The external layers of marine organisms are often covered in biofilms comprised of rich microbial communities that can act as a boundary layer through which the environment and biotic interactions the host experiences are modified. However, host-microbe interactions and the importance of biofilm microbial communities to the overall health of the host are generally poorly understood. This is especially true of the relationship between seagrass blades and their associated microbial communities. This study characterized the microbial communities associated with Thalassia testudinum (turtle grass) blades at five sites along a gradient of freshwater influence to correlate changes in community composition with abiotic and host conditions. Microbial samples were taken at each site from the blade biofilm and surrounding water column during three sampling events (Jun-Sept 2016) as well as once post-Hurricane Irma (September 2017). At each sampling, environmental parameters were measured and seagrass tissue was collected for nutrient composition. Seagrass surveys were also conducted during the study to characterize host condition at each site. All microbial samples were analyzed using 16S rRNA gene sequencing and the QIIME2 pipeline with amplicon sequence variants (ASVs) to obtain bacterial and archaeal composition and diversity.
Results/Conclusions
A total of 12,231 ASVs, or microbial species, were found in the biofilm and water microbial communities across all samples. Biofilm samples (BF, n=52) contained the greatest number of ASVs (11,348) dominated by members of the Proteobacteria, Planctomycetes, and Cyanobacteria phyla. At all five sites, the composition of the biofilm community was significantly different from that of the water column (W, n=15) with the two sample types only sharing 2% (244 ASVs) of microbial species. Biofilm communities also exhibited higher species diversity on average than the water column communities (BF- 8.65, W-5.73; Shannon Index). Within the biofilm communities, compositional changes significantly correlated with changes in abiotic conditions, including water depth and salinity, as well as host characteristics, including seagrass growth rates and nutrient composition. Additionally, 21 ASVs were present in 100% of the biofilm samples from all sites and sampling events which may comprise a core microbial community unique to T. testudinum plants. This study lays the foundation for experiments to directly test the effect of abiotic stress and host condition on the composition of these microbial communities and to ask how those compositional changes within the biofilm relate to overall seagrass health.