The largest accidental marine oil spill (4.9 million
barrels) in the Gulf of Mexico (GoM) seabed (1600 m) caused by the sinking of
the Deepwater Horizon oil rig in 2010, put to the test once again the resilient
capacity of the pelagic and benthic realms of this Large Marine Ecosystem. Many
are the ecological services provided by its waters (fisheries, tourism,
aquaculture and fossil fuel reserves) to neighboring countries (US, Mexico and
Cuba). However, the unprecedented volumes of hydrocarbons, gas and chemical
dispersants (Corexit) introduced in the system, represent ecological stressors
whose deleterious effects are still the subject of civil claims and scientific
controversy. Presumably, the short scale effects were confined to the Gulf’s
northeastern shallow waters, and the combined actions of weathering, biodegradation,
and oil recovery left the system almost under pre-spill conditions.
Unfortunately, surface and subsurface oil plumes were detected in the spill
aftermath, and their dispersion trajectories threatened Mexico EEZ. Surface oil
slicks were detected in the pristine waters of northern Yucatán, while
subsurface oil plumes from the Macondo’s well blowout were dangerously
advancing southwest towards key fishing grounds in the northwestern GoM. This
disaster prompted the Mexican government to implement an ambitious ocean
monitoring program adopting a bottom-up approach focused on building a base
line for more than 42 physicochemical and biological variables for water,
sediment and biota from the continental shelf-slope region of the NW GoM. Technological
constraints have precluded systematic observations in the vast Mexican EEZ that
could discriminate natural variability and oil seep emissions from antropic
disturbances. Therefore, preliminary risk analyses relied on seasonal and historical
records. Two years of field observations revealed subtle environmental changes
in the studied area attributed to antropic disturbances. Waters maintained
oligotrophic conditions and zooplankton and benthic infaunal biomass were also
poor. Biomarkers in sediments and biota did not exceed EPA’s benchmarks, and
sediment’s fingerprinting (δ13C) indicated marine carbon sources.
Geomarkers revealed an active transport from the Mississippi towards the NW GoM
of phyllosilicates bearing a weathered oil coating. Consequently, shelf and
slope sediment toxicity begins to show an increasing trend in the region. The
complexity of hydrocarbons bioaccumulation and biodegradation processes in deep
waters of the GoM seems to indicate that meso-and large-scale observations may
prove to be essential in understanding the capacity of the GoM to recover its
ecological stability.