Salinity Tolerances Of Some Common Prosobranchs

Abstract

The abundance of gastropods characteristic of rocky shores throughout the world (Southward, 1958) has encouraged investigation of their ecology and behaviour in several areas, although studies under laboratory conditions seem to have been restricted largely to the common European species Littorina littorea and Patella vulgata. Most investigations of littorinid behaviour have concentrated upon their response to light and gravity (see Newell, 1958, for a critique of earlier work), as the most important factors, after exposure, to influence life upon the shore. Variations in salinity are also significant, however, and ecological observations make it clear that littorinids are able to withstand a considerable range of salinity (Moore, 1958; Fretter & Graham, 1962; Newell, 1964; Green, 1968). But ecological studies alone do not necessarily reveal whether this capacity is to resist an adverse environment by a period of inactivity or, more particularly, to retain activity within a wide salinity range; nor do they show how far the potentialities of particular populations are related to the conditions under which they actually live. Examination of this aspect has been undertaken with L.littorea on the Atlantic coast of Canada (Gowanloch & Hayes, 1927) and with L.knysnaensis Philippi and other prosobranchs in False Bay, South Africa (Broekhuysen, 1940). However, these studies were restricted to determination of limiting salinities, without consideration of the extent to which activity occurred within the range of tolerance of the species concerned. Investigation of salinity tolerances in L.littorea is also of some general interest since, as pointed out by Newell (1958), the behaviour pattern of this species is probably fairly typical of the more mobile intertidal invertebrates.