A tale of two Gulf spills: A research consortium of 19 institutions from 5 countries studying the impacts of oil spills on the Gulf of Mexico.
This article published in ICES Journal of Marine Science explains new methods used to validate the age of Red Snapper otoliths with regional corals in the Gulf of Mexico.
Radiocarbon (Δ14C) was analyzed in northern Gulf of Mexico (nGOM) red snapper (Lutjanus campechanus) otolith cores (n = 23), otolith edge samples (n = 12), and whole age-0 otoliths (n = 9), with edge samples and whole age-0 otoliths constituting known-age samples. There was no significant difference in the linear relationship of Δ14C versus year of formation between regional corals and known-age otolith samples, and a linear regression fit to the combined data from 1980 to 2015 extends the utility of the bomb radiocarbon chronometer for age validation. The entire regional coral and known-age otolith data set (1940 to 2015) was then utilized as a reference series to validate otolith-derived red snapper age estimates for cored otolith samples. A loess regression was fit to the reference data and then the sum of squared residuals (SSR) was computed from predicted versus observed birth years for cored adult otolith samples. This process was then repeated for ages biased ±1–4 years. Ages with no bias applied had the lowest SSR, thus validating red snapper age estimates and demonstrating the utility of the combined regional coral and known-age red snapper otolith Δ14C time series for age validation of nGOM marine fishes.
How much Sargassum was in contact with oil from the 2010 Deepwater Horizon spill? Using Landsat and AVIRIS satellite imagery and 2010-2011 NRDA observations, the authors estimated Sargassum coverage in oiled areas ranged from 1296 ± 453 km2 (for areas with > 5% thick oil) to 736 ± 257 km2 (for areas with > 10% thick oil).
The most significant result from this study is the finding that all satellite instruments and high-altitude airborne instruments will miss significant amounts of Sargassum in all seasons. Therefore, even though they could provide general distributions of large Sargassum patches, satellite data alone are insufficient to provide accurate estimates of the total Sargassum coverage. Scaling factors using the much higher-resolution observations from low-altitude airborne measurements are required to provide a more accurate estimate of Sargassum coverage. At present, the Landsat-based Sargassum coverage estimates scaled using low-altitude airborne measurements represent our best knowledge of Sargassum coverage before, during, and after the DWH oil spill in 2010.
Full Citation: Hu, C.; Hardy, R.; Ruder, E.; Geggel, A.; Feng, L.; Powers, S.; Hernandez, F.; Graettinger, G.; Bodnar, J.; McDonald, T. (2016) Sargassum coverage in the northeastern Gulf of Mexico during 2010 from Landsat and airborne observations: Implications for the Deepwater Horizon oil spill impact assessment, Marine Pollution Bulletin, Volume 107, Issue 1, 15 June 2016, Pages 15-21, http://dx.doi.org/10.1016/j.marpolbul.2016.04.045.
This article develops a marine food web matrix for the Gulf of Mexico (GOM) based on local stomach sampling and online diet information. Working at the level of functional groups, we fit diet information to a statistical model based on the Dirichlet distribution. This allows us to quantify likely contributions of prey to predators’ diets. Error ranges on these values reflect diet variability and data quality, and help in identifying functional groups that would benefit from additional sampling. We perform hierarchical cluster analysis to determine functional groups that have similar prey requirements, then produce a food web diagram representing the interactions between predators and prey. A meta-analysis using principle coordinate analysis allows us to compare this study’s diet matrix with ten other published GOM food webs and determine where variation in food web structure exists. We also compare our new food web to the diet matrix used by the Ainsworth et al. (2015) Atlantis ecosystem model, a strategic tool developed to assess ecosystem dynamics in the GOM. A hindcast from 1980 to 2010 using Atlantis shows an improved fit to observational data and reduced error in biomass projections using the revised diet information.
Source: Joseph H. Tarnecki, Amy A. Wallace, James D. Simons, Cameron H. Ainsworth, Progression of a Gulf of Mexico food web supporting Atlantis ecosystem model development, Fisheries Research, Volume 179, July 2016, Pages 237-250, ISSN 0165-7836, http://dx.doi.org/10.1016/j.fishres.2016.02.023.
