Trends and drivers of faunal abundance of the offshore Gulf of Mexico: Narrowing the data gap in the Gulf’s largest ecosystem component
The Deepwater Horizon oil spill (DWHOS) in the Gulf of Mexico was primarily a deep-pelagic (water column depths below 200 m) event. Variable amounts of discharged hydrocarbons and dispersant reached the ocean surface and/or seafloor, whereas 100% occurred within the water column, with a massive plume observed within the deep-pelagic realm (centered at ~1100 m). The Gulf’s deep-pelagic habitat, one of four ‘hyperdiverse’ deep-pelagic ecoregions on Earth, is by far the largest affected by the DWHOS and is the largest and least known habitat in the Gulf. Unfortunately, the paucity of information about deep-ocean ecosystems in the Gulf of Mexico has limited the ability to assess and predict the magnitude and consequences of changes to food webs and overall ecosystem structure. The likelihood of future spills, given the steady growth of oil exploration and operations, emphasizes the need to document acute and chronic effects on pelagic fauna.
Understanding the pelagic ecosystem is important. Of the ~1700 species of fishes that occur in the Gulf of Mexico, over half spend all or part of their lives in the open ocean. A significant portion of the Gulf’s offshore diversity comes from juvenile stages of coastal fauna, including managed reef fishes, suggesting that the inshore and offshore domains of the Gulf are highly connected. Deep-pelagic nekton (fishes, crustaceans, and cephalopods) comprise the majority of the water column fauna and are also the main prey of marine mammals and apex predators (i.e., tunas, billfishes, sharks, and seabirds) in the Gulf. Most mesopelagic (200-1000 m depth) nekton vertically migrate each night to feed in epipelagic (0-200 m) depths and return to deep water during the day. This behavior affects rapid cycling of natural and anthropogenic material in the water column (i.e., transporting carbon from surface to the deep ocean). We must therefore develop the knowledge base required to estimate deep-pelagic vulnerability to impacts and recovery after disturbance and develop means for valuation of deep-ocean ecosystem services.
From 2015-2020, the DEEPEND (Deep-Pelagic Nekton Dynamics of the Gulf of Mexico) Consortium, funded by the Gulf of Mexico Research Initiative, conducted a 5-year sampling and analysis program that built upon the synergy developed during two intensive NOAA NRDA programs (ONSAP and DAP; 2010-2015), as well as added several new dimensions. DEEPEND investigated deep-pelagic communities on short-term (sub-generational) and long-term (evolutionary) timescales to appraise extant recovery and potential future recovery of these communities, using a suite of integrated approaches. These approaches included: 1) a direct assessment of Gulf of Mexico deep-pelagic community structure, with simultaneous investigation of the physical and biological (including microbial) drivers of this structure, documenting biodiversity and ‘natural’ variability; 2) a time-series, ‘hindcast,’ comparison of biophysical data from 2015-2019 (DEEPEND sampling) to 2010-2011 DWHOS data; 3) an examination of differences in genetic diversity among key species; and 4) an assessment of the extant and potential future consequences of the DWHOS on the shallow and deep-pelagic biota. Publications and datasets produced from this work are listed under the Products tab.
DEEPEND is now supported by the NOAA RESTORE Science Program (DEEPEND|RESTORE) to expand upon this decade-long, open-ocean research in the Gulf of Mexico and investigate the long-term trends in fishes, crustaceans, and cephalopods in the deep-pelagic Gulf. DEEPEND|RESTORE will produce assessments of pelagic faunal abundance since the spill to support ecosystem-based management and restoration in the open-ocean Gulf of Mexico.
DEEPEND|RESTORE’s major research objectives are to:
1) Conduct quantitative analyses of the oceanic Gulf fauna over time and space;
2) Identify sentinel species whose abundances reflect ecosystem state in the Gulf, and possible responses to disturbance
3) Classify pelagic habitat structure and biophysical drivers of community structure;
4) Produce identification guides for the oceanic Gulf fauna
5) Develop analytical indicators (e.g., biochemical markers) of oceanic ecosystem state
6) Integrate this information with ongoing resource management in the Gulf of Mexico.