Evidence for dispersal and habitat controls on pond diatom communities from the McMurdo Sound Region of Antarctica

Abstract

Microbial life flourishes in the ponds of the McMurdo Sound Region, which includes the McMurdo Dry Valleys (MDV) and the exposed coastal areas of Ross Island, Antarctica. Diatoms live within resident microbial mats, and because of the simplified trophic structure and limited dispersal vectors, the McMurdo Sound Region is an ideal locality to investigate diatom community assembly processes. Wind is hypothesized to transport microbiota between habitats, and following the species-sorting perspective, local conditions should act as an environmental filter. However, the role of spatial scale versus habitat characteristics on diatom community structure has not been investigated. To gain insight into these processes, we sampled microbial mats from 25 ponds and used variation partitioning to assess the spatial scales at which diatoms were influenced by chemistry and physical variables. We found substantial spatial structure in diatom communities, and spatial scale explained more variability than environmental variables. No diatoms were exclusive to Ross Island, but some species were only found in the MDVs. Furthermore, diatom communities were more likely to resemble those from other nearby ponds rather than distant ones, regardless of environmental conditions. Of the environmental variables, bromide and chloride (both indicators of marine influence) were among the most important. These results suggest that geography, dispersal, and historical environmental conditions play a major role in structuring diatom communities at large spatial scales, and chemistry may be more important within regions. These results help explain the biogeography of diatoms here and elsewhere and expand our knowledge of mechanisms influencing microbial metacommunity structure.