Seagrasses occur in coastal waters worldwide and are critical habitats for a variety of species from algal epiphytes to manatees, yet little is known about the microbial communities associated with seagrass blades and the interactions these communities have with their seagrass host. This study examines microbial community composition and diversity on Thalassia testudinum (turtle grass) blades in order to correlate community changes with host and environmental conditions. Five sites were established extending ~2 miles offshore, where salinity increases with distance (22-29 ppt), but water depth is greatest at intermediate distances (1.64, 1.88, and 2.21 m) and shallowest at near and far sites (0.98 and 1.23 m). Microbial samples were taken at each site from blade biofilm, corresponding blade tissue, and the water column during three sampling events over the course of the summer months (June-September 2016). At each sampling, environmental parameters were also measured and seagrass tissue was collected for nutrient composition (C:N:P, δ13C, and δ15N). Seagrass surveys were also conducted during the study period in order to characterize environmental and host condition at each site. All microbial samples were analyzed using 16S rRNA gene sequencing on an Illumina MiSeq in order to obtain bacterial and archaeal composition and diversity.
Results/Conclusions
Freshwater input as well as water depth appear to be important drivers for other environmental parameters and host condition at each site. Average blade length had a positive correlation with average depth by site with a 0.17 centimeter increase for every centimeter in depth (R2=0.66). Blade growth rates were higher at the deeper sites (0.61, 0.79, and 0.82 cm/day) and lowest at the shallow sites (0.54 and 0.53 cm/day). Mean percent cover of T. testudinum did not follow this trend with highest cover at the far site (89.7% ± 8.49 S.E.) and lowest cover at the near site (43.8% ± 10.68 S.E.) indicating depth and freshwater input both influence seagrass abundance and growth. Microbial samples from biofilm and blade tissue were compared with water column samples to see if they significantly differed. Microbial community composition from blade and biofilm tissue were also then correlated with environmental and host parameters to explain variation within the community. This study will help to understand plant-microbe interactions, as well as how effects of abiotic stressors on microbial community composition may influence the health and success of the seagrass host.