Marine succession: The effect of two deposit-feeding gastropod species on the population growth of Paranais litoralis Müller 1784 (oligochaeta)

Abstract

The hypothesis that persistent populations of the mud snails Hydrobia totteni Morrison and llyanassa obsoleta Say in salt marsh mud flats affect the population growth of a more ephemeral oligochaete, Paranais litoralis Müller is tested. Using experimental microcosms, we demonstrate that both snail species affect negatively the rate of population increase of the oligochaete. For Hydrobia, oligochaete population density eventually reaches the same approximate maximum, irrespective of snail density. This may relate to the penetration by worms of initially anoxic deeper sediments. For llyanassa, maximum population density is depressed with increasing snail density, which may relate to the complete sediment disruption caused by the latter snail species. Staggered cycles of population increase and decrease with changing snail density would make a consistent density effect nearly impossible to identify in normal field sampling. However, our results suggest that persistent snail populations may explain the relative rarity of polychaete population explosions in mud flats, except when the local persistent biota has been wiped out via disturbance or predation.