Microbial communities in the Guana Tolomato Matanzas National Estuarine Research Reserve: An assessment of the responses of Spartina alterniflora Epiphytes to nitrogen enrichment, and a characterization of benthic cyanobacterial diversity

Abstract

Elevated nitrogen and phosphorus inputs from anthropogenic sources, which can lead to significant increases in algal biomass and changes in algal community composition, poses a serious threat to estuarine ecosystems worldwide. While numerous studies have addressed the impacts of nutrient enrichment on epiphytic algae in seagrass habitats, few have investigated potential nutrient-driven changes to epiphytes on emergent salt marsh plants, such as Spartina alterniflora. Epiphytic microalgae on S. alterniflora play an important role in food availability in salt marsh ecosystems, and epiphytic nitrogen-fixing cyanobacteria also provide an important source of nitrogen for salt marsh consumers. The first study included in this work employed DNA metabarcoding to analyze the impacts of sediment nitrogen enrichment on epiphytic cyanobacteria, diatoms, and prokaryotes (bacteria and archaea) on S. alterniflora in the Guana Tolomato Matanzas National Estuarine Research Reserve (GTMNERR) in northeastern Florida (USA). Nitrogen enrichment resulted in significantly lower alpha diversity of epiphytic cyanobacteria, suggesting that anthropogenic nitrogen input may have consequences for these important diazotrophic communities. Analyses of epiphytic beta diversity also indicated that many taxa within these microbial communities may exhibit habitat specificity. The second study included in this work consisted of a culture-based characterization of benthic intertidal cyanobacteria isolated from GTMNERR. Cyanobacteria often dominate benthic algal assemblages in intertidal ecosystems. In these environments, cyanobacteria provide a number of important ecosystem services, including sediment stabilization. Relatively little effort has been made to characterize benthic cyanobacterial diversity in sub-tropical estuarine ecosystems, however. In this study, sixteen strains of benthic cyanobacteria from the GTMNERR were isolated and characterized using a polyphasic approach. Two novel species were formally described in this study. An additional six novel species, and two novel genera, were tentatively identified, indicating that intertidal habitats such as the one studied here represent an untapped wealth of novel cyanobacterial diversity