The Deepwater Horizon oil spill was the largest in US history, unprecedented for the depth and volume of oil released, the amount of dispersants applied, and the unexpected, protracted sedimentation of oil-associated marine snow (MOS) to the seafloor. Marine snow formation, incorporation of oil, and subsequent gravitational settling to the seafloor (i.e., MOSSFA: Marine Oil Snow Sedimentation and Flocculent Accumulation) was a significant pathway for the distribution and fate of oil, accounting for as much as 14% of the total oil released. Long residence times of oil on the seafloor will result in prolonged exposure by benthic organisms and economically important fish. Bioaccumulation of hydrocarbons into the food web also has been documented. Major surface processes governing the MOSSFA event included an elevated and extended Mississippi River discharge, which enhanced phytoplankton production and suspended particle concentrations, zooplankton grazing, and enhanced microbial mucus formation. Previous reports indicated that MOS sedimentation also occurred during the Tsesis and Ixtoc-I oil spills; thus, MOSSFA events may occur during future oil spills, particularly since 85% of global deep-water oil exploration sites are adjacent to deltaic systems. We provide a conceptual framework of MOSSFA processes and identify data gaps to help guide current research and to improve our ability to predict MOSSFA events under different environmental conditions. Baseline time-series data and model development are urgently needed for all levels of ecosystems in regions of hydrocarbon extraction to prepare for and respond to future oil spills and to understand the impacts of oil spills on the environment.
Ref: Daly, K. L., Passow, U., Chanton, J., Hollander, D. Assessing the impacts of oil-associated marine snow formation and sedimentation during and after the Deepwater Horizon oil spill, Antropocene, 2016.
When wind speeds are 2–10 m s−1, reflective contrasts in the ocean surface make oil slicks visible to synthetic aperture radar (SAR) under all sky conditions. Neural network analysis of satellite SAR images quantified the magnitude and distribution of surface oil in the Gulf of Mexico from persistent, natural seeps and from the Deepwater Horizon (DWH) discharge. This analysis identified 914 natural oil seep zones across the entire Gulf of Mexico in pre-2010 data. Their ∼0.1 µm slicks covered an aggregated average of 775 km2. Assuming an average volume of 77.5 m3 over an 8–24 h lifespan per oil slick, the floating oil indicates a surface flux of 2.5–9.4 × 104 m3 yr−1. Oil from natural slicks was regionally concentrated: 68%, 25%, 7%, and <1% of the total was observed in the NW, SW, NE, and SE Gulf, respectively. This reflects differences in basin history and hydrocarbon generation. SAR images from 2010 showed that the 87 day DWH discharge produced a surface-oil footprint fundamentally different from background seepage, with an average ocean area of 11,200 km2 (SD 5028) and a volume of 22,600 m3 (SD 5411). Peak magnitudes of oil were detected during equivalent, ∼14 day intervals around 23 May and 18 June, when wind speeds remained
Natural oil slicks in the western Gulf of Mexico are used to determine the sun glint threshold required for optical remote sensing of oil films. The threshold is determined using the same-day image pairs collected by Moderate Resolution Imaging Spectroradiometer (MODIS) Terra (MODIST), MODIS Aqua (MODISA), and Visible Infrared Imaging Radiometer Suite (VIIRS) (N = 2297 images) over the same oil slick locations where at least one of the sensors captures the oil slicks. For each sensor, statistics of sun glint strengths, represented by the normalized glint reflectance (LGN, sr−1), when oil slicks can and cannot be observed are generated. The LGN threshold for oil film detections is determined to be 10−5–10−6 sr−1 for MODIST and MODISA, and 10−6–10−7 sr−1 for VIIRS. Below these thresholds, no oil films can be detected, while above these thresholds, oil films can always be detected except near the critical-angle zone where oil slicks reverse their contrast against the background water.
