Rates of post-larval bedload dispersal in a non-tidal soft-sediment system

Quantifying rates of dispersal and understanding patterns of colonization are key for predicting disturbance-recovery dynamics. For soft-sediment benthic communities recruitment is not restricted to one single event, but can be highly variable on several spatial and temporal scales. To investigate the temporal persistence of post-larval bedload transport in a non-tidal system, field experiments were conducted at 4 sites (5 m depth) across a wind-wave exposure gradient over 2 summers. Results indicate that bedload dispersal is temporally variable and dependent on an interaction between species-specific characteristics (including seasonal peaks in reproduction), site-specific hydrographic conditions, grain size characteristics and transport of sediments and drift algae. Dispersal of more passive taxa (Ostracoda, juvenile gastropods, Macoma balthica) was found to be associated with higher rates of sediment and algal transport, while more active species (Hydrobia ulvae and Potamopyrgus antipodarum) dispersed relatively more at sheltered sites. At higher rates of sediment transport, there was an increase in the proportion of larger M. balthica individuals dispersing, in contrast to Hydrobiidae, which had an increased proportion of smaller individuals. Our study suggests that frequent post-larval dispersal plays a central role in the population dynamics of many benthic invertebrates, in non-tidal systems. While the distribution of species is heavily influenced by peaked larval recruitment over large spatial scales, the net result of continuous small-scale dispersal events is clearly important and may contribute to the resilience of benthic communities.