pb, Zn), and shell strength, (ii) differences in shell morphology and shell strength among localities and yellow and pink shells and (iii) whether snails from polluted sites show increased levels of heavy metals in their shell. Larger shells were heavier, thicker, needed a higher force to be crushed but did not have a higher Ca concentration. Cd and Zn concentrations were higher in shells from polluted plots compared to shells from unpolluted plots but Ca levels in the shell were comparable among plots. Zn concentration was negatively correlated with shell traits. Although there was substantial variation in shell strength, thickness and dry weight among localities, none of the shell traits differed between individuals from polluted and reference plots nor between colour morphs. Our results suggest that the effect of heavy metal pollution on shell strength and morphology is limited in the investigated populations.