Anisotropic clumped (patchy) dispersal of species is a widespread phenomenon in nature, however, its relevance for structuring communities and maintaining biodiversity is still a matter of debate. We used a spatially explicit simulation model to assess the effects of spatial aggregation through this dispersal strategy compared to isotropic clumped (local) dispersal on the diversity of a model community of sessile species. The species differed only in terms of their dispersal distance and no a priori trade-offs between dispersal and local competitive strength were assumed. We investigated spatially homogeneous and heterogeneous environments without and with temporally fluctuating reproduction success. In all cases patchy dispersal allowed the long-term coexistence of a variety of species—in contrast to local dispersal. In particular, patchy dispersal was found to decouple the mechanism of spatial aggregation from the dispersal distance. This supports species coexistence even in environments where local dispersal was a superior or inferior dispersal strategy. Thus, the specific way of spatial aggregation can be decisive for coexistence. Spatial aggregation independent of the dispersal distance is an attribute of dispersal offering new possibilities for trade-offs with life-history traits and with the dispersal distance itself.

Very few details exists concerning the dispersal traits of Antarctic species and dispersal distances in particular are mostly unknown. Especially the general low number of mesoplanktonic larvae has caught attention, leading to the formulation of Thorson’s rule. From this concept, originally concerning only trophic aspects, sometimes a reduced dispersal distance is deduced. Using a generic simulation model we show that in a benthic habitat exposed to iceberg scouring, even short dispersal phases of few hours are sufficient for a pioneer species to persist. This is very surprising for a pioneer species which should be able to disperse widely and colonise distant disturbed areas which are free of superior competitors. Our model revealed that the reason for this is the non-linear dependence of the dispersal distance on the disturbance regime and on species longevity. Thus, it is the combined effect of life history and disturbance traits which is important here: a sufficiently high disturbance frequency due to iceberg scouring and a long individual lifetime due to the low temperature decrease minimum dispersal distances required for persistence and thus coexistence and present an additional explanation for the relative rarity of planktonic larvae.

Mega-epibenthic diversity was analysed using a seabed photography at four stations off Bouvet Island and one station at the Spiess Seamount in the South Atlantic. Surprisingly, the intermediate-scale diversity within the area of investigation was not lower compared to that on the Patagonian shelf and only moderately lower than that on the Antarctic continental shelf. This result is incompatible with Mac Arthur and Wilson's Island Biogeography Theory describing species richness as a function of immigration of new species into an area and its extension. The relatively high species number and the very small extension of the Bouvet shelf compared to the much larger continental shelves of the other two areas can be explained by long-range dispersal of marine benthic animals in the Antarctic Circumpolar Current and high habitat heterogeneity. The observed uncoupling of intermediate-scale from large-scale background species diversity on the Antarctic shelf raises the question whether in these benthic systems an upper capacity limit for diversity exists.