Mangroves can accumulate as much as several meters of peat in their marine sediments. The amount of peat is variable and may relate to abiotic coastline features, mangrove species, peat microbial communities, or a combination of factors. We investigated the microbial correlation with four mangrove sites that differed in their mix of mangrove species, as well as their topography and slopes. At each site we used a Russian peat corer to collect samples of peat and sediment until refusal. The depth to refusal varied from one meter to three meters. Samples were taken from two separate locations on Isla San José, one on Isla Espiritu, and one on a mainland Mexico beach called El Mérito, located not far from La Paz. Core samples were collected for both microbial community analysis in 5 cm segments every 20 cm. Samples were frozen within 6 hours, and transported frozen to the lab. The soil whole DNA was extracted using MoBio PowerLyzer PowerSoil kits. These DNA extracts were used to sequence the v3 and v4 region of the 16S rRNA gene on the Illumina MiSeq, and bioinformatics analysis was performed using Quantitative Insights Into Microbial Ecology (QIIME) protocols and workflows.
We found that bacterial and archaeal communities varied predictably with depth; microbial communities at a given depth from one core more closely resembled microbial communities from the same depth of a different core than they did the other depths within the same core. Further, based on visual characterization, the microbial communities in samples with high root content clustered together, as did the microbial communities in clayey samples. Characterizing the microbial communities associated with mangrove sediments and peat represents the first step in understanding the role microorganisms play in mangrove peat accumulation. These data indicate that the microbial communities are distinct in peat at depth, and that these communities are consistent across mangroves in this area. As sea level rises, mangroves are threatened if they cannot increase elevation via peat or sediment accumulation. Future work will investigate whether microorganisms in the deep peat are retarding carbon turnover and allowing for peat accumulation.