Oxygen Minimum Zones - Eastern Tropical North Pacific and Gulf of Mexico
As part of a multi-year project (Grant 1151698) funded by NSF's Biological Oceanography program, our lab works collaboratively with biogeochemists to explore how oxygen depletion affects the diversity, distribution, and function of marine bacterioplankton. Our primary field site is the large, permanent oxygen minimum zone in the Eastern Tropical North Pacific (ETNP) off northern Mexico, although we have also worked in the ETSP off Chile and Peru. Dissolved oxygen concentrations in these OMZs fall from near saturation at the surface to below detection (< 50 nM) within the OMZ depths (~150-750 m). This steep gradient is coupled with similarly sharp transitions in nutrients, light, and other energy substrates. Microorganisms associated with OMZ gradients mediate key biogeochemical cycles through diverse metabolic processes, including nitrification, denitrification, anaerobic ammonia oxidation (annamox), and sulfur oxidation. Our lab is particularly interested in understanding the diversity and activity of OMZ sulfur- and nitrogen-utilizing bacteria across niches within OMZs (e.g., across depth zones, or between organic particle-associated or free-living microhabitats) and between OMZs with varying physical and geochemical conditions. To that end, we are also exploring microbial community diversity and function in regions with seasonal oxygen depletion and overall higher oxygen or nutrient concentrations, such as in the seasonally hypoxic (O2 < 20 uM) "deadzone" on the Louisiana Shelf. The following are from cruises to the ETNP OMZ (2013, 2014, 2017) and the Louisiana Shelf (2012, 2015).
Our lab studies the microbial communities (microbiomes) living in association with marine animals. The pictures below are from recent (Jan-Feb 2016, May-June 2017) trips to Moorea, French Polynesia to collect microbiomes from a wide diversity of reef fishes, crabs, corals, and algae. We hope to determine how animal-associated microbiomes relate to host phylogeny and ecological niche, as well as help shape host behavior and health. In 2016, roughly 300 fish spanning 14 families, 47 different species, and different developmental stages were collected and brought back to Georgia Tech for analysis of the microbiomes of the gills and lower intestine, with a primary focus on understanding the unique assemblages of the gill. We also collected environmental samples from the water column, sediments, multiple species of algae, and coral to identify possible vectors by which microbes colonize the reef fish microbiome. Most recently, in 2017, we also conducted experiments to determine how detoxification by the microbiome might allow certain species of crab to consume algae that produce noxious allelochemicals. These samples will provide a valuable resource for downstream metagenomic/metatranscriptomic analysis, sequencing of single amplified genomes (SAGs), microscopy, and isolation and culturing of key host-associated taxa. This work is supported by a generous grant from the Simons Foundation.
Our lab has recently established an exciting partnership with scientists at the Georgia Aquarium in Atlanta. Beginning in spring 2016, we have been sampling the microbial communities of the Aquarium's 6.5 million gallon Ocean Voyager exhibit on a (roughly) biweekly schedule. Our goal is to characterize the microbial metabolic processes that regulate nutrient cycling in this artificial system, and to compare these processes to those operating in the natural ocean. We also hope to better understand why and how the microbial community changes over time in the aquarium, potentially helping to manage the factors that cause periodic bacterial blooms that can compromise water clarity or animal health. The pictures below are from a recent sampling trip, to the ocean in downtown Atlanta!