Disentangling the effects of dispersal and salinity on beta diversity in estuarine benthic invertebrate assemblages


Correspondence: Alf B. Josefson, Department of Bioscience, Aarhus University, Frederiksborgvej 399, 4000-Roskilde, Denmark.

E-mail: aj@dmu.dk



The identification of sources of beta diversity, the turnover component of diversity, is important to understand the generation of diversity, and thus central to biodiversity and biogeography. We investigated the relative importance of environmental filtering and dispersal-based factors affecting beta diversity in benthic macroinvertebrate assemblages at different spatial scales in an estuary, and tested the hypothesis that species with a long pelagic larval life are more dispersive and have lower beta diversity than species with direct benthic development.


Denmark, the North Sea–Baltic Sea transition area.


Additive partitioning of alpha diversity computed with multiplicative beta diversity was performed on species abundance of 279 species using 330 samples from 110 sites at four hierarchically arranged spatial scales where the largest scale comprised regions (> 100 km) with different salinity regimes, each subdivided into two sediment habitats. Pairwise beta diversity between sites was examined across environmental gradients and by distance decay functions within areas with more homogeneous environments.


Beta diversity was high among regions and among sites within habitats, but low between habitats. Abundance–occupancy relationships suggested that species with a long pelagic life were more dispersive than species with direct benthic development. Beta between sites in the two dispersal groups changed at the same rate with salinity difference among regions, but showed different rates of geographical distance decay among sites within regions. Average beta diversity and decay rates were higher, and halving distances were shorter for the less dispersive species.

Main conclusions

Different beta diversity of species groups with different propagule vagility suggest that beta diversity is negatively related to dispersivity. With the environmental filtering factor salinity as the overriding factor at the regional scale (> 100 km), and restrictions on dispersal affecting beta diversity at smaller scales, results show that the relative importance of niche-based and dispersal-based factors changes with scale.