It has long been observed that oil slicks under sunglint can reverse their optical contrast against nearby oil-free seawater. Such a phenomenon has been described through both empirical statistical analysis of the sunglint strength and modeled theoretically using a critical angle concept. The critical angle, in this model, is the angle at which the image pixels show no or negligible contrast between oiled and nonoiled seawater. Pixels away from this critical angle show either positive or negative contrast from the oil-free pixels. Although this concept has been fully demonstrated in the published literature, its calculation needs to be further refined to take into account: (1) the different refractive indices of oil slicks (from natural seeps) and seawater and (2) atmospheric effects in the sensor-measured radiance. Using measurements from the Moderate Resolution Imaging Spectroradiometer (MODIS) over oil films in the Gulf of Mexico, we show improvement in the modeled and MODIS-derived reflectance over oil slicks originated from natural seeps after incorporating these two factors in the model. Specifically, agreement between modeled and measured sunglint reflectance is found for both negative and positive-contrasting oil slicks. These results indicate that surface roughness and reflectance from oil films can be estimated given any solar/viewing geometry and surface wind. Further, this model might be used to correct the sunglint effect on thick oil under similar illumination conditions. Once proven possible, it may allow existing laboratory-based models, which estimate oil thickness after such corrections, to be applied to remote sensing imagery.
Ref: Lu, Y., S. Sun, M. Zhang, B. Murch, and C. Hu (2015), Refinement of the critical angle calculation for the contrast reversal of oil slicks under sunglint, J. Geophys. Res. Oceans, 120, doi:10.1002/2015JC011001
Using fine spatial resolution (~ 7.6 m) hyperspectral AVIRIS data collected over the Deepwater Horizon oil spill in the Gulf of Mexico, we statistically estimated slick lengths, widths and length/width ratios to characterize oil slick morphology for different thickness classes. For all AVIRIS-detected oil slicks (N = 52,100 continuous features) binned into four thickness classes (≤ 50 μm but thicker than sheen, 50–200 μm, 200–1000 μm, and > 1000 μm), the median lengths, widths, and length/width ratios of these classes ranged between 22 and 38 m, 7–11 m, and 2.5–3.3, respectively. The AVIRIS data were further aggregated to 30-m (Landsat resolution) and 300-m (MERIS resolution) spatial bins to determine the fractional oil coverage in each bin. Overall, if 50% fractional pixel coverage were to be required to detect oil with thickness greater than sheen for most oil containing pixels, a 30-m resolution sensor would be needed.
Ref: Sun, S., C. Hu, L. Feng, G. A. Swayze, J. Holmes, G. Graettinger, I. MacDonald, O. Garcia and I. Leifer (2015). Oil slick morphology derived from AVIRIS measurements of the Deepwater Horizon oil spill: Implications for spatial resolution requirements of remote sensors. Marine Pollution Bulletin, in press, doi:10.1016/j.marpolbul.2015.12.003
The Ixtoc-I oil spill occurred in 1979 in shallow waters (50 m) of the Bay of Campeche, Mexico. Although it is known that a large portion of the released oil from this second largest accidental marine oil spill in history reached the surface, to date there has been no attempt to document the surface footprint and trajectory of the released oil. Our study attempts to fill this knowledge gap using remote sensing data collected by Landsat/MSS and CZCS. Both showed the same general patterns of oil trajectory to the northwest and north, nearly parallel to the coastline of the western Gulf of Mexico (GoM) with possible oil landing on Mexican and Texas beaches. Field observations at selected beaches and islands along the coast of the western and southern GoM during and after the spill confirmed these satellite-based findings, which were also used to help in planning a recent field campaign to collect sediment samples in the southern GoM.
