Environmental variance and dispersal explain benthic diatom spatial and temporal beta diversity in the Florida Everglades

Background/Question/Methods

Microbial communities drive ecosystem function and structure, but drivers of microbial community assembly remain largely unresolved. The metacommunity concept of communities linked by dispersal can be used to uncover both environmental and spatial factors correlated with microbial beta diversity. Since metacommunity dynamics operate on both spatial and temporal scales, adequate resolution at each level is needed to understand fully community assembly. Coastal wetlands are generally spatially structured and characterized by environmental gradients, making them useful settings for understanding the variable effects of environmental and dispersal factors on community assembly. This study investigated the spatiotemporal diversity of a benthic diatom metacommunity and associated explanatory factors – including hydrology and microbial community attributes – at opposite ends of a subsidy-stress gradient in the Florida Everglades using data from 16 sites over 8 years.

The Everglades is characterized by two major drainages transitioning from oligotrophic freshwater marsh to an oligohaline ecotone enriched with marine-derived phosphorus and salt. Benthic microbial mats pervasive throughout the Everglades enable detailed investigation into microbial metacommunity diversity across a gradient of increasing nutrients and salinity. We sought to determine and contrast freshwater and oligohaline environmental variance, spatial and temporal diatom beta diversities, and niche- and dispersal-based factors associated with those diversities using tests of homogeneity of dispersion, multivariate explanatory variable selection, and variation partitioning.

Results/Conclusions

Oligohaline communities were characterized by higher spatial but not temporal beta diversities than freshwater communities, 60% of which was explained by hydroperiod, water conductivity, and microbial mat total phosphorus. Environmental variables explained 32% of diatom spatial beta diversity in each freshwater and oligohaline regions: freshwater by microbial mat biovolume, oligohaline by water depth and mat organic content. Natural environmental variability was higher over both space and time in freshwater communities despite relatively equal environmental control with oligohaline communities. We postulate that dispersal limitation has a strong effect on freshwater diatom communities, while oligohaline diatom spatial beta diversity is less explained by dispersal and more by species interactive effects. Analysis of dispersal-based factors is ongoing and will help to resolve these hypotheses. This research sheds light on microbial metacommunity diversity along a subsidy-stress gradient in the Everglades with context of better understanding microbial community assembly in ecosystems at risk from anthropogenic and global climatic disturbances.