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

The gastropod Terebralia palustris (Linnaeus) isone of the largest prosobranchs found in tropical intertidal habitats. Theadults form feeding aggregations and frequently dominate the surface of muddysubstrates, where they clearly destabilize the sediment surface. We tested thefollowing hypotheses: 1. The gastropod has negative effects on the density ofinfaunal animals because of potential food competition and/or surface sedimentdisturbance. 2. The disturbance exerted by T. palustrisresults in more variable infaunal assemblages, especially where intensity ofdisturbance is high. To address these hypotheses gastropods were eitherenclosedor excluded from experimental cages, which were randomly assigned to blocks asfar as 300 m apart on an intertidal mudflat in East Africa. Afternine weeks of enclosure the gastropod at high densities clearly affected themeiofauna assemblages. Several meiofauna groups were found in significantlyreduced densities in the presence of the gastropod compared with control cageswithout the gastropods, supporting our primary hypothesis. In cages withoutT. palustris a cyanobacterial carpet developed while thiswas not evident in enclosure cages. T. palustris had nosignificant impact on the macrofauna assemblage. In support of our secondhypothesis, multidimensional scaling ordination (MDS) suggested that there wasan increased variability of meiofauna within cages with high density ofT. palustris.