The effects of the gastropod Terebralia palustris on infaunal communities in a tropical tidal mud-flat in East Africa

The gastropod Terebralia palustris (Linnaeus) is one of the largest prosobranchs found in tropical intertidal habitats. The adults form feeding aggregations and frequently dominate the surface of muddy substrates, where they clearly destabilize the sediment surface. We tested the following hypotheses: 1. The gastropod has negative effects on the density of infaunal animals because of potential food competition and/or surface sediment disturbance. 2. The disturbance exerted by T. palustris results in more variable infaunal assemblages, especially where intensity of disturbance is high. To address these hypotheses gastropods were either enclosed or excluded from experimental cages, which were randomly assigned to blocks as far as 300 m apart on an intertidal mudflat in East Africa. After nine weeks of enclosure the gastropod at high densities clearly affected the meiofauna assemblages. Several meiofauna groups were found in significantly reduced densities in the presence of the gastropod compared with control cages without the gastropods, supporting our primary hypothesis. In cages without T. palustris a cyanobacterial carpet developed while this was not evident in enclosure cages. T. palustris had no significant impact on the macrofauna assemblage. In support of our second hypothesis, multidimensional scaling ordination (MDS) suggested that there was an increased variability of meiofauna within cages with high density of T. palustris.