Assessing ecosystem responses of Gulf of Mexico coastal communities to ocean acidification using environmental DNA
Why we care
Recent efforts to monitor ocean acidification in the Gulf of Mexico via the Gulf of Mexico Ecosystems and Carbon Cycle (GOMECC) cruises have revealed spatial differences in ocean acidification. While we know that ocean acidification negatively impacts many species and exacerbates the effects of oxygen limitation and harmful algal blooms, there is little work to monitor or predict the effects of ocean acidification on biodiversity. This project employs cutting-edge technology using environmental DNA to assess biodiversity in different conditions in the Gulf of Mexico region.
What we are doing
Every organism sheds DNA. This project analyzes environmental DNA (eDNA), which is free-floating or microscopic DNA found in seawater, collected during the 4th GOMECC cruise, to identify biodiversity of bacteria, plankton, and fish in the Gulf of Mexico. eDNA will be compared to ocean properties to draw conclusions about drivers of biodiversity.
Benefits of our work
Links between eDNA, ocean acidification, and other ocean properties will provide a deeper understanding of environmental drivers of biodiversity. These relationships can inform predictions of biodiversity patterns and guide the management of key habitats in the Gulf of Mexico, and help us adapt to changing ocean conditions.
Ocean Acidification on a Crossroad: Enhanced Respiration, Upwelling, Increasing Atmospheric CO2, and their interactions in the northwestern Gulf of Mexico
Why we care
In the coastal ocean, local drivers such as nutrient input and physical oceanographic changes impact the magnitude of short-term variations and long-term trends in ocean acidification. The Gulf of Mexico’s coral reefs and banks are ecologically sensitive to changing ocean chemistry. Decadal acidification has been observed in the Northwestern Gulf of Mexico, linked more strongly to biological production of carbon dioxide than uptake of human-emitted carbon dioxide. Whether the observed acidification in this region represents a short-term phenomenon or a long-term trend is unknown. This project maintains critical ocean acidification monitoring in a region with impacted habitats and species.
What we are doing
This project will test the hypothesis that enhanced atmospheric carbon dioxide, nutrient input, and upwelling will cause the continental shelf-slope region in the Northwestern Gulf of Mexico to acidify faster than other tropical and subtropical seas. The research team will incorporate observations from new large-scale surveys into oceanographic and statistical models that predict variation in ocean acidification over space and time.
Benefits of our work
The outcomes of this project will meet the long-term goal of optimizing ocean acidification monitoring in the Northwestern Gulf of Mexico and will document methodology that can be used in similar efforts in the future. This project will examine an area in the poorly understood Gulf of Mexico Large Marine Ecosystem, produce the first ever high-resolution dataset in surface and subsurface waters, and direct the future deployment of in-situ monitoring devices in this ecologically and economically important region.
Among the NOAA designated Large Marine Ecosystems, the Gulf
of Mexico (GOM) remains poorly understood in terms of its current OA conditions, despite its
ecological and economic significance. In the northwestern GOM (nwGOM), decadal
acidification has been observed in the shelf-slope region, with metabolic production of CO2
contributing to a larger fraction of CO2 accumulation than uptake of anthropogenic CO2, and the
observed rate of acidification is significantly greater than that in other tropical and subtropical
areas. Unfortunately, whether the observed OA in this region represents a short-term
phenomenon or a long-term trend is unknown.
It is hypothesized that increasing atmospheric CO2, increasing terrestrial nutrient export
due to an enhanced hydrological cycle, and enhanced upwelling due to climate change will cause
the continental shelf-slope region in the nwGOM to acidify faster than other tropical and
subtropical seas. In order to test this hypothesis wave gliders, in -stiu sensor along withe underway measurements from research vessels will measure carbonated chemistry in in surface and shallow waters. Modeling will be used tp integrate the chemical signals into the models to hindcast/predict spatia; and temporal variation of the OA signal for the the optimization of monitoring design and implementation.
Humans have had a significant influence on estuaries through land use change and increased use of fertilizers, causing proliferation of algal blooms, hypoxia, and presence of harmful microbes. Now, acidification due to myriad processes has been identified as a potential threat to many estuaries. In Texas estuaries for example, short-term acidification as a result of episodic hypoxia is a well-documented phenomenon. Unfortunately, a longer-term trend toward chronic acidification (decreasing alkalinity, pH) has now been observed. The alkalinity decrease is likely caused by a reduction in riverine alkalinity export due to precipitation declines under drought conditions and freshwater diversions for human consumption.
Based on our existing long-term data, we hypothesize that hydrology acts as a switch, where increased river flows cause hypoxia and short-term acidification due to increased loads of organic matter, whereas prolonged low flows cause long-term acidification due to reduced loads of riverine alkalinity and calcification. In urbanized, wastewater-influenced systems, we hypothesize that reduced flows out of the watershed may lead to long-term acidification and chronic hypoxia due to reduced loads of riverine alkalinity and presence of low pH, high nutrient/organic matter wastewater.
To test our hypotheses, field and modeling studies are proposed to examine the relationships between estuarine acidification and other stressors (i.e., reduced freshwater inflow, hypoxia, and nutrient loading). Analysis of changes in ecosystem health and model calibration will be conducted based on long-term data. Mechanistic linkages between acidification, eutrophication and flow will be quantified through a field campaign. Chemical markers of organic matter sources fueling hypoxia will be determined. Future ecological states of the estuaries will be predicted using ecosystem models that account for projected changes in aforementioned parameters and ocean conditions based on IPCC estimates. The combination of prediction and consequence will be useful to multiple stakeholder groups.
This project will provide time-series observations of coastal ocean pH and carbon system properties, along with other variables that affect carbon transformations, in the northern Gulf of Mexico in support of goals elucidated in the NOAA Ocean and Great Lakes Acidification Research Implementation Plan. This project most directly addresses Theme 1: Develop the monitoring capacity to quantify and track ocean acidification in open-ocean, coastal, and Great Lake systems, but also addresses the educational objectives of Theme 6. USM will maintain a 3- m discus buoy in the northern Gulf of Mexico with a PMEL MAPCO2 system that includes a CTD, dissolved oxygen, and pH sensors. Meteorological sensors on the buoy will be utilized for computing air-sea fluxes of CO2. Water samples and continuous vertical profiles will be taken at the buoy site during quarterly cruises. Water samples will be analyzed for DIC, TA, pH, dO, S, NUTS and chlorophyll a. Analyzed water samples and profile data will be submitted to NODC through standard NOAA OAP submission spreadsheets containing both data and associated metadata.
While this work is focused on the Gulf of Mexico additional time-series sites in the South Atlantic Bight and Gulf of Maine can provide a comparison over a wide range of coastal and latitudinal regimes. The northern Gulf of Mexico, Florida and South Atlantic Bight regions are all commonly influenced by one contiguous western boundary current system, which originates with the Loop Current in the Gulf of Mexico and then becomes the Gulf Stream along the southeastern U.S. continental shelf. The Gulf of Mexico observations will be compared with the other western boundary current influenced site in the South Atlantic Bight maintained by the University of Georgia (UGA) and the high latitude site in the Gulf of Maine maintained by the University of New Hampshire (UNH).