Field and laboratory experiments on interference between Hydrobia totteni and llyanassa obsoleta (Gastropoda) and its possible relation to seasonal shifts in vertical mudflat zonation

Abstract

Laboratory and field experiments demonstrate that the mud snail Ilyanassa obsoleta strongly interferes with the smaller-sized Hydrobia totteni. Filter cages permitting free movement of H. totteni, but not I. obsoleta, demonstrate significant H. totteni emigration in the presence of I. obsoleta. In summer and early fall, when I. obsoleta is found in the low intertidal. H. totteni is confined to the upper intertidal and in the lowest intertidal where I. obsoleta is absent. In winter, when I. obsoleta migrates below mean low water, H. totteni abundance shifts downward. The interference effect observed with field and laboratory cages may underlie the seasonal H. totteni migration pattern.