The Significance of Grain Size and Pore Water Content for the Interstitial Fauna of Sandy Beaches

The grain size distribution of four sandy beaches, three in the Baltic Sea and one at the Swedish West Coast, is described. A core sampler of new construction and giving successive subsamples of 10 or 20 cm3 is used to establish the horisontal, vertical and lateral distribution of grain size and grade of sorting for the four types of beaches. In a core with the total mean diameter of the grains of 500 jp the corresponding values of the subsamples may vary from 100 to 800 p. The lateral distribution in the beach is less heterogenous. Layers of quite different grain size may have the same grade of sorting just as well as a stratum of homogenous sand may contain adjacent subsamples of quite different sorting. The significance of these differences for the interstitial fauna is shown in choice experiments with the turbellarian Coelogynopora schulzii and the tubificid Aktedrilus monospermatecus. Representing two different modes of locomotion - creeping by means of cilia and burrowing by means of peristaltic movements of the whole body - they show no significant preference for graded sand fractions in the range