USING BENTHIC FORAMINIFERA TO CREATE A DECADAL-SCALE COMPARISON OF
ECOLOGICAL STATUS THROUGHOUT THE NORTHERN GULF OF MEXICO

The Deepwater Horizon (DWH) Oil Spill released over 6 million liters of oil into the northern Gulf of Mexico (nGOM) from April to July of 2010. The event led to economic decline as the nGoM provides valuable services through fisheries and tourism. Although most of the oil has been degraded through natural processes, hydrocarbons remain stored in sediments and have lasting effects on benthic communities, such as foraminiferal populations. Benthic foraminifera, single-celled protists that live in seafloor sediment, are used as bioindicators of health because of their high diversity and abundance throughout the world's oceans, preservation of their shells (tests), and their short life span. Since the DWH oil spill, abundance and diversity data have been recorded across seven time-series locations in the nGoM, at water depths spanning 400 to 1600 meters. In 2021, an application of this data was used to calculate the AZTI Marine Biotic Index (AMBI) for benthic foraminifera (f-AMBI) in the nGoM. AMBI groups species based on their sensitivity to organic enrichment in the environment and calculates a quantitative value to represent the Ecological Quality Status (EcoQS) of a location. The original calibration determined f-AMBI values in 2015. This project establishes a decade-long f-AMBI dataset across the nGoM and compares EcoQS across the seafloor. A recalibration was performed to ensure the validity of f-AMBI over a decadal scale. After validating the calibration, f-AMBI values were calculated and evaluated to understand EcoQS changes across the nGoM from 2015 to 2025. This is the first application of f-AMBI on a decadal scale, and this study assesses how f-AMBI can be used as a long-term benthic health monitoring tool. Consistent polluted levels close to the DWH wellhead indicate lasting effects from the oil spill on community health even fifteen years after initial impacts. Individual patterns in EcoQS were observed at each time series site, indicating there are multiple environmental stressors affecting sites across the nGoM (ie, storms and Mississippi River discharge). This study contributes to a larger effort to understand the natural variability of the nGOM and provides information that will help identify targets for future management efforts. 

This project is part of a greater effort at Eckerd College, called Scientists-at-Sea, with the intention of training research geologists while researching the impacts of the Deepwater Horizon Oil Spill. For more information on our 2023 program, please visit: https://scientistatsea23.eckerd.edu/home 

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