DEEPEND (Deep-Pelagic Nekton Dynamics) Consortium
The Deepwater Horizon Oil Spill (DWHOS) 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 deep-pelagic habitat is by far the largest affected by the DWHOS. Unfortunately the paucity of information about deep-ocean ecosystems in the Gulf of Mexico (GoM) limits our 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 ~1500 species of fishes that occur in the GoM, about half spend all or part of their lives in the open-ocean. Deep-pelagic fishes constitute the majority of fish biomass on Earth. Most mesopelagic (200-1000 m depth) species of fishes, as well as cephalopods and crustaceans, 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. Deep-pelagic nekton (fishes, shrimps and squids, collectively) also serve as prey for shallow-living game fishes, seabirds, and marine mammals. We must therefore develop the knowledge base required to estimate deep-pelagic vulnerability to impacts and recovery after disturbance, and we must develop means for valuation of deep-ocean ecosystem services.
The DEEPEND (Deep-Pelagic Nekton Dynamics of the Gulf of Mexico) Consortium has 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 GoM 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 2015-2020 (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.
The DEEPEND Consortium has conducted a 5-year sampling and analysis program that builds on the synergy developed during two intensive NOAA NRDA programs (ONSAP and DAP; 2010-2011), as well as added several new dimensions. In lieu of intervention for restoration in the classic sense, which is impractical in the deep pelagial, DEEPEND proposed expansion of knowledge as a restoration tool.
DEEPEND's four major research objectives were to:
1) Define community structure, abundance, and distribution of deep water column fauna;
2) Document biophysical drivers of ecosystem structure;
3) Determine genetic diversity among representative pelagic taxa;
4) Predict potential consequences of the DWHOS on the GoM pelagic fauna and microbial flora.