A phytoplankton bloom covering an area > 11,000 km2 has been reported in the northeastern Gulf of Mexico east of the Mississippi River Delta in August 2010 (30°–28° N, 90°–86° W) based on NASA Moderate Resolution Imaging Spectrometer (MODIS) chlorophyll fluorescence line height (FLH) images. The bloom appeared to be anomalous relative to a historical monthly chlorophyll FLH mean (August 2002 to 2010), and was attributed by others to the Deepwater Horizon (DWH) oil spill accident. Here we tested an alternative hypothesis that the eastward dispersal of the Mississippi River plume entrained in wind-driven currents contributed to the development of this phytoplankton bloom. We examined Mississippi River discharge and nutrient records, ship-based surface salinity data, and the time-series of MODIS ocean color and FLH images. Wind measurements from buoys showed winds > 6 m s− 1 first in a southerly (northward) direction August 8–10, and then in a northerly (southward) direction until August 26. Results from the American Seas-Navy Coastal Ocean Model (AmSeas-NCOM) show how coastal water was advected in wind-driven currents into the area of the northeastern Gulf of Mexico where the bloom was documented. Between July 9 and September 8, 2010, the discharge of the Mississippi River exceeded the 20-year mean. During this time, the northeastern Gulf received an estimated excess volume of approximately 8.3 × 109 m3 relative to the 20-year mean. Together with findings from a particle trajectory model, we conclude that nutrients and other materials (e.g., sediments) from the excessive discharge of the Mississippi River and adjacent marshes and wind-driven currents likely contributed to the anomalous bloom observed during August 2010 and to the anomalously high organic matter sedimentation rates observed in the northeastern Gulf of Mexico in the aftermath of the Deepwater Horizon oil spill.
Remote detection of pelagic Sargassum is often hindered by its spectral similarity to other floating materials and by the inadequate spatial resolution. Using measurements from multi-spectral satellite sensors (Moderate Resolution Imaging Spectroradiometer or MODIS), Landsat, WorldView-2 (or WV-2) as well as hyperspectral sensors (Hyperspectral Imager for the Coastal Ocean or HICO, Airborne Visible-InfraRed Imaging Spectrometer or AVIRIS) and airborne digital photos, we analyze and compare their ability (in terms of spectral and spatial resolutions) to detect Sargassum and to differentiate it from other floating materials such as Trichodesmium, Syringodium, Ulva, garbage, and emulsified oil. Field measurements suggest that Sargassum has a distinctive reflectance curvature of ~ 630 nm due to its chlorophyll c pigments, which provides a unique spectral signature when combined with the reflectance ratio between brown (~ 650 nm) and green (~ 555 nm) wavelengths. For a 10-nm resolution sensor on the hyperspectral HyspIRI mission currently being planned by NASA, a stepwise rule to examine several indexes established from 6 bands (centered at 555, 605, 625, 645, 685, 755 nm) is shown to be effective to unambiguously differentiate Sargassum from all other floating materials Numerical simulations using spectral endmembers and noise in the satellite-derived reflectance suggest that spectral discrimination is degraded when a pixel is mixed between Sargassum and water. A minimum of 20–30% Sargassum coverage within a pixel is required to retain such ability, while the partial coverage can be as low as 1–2% when detecting floating materials without spectral discrimination. With its expected signal-to-noise ratios (SNRs ~ 200:1), the hyperspectral HyspIRI mission may provide a compromise between spatial resolution and spatial coverage to improve our capacity to detect, discriminate, and quantify Sargassum.
Ref:Chuanmin Hu, Lian Feng, Robert F. Hardy, Eric J. Hochberg, Spectral and spatial requirements of remote measurements of pelagic Sargassum macroalgae, Remote Sensing of Environment, Volume 167, 15 September 2015, Pages 229-246, ISSN 0034-4257, http://dx.doi.org/10.1016/j.rse.2015.05.022.
