Students Jessica Diller (bottom) and Kamala Earl (top) prepare enclosed treatment plots in oiled marshes of Barataria Bay, La. (Photo by Gabriel

Studies Explore the Dynamics of How Offshore Oil Spills Affect Coastal Environments

Oil from the 2010 Deepwater Horizon incident moved from deep waters to coastal shorelines, overwhelming their natural defenses which, in turn, slowed or prevented their recovery. Scientists with the Gulf of Mexico Research Initiative (GoMRI) have been assessing the health of these complex environments that experience stressors from multiple sources, providing information that can inform response decisions during future disturbances.

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Conceptual representation of transport of sinking particles. In Spring 2012 (a) particles collected at traps originated from confined, common areas to the north of the traps far from large mesoscale features. In Fall 2012 (b) a large Loop Current eddy dominated the circulation, and particles collected at GC600 originated from the eddy periphery and from inshore, river-influenced high-productive waters. For more details, see Figure 7 in the publication (used with permission from Guangpeng Liu).

Study Simulates How Large and Small Circulations Influence Sinking Marine Particles

Scientists used 3D regional ocean model simulations and sediment trap data to investigate how large (mesoscale) and small (submesoscale) circulations affect the transport of sinking particles, or marine snow, in the northern Gulf of Mexico. Small-scale convergence and divergence processes (a few kilometers) and cross-shore transport of riverine inputs induced by mesoscale eddies significantly influenced the speed and trajectory of sinking particles in offshore waters.

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Dolphin. Provided by Kaitlin Frasier.

Study Uses Big-Data Approach to Identify Distinct Dolphin “Clicks” in Acoustic Recordings

Researchers designed an automated network-based classification method to process large acoustic datasets and identify distinct dolphin click types without requiring prior knowledge of their distinguishing features. The method identified seven click types from over 50 million echolocation clicks recorded in the Gulf of Mexico – six clicks of unknown origin and one click belonging to the Risso’s dolphin species.

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Researchers used CTD and Niskin bottle rosettes to collect dissolved organic carbon samples aboard the R/V Pelican. In the distance is a nearby drilling ship on the Gulf of Mexico. Photo credit: Brad Rosenheim

Study Characterizes Dissolved Organic Carbon Cycling in the Northern Gulf of Mexico

Researchers analyzed dissolved organic carbon from water column samples collected in five regions to establish baseline data about its relative persistence and cycling in the northern Gulf of Mexico. The team found that the Mississippi River exports large amounts of dissolved organic carbon with an anthropogenic 14C signature, which is removed and recycled offshore as the river plume moves offshore.

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Study author Uta Passow prepares treatments for roller table experiments. Image provided by Passow.

Study Explores Complex Dispersant Effects on Marine Oil Snow Formation

Researchers simulated the sinking of marine particle aggregates in oil-dispersant mixtures to assess how Corexit chemical dispersant affects specific biological processes involving marine oil snow formation. The team found that Corexit could significantly enhance or inhibit marine oil snow formation depending on application timing and location and interactions with other water column compounds, making its influence difficult to predict.

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This study (Nature Ecology & Evolution, Johansen et al., 2017) used larval fishes like this. Image by Jacob Johansen.

Study Finds Low Oil Concentrations Impair Self-Preservation Behaviors in Coral Reef Fish Larvae

Researchers from the United States, Australia, and Europe conducted mesocosm experiments to assess how larval reef fishes respond physiologically and cognitively to low crude oil concentrations. The team observed that polycyclic aromatic hydrocarbons (PAHs), at levels recorded in industrialized sections of tropical coral reefs worldwide, increased larvae mortality and stunted growth rates.

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Sheepshead minnow. Photo credit: C. Filosa

Study Finds Different Avoidance Behaviors in Estuarine Fish to Oiled Sediment

A Louisiana State University researcher conducted laboratory experiments to learn how estuarine fish behave around sediments containing varying concentrations of weathered and fresh oil. He observed that fish exhibited a stronger avoidance response to medium and high concentrations of fresh oil compared to low concentrations and observed no significant avoidance of any weathered oil concentrations.

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An epifluorescence microphotograph of a complex bacterial community feasting on or associated with an oil floc (pink). Gammaproteobacteria (green) are the majority of cultured, well-studied alkane- and aromatics-degrading bacteria. Other bacteria (blue) thrive in close association with the oil particle and their gammaproteobacterial neighbors. (Photo by Luke McKay, Montana State University).

Study Analyzes Metabolic Pathways of Oil-Degrading Bacteria

Researchers analyzed bacterial communities exposed to Deepwater Horizon oil and identified taxa and genes associated with oil degradation and assimilation. The scientists found that Marinobacter and Alcanivorax dominated alkane-degrading communities, while Alteromonadales, Oceanospirillales, and Rhodospirillales dominated polycyclic aromatic hydrocarbon (PAH)-degrading communities.

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Study Finds UV Exposure Late in Mahi-Mahi Embryo Development Enhances Oil Toxicity

Researchers conducted laboratory experiments on mahi-mahi embryos to determine the effects of ultraviolet radiation (UV) and oil co-exposure during different times in their development. The team observed that UV affected the success of mahi-mahi hatch in all exposure scenarios compared to controls but was highest (a 1.6- to 6-fold increase) when co-exposure occurred late in embryonic development.

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Study Investigates Influence of Hurricanes on Ocean Surface Currents

Scientists used GPS data collected from ocean drifters during Hurricane Isaac with a coupled atmosphere-wave-ocean model to better understand how hurricanes affect upper ocean circulation. The researchers found that hurricane-induced Stokes drift (wind-wave-driven water mass transport) created a cyclonic rotational flow to the storm’s left and an anticyclonic rotational flow to its right.

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Study Examines Transformation of Weathered Oil in Saltmarsh Sediment

Scientists analyzed weathered and fresh Macondo oil to learn about oil products resulting from microbial degradation and photochemical reactions. They observed that 48 months after the Deepwater Horizon spill, less than 1 percent of oil remained in marsh sediments collected from heavily-impacted sites; however, it was still 400 times greater than sites with moderate-to-no observed oiling.

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A Cuviers’ beaked whale. (Photo courtesy of Ocean Treasures Memorial Library)

Study Estimates Beaked Whale Populations in Gulf of Mexico

Scientists used passive acoustic monitoring during 2010-2013 to detect the presence of beaked whales in the Gulf of Mexico. These animals are difficult to study visually because they spend little time at the sea surface and are only present in offshore deep waters; they are rarely found on the continental shelf and near-shore waters.

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