Mesoscale spatial structures of soft-bottom macrozoobenthos communities: effects of physical control and impoverishment

The recognition of the nature of spatial and temporal variability within ecosystems is crucial for understanding the processes that maintain species diversity and ecological stability. In the present study, mesoscale spatial structures of soft-bottom macrobenthic communities were explored at sites with contrasting disturbance regimes and benthic diversities. Two sites in a glacial Arctic fjord were selected: the Inner site, where sediments are inhabited by an impoverished community composed of a few species resistant to large-scale, chronic physical disturbance by glacial sedimentation, and the Outer site, where diverse fauna is structured by biological interactions among populations of species of different sizes and functional groups. Samples were taken at 6 stations (4 van Veen grabs collected per station) located along a 1 km transect separated by 0 (samples collected at the same station), 200, 400, 600, 800, and 1000 m. Spatial variation at the Inner site was apparent only in changes in relative abundances among a few numerically dominant species (explored using untransformed data), and the fauna was homogenous with respect to species composition (based on presence/absence data). The spatial heterogeneity in the Outer site community was evident both in species composition and in relative abundances of dominant species populations. The significant autocorrelation peaks on a correlogram of Bray-Curtis similarities of untransformed data indicated a successive sequence of homogenous patches of a minimum 200 m radius, separated by 600 m. Spatial patterns of species composition similarity varied among species groups of different mobility: sedentary fauna did not exhibit a mesoscale patchiness, while clear patchiness was documented for motile and discretely motile organisms. The current study demonstrates that the spatial structure of benthic biota is related to the diversity and the perturbation level of the studied communities. It also supports the recommendation for spatial separation of replicate samples in soft-bottom macrobenthic surveys.