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Holding your breath for hypoxia monitoring tools? Applying M-AMBI in a northern Gulf of Mexico estuary
Citation:
Paul, J., J. Nestlerode, AND B. Jarvis. Holding your breath for hypoxia monitoring tools? Applying M-AMBI in a northern Gulf of Mexico estuary. 27th Biennial Coastal and Estuarine Research Federation (CERF) Conference, Portland, OR, November 12 - 16, 2023.
Impact/Purpose:
We present an evaluation of the response of a benthic habitat condition index, M-AMBI, to various dissolved oxygen levels over multiple time scales in the Pensacola Bay estuary. Our analysis indicates that evaluating M-AMBI results in the context of eutrophication related stressors (i.e. low oxygen and hypoxia) may be significantly improved when paired with targeted high frequency monitoring of water quality conditions. This presentation should be of interest to scientists and managers, including those from across the Gulf of Mexico region, concerned with monitoring and management of estuarine habitats as it may inform the future use and application of taxonomic-based benthic indicators and water quality monitoring tools for describing ecosystem condition. This invited presentation will be given as part of a special session ("Ode to Benthos") at the 27th Biennial Coastal and Estuarine Research Federation (CERF) conference in Portland, Oregon, 12-16 November 2023.
Description:
The multivariate AMBI (M-AMBI) is an extension of the AZTI marine biotic index and is used to grade benthic habitat condition. It was adapted to the United States and adopted by the U.S. Environmental Protection Agency for monitoring coastal ecosystems at the national level, replacing individual regional indices that were not directly comparable with each other. Yet, application in Gulf of Mexico coastal estuaries has been limited and requires further validation at smaller scales. M-AMBI is calculated from abundance weighted tolerances of benthic fauna to organic enrichment, however, sensitivity of the index to intermittent hypoxia (dissolved oxygen [DO] ≤ 2 mg l-1), a common stressor in the northern Gulf, is unclear due to few mechanistic studies. As such, our objectives were to apply M-AMBI in a northern Gulf of Mexico estuary, Pensacola Bay, where salinity stratification occurs seasonally, and examine index response to DO conditions over the previous 1, 2, 7, 14, and 31 days including minimum, maximum, mean, and hours below 5, 2, 1, and 0.5 mg/L. No significant associations were observed between index score and DO at the time of sampling or in the days immediately prior to sampling. The strongest relationships observed were the number of hours over the previous 2 weeks to one-month where concentrations dipped below 5 and 2 mg/L, supported by linear regressions and fitting DO conditions to a NMDS ordination of benthic community abundances. A random forest model was used to evaluate relative importance of DO, bottom water quality, and sediment to explaining M-AMBI. The hours over the previous month DO was below 2 mg/L was the most important variable followed by the monthly maximum and mean value. Thus, bottom water quality measured via discrete CTD deployments at the time of sampling was not significant to explaining M-AMBI. Results support the application of M-AMBI to monitor impacts of hypoxia in temperate Gulf of Mexico estuaries. Our analysis further indicates that evaluating M-AMBI results in the context of eutrophication related stressors (i.e. low oxygen and hypoxia) may be significantly improved when paired with targeted high frequency monitoring of water quality conditions.