Strategies of post-larval dispersal in non-tidal soft-sediment communities

Abstract

Considering the relative significance of different dispersal rates and strategies is key for a better understanding of the scale and potential thresholds of benthic recovery processes. Despite our increased understanding of post-larval dispersal in tidal areas, our knowledge of post-larval dispersal potential is very limited for non-tidal systems, for example in the Baltic Sea, where dispersal has not previously been quantified in soft-sediment communities. For non-tidal systems the absence of regular tidal-mediated currents would suggest that post-larval dispersal potential might be limited. In this study a combination of traps was used to quantify post-larval dispersal across a wind exposure gradient in a non-tidal system. Traps allowed for a comparison of species either emerging from the sediment, being transported in sediment bedload, being transported in the water column or settling from the water column. Results from this study provide the first evidence that also in the Baltic Sea, a non-tidal system, benthic species disperse in relative proportions distinctly different from the relative composition of the resident community. A variety of post-larval dispersal strategies with species-specific differences were observed. Dispersal in the water-column might be comparatively less important in the Baltic Sea where tidal currents are absent. The majority of epifaunal species represented in the ambient community were also recorded within all dispersal modes, whereas infaunal species were less common. This suggests that, in the absence of regular tides, infaunal dispersal may be more stochastic and dependent on wind-induced waves and currents exceeding a long-term average. Post-larval dispersal was also found to be modified by the local hydrodynamic regime. Our results highlight the importance of different post-larval dispersal strategies for connectivity in soft-sediment communities in non-tidal systems.