Pelagic microbial community dynamics in northern Gulf of Mexico

Background/Question/Methods: The Gulf of Mexico (GOM) is a dynamic ecosystem influenced multiple natural and anthropogenic processes that can greatly alter environmental conditions.  This ecosystem is effected by GOM loop current dynamics that brings warm nutrient-poor water from the Caribbean, freshwater input by the Mississippi river, natural seeps of hydrocarbons from the ocean floor, and more recently, anthropogenic influences of the Deepwater Horizon oil spill and eutrophication due to agriculture along the Mississippi river basin.   Microbial communities form the base of complex food webs in the GOM, but we know little about how these communities vary in response to these naturally occurring fluctuations in environmental conditions, as well as in response to anthropogenic disturbances.   As part of the Gulf of Mexico Research initiative funded DEEPEND consortium, the current study is investigating spatial and temporal variation in microbial community at different depths across a stratified sampling grid in the northern GOM.  Seawater samples were collected on biannual cruises at five sites in cruise 1 and eleven sites during cruise 2.  Seawater samples were collected at four depths representing distinct pelagic zones. Next-generation sequencing on an Illumina MiSeq was used to capture the microbiome of from each sample.  Analysis of microbial community diversity and composition was conducted to assess spatial, temporal, and depth variation among samples as well as how these patterns are related to broader oceanographic features at the time of collection.  

Results/Conclusions: This study will help establish an important baseline regarding natural fluctuations in microbial communities across these different environmental influences.   Initial results indicate that microbial communities were highly variable among sampling sites for both cruises, but no clear geographic patterns emerged.  Depth was a major factor influencing diversity and composition of microbial communities.  Microbial composition displayed clear depth stratification between photic and aphotic zones.   Differences among depths were driven in part by increased abundance of Cyanobacteria at the photic depths, and higher abundance of Crenarcheota at aphotic depths. Samples collected during cruise 1, which occurred during spring months, showed higher overall microbial diversity compared to samples from cruise 2 during late summer months.  Ongoing analysis is focused on relating these observed patterns of microbial diversity and composition to oceanographic features such as water nutrient chemistry, chlorophyll a concentration, temperature, mega fauna abundance, and ocean current patterns.  Combining these data will allow for a more complete image of what factors are controlling these essential communities in the GOM.