Shell size variation in Littorina littorea in the western Scheldt estuary

Littorina littorea was collected along a salinity gradient in the Scheldt e stuary, located in the South of the Netherlands. Its morphological populati on structure was investigated to see whether salinity was correlated with s hell size and shell weight. Shell size did not increase along the salinity gradient, as was expected, but rather showed a clear size transition betwee n two salinity ranges (i.e., 10-20 parts per thousand, and 21-30 parts per thousand). Animals attain their largest size within a salinity range of 21- 30 parts per thousand. Relative shell weight did not vary consistently with salinity.