Satellite images of reflected sunlight have been used to detect and monitor oil spills in oceans. However, such a capacity is often hindered by the image noise due to either a low signal-to-noise ratio or other image features such as clouds or cloud shadows. The problem is particularly severe for nighttime images captured by the Visible Infrared Imager Radiometer Suite (VIIRS). This letter proposes a practical method to extract oil slick features in a semiautomatic fashion from VIIRS nighttime images and other noisy optical remote sensing images. The method is based on statistical information and morphological operators, and it is demonstrated to be able to effectively remove the noise and identify line features with the appropriate selection of threshold values. Testing this method over VIIRS nighttime images shows the preliminary success of oil slick feature extraction. Experiments on daytime data collected by the Moderate Resolution Imaging Spectroradiometer (MODIS) also suggest the applicability of this method to other optical remote sensing images. However, the requirement of human intervention to determine optimal parameters points to the need for improved automation in future works.
Ref: Wang, M. and C. Hu "Extracting Oil Slick Features From VIIRS Nighttime Imagery Using a Gaussian Filter and Morphological Constraints," in Geoscience and Remote Sensing Letters, IEEE , vol.12, no.10, pp.2051-2055, Oct. 2015 doi: 10.1109/LGRS.2015.2444871.)
Beaked whales are deep diving elusive animals, difficult to census with conventional visual surveys. Methods are presented for the density estimation of beaked whales, using passive acoustic monitoring data collected at sites in the Gulf of Mexico (GOM) from the period during and following the Deepwater Horizon oil spill (2010–2013). Beaked whale species detected include: Gervais’ (Mesoplodon europaeus), Cuvier’s (Ziphius cavirostris), Blainville’s (Mesoplodon densirostris) and an unknown species of Mesoplodon sp. (designated as Beaked Whale Gulf — BWG). For Gervais’ and Cuvier’s beaked whales, we estimated weekly animal density using two methods, one based on the number of echolocation clicks, and another based on the detection of animal groups during 5 min time-bins. Density estimates derived from these two methods were in good general agreement. At two sites in the western GOM, Gervais’ beaked whales were present throughout the monitoring period, but Cuvier’s beaked whales were present only seasonally, with periods of low density during the summer and higher density in the winter. At an eastern GOM site, both Gervais’ and Cuvier’s beaked whales had a high density throughout the monitoring period.
Ref:J. Hildebrand, S. Baumann-Pickering, K. Frasier, J. Trickey, K. Merkens, S. Wiggins, M. McDonald, L. Garrison, D. Harris, T. Marques, and L. Thomas: Passive acoustic monitoring of beaked whale densities in the Gulf of Mexico, Scientific Reports, 5, 16343, doi: 10.1038/srep16343 (2015)
Red Snapper Lutjanus campechanus were sampled at 33 natural and 27 artificial reef sites in the northern Gulf of Mexico prior to (2009–2010) and after (2010–2011) to examine potential diet and trophic shifts following the Deepwater Horizon (DWH) oil spill. We dissected 708 stomachs for gut content analysis and processed 65 muscle tissue samples for stable isotope ratio-mass spectrometry analysis of δ13C, δ15N, and δ34S. Forty-eight percent of stomachs contained identifiable prey, which we grouped into seven categories: fish, decapods, cephalopods, stomatopods, gastropods, zooplankton, and other invertebrates. Based on these categories, Red Snapper diet was significantly different following the DWH oil spill, and was differentially affected by fish size. The interaction between habitat (natural versus artificial reefs) and DWH oil spill effects was also significant. Significant differences in diet among Red Snapper size-classes were due to low trophic position prey, such as pelagic zooplankton, being more abundant in the diet of larger (>500 mm) Red Snapper, while decapods and fish constituted a higher proportion of the diet of smaller individuals. Red Snapper consumed higher amounts of decapods at artificial (21.9% by mass) versus natural (14.8%) reef sites, but the habitat effect on diet was not significant. The habitat × DWH timing interaction was driven by a decrease in zooplankton consumed at both habitat types, increased benthic prey at natural reefs, and increased fish consumption at artificial reefs in post-DWH oil spill samples. Stable isotope data indicated a postspill increase in Red Snapper trophic position (15N enrichment) and an increase in benthic versus pelagic prey (34S depletion), both consistent with observed dietary shifts. Overall, results indicate shifts in Red Snapper diet and trophic position occurred following the DWH oil spill, thus the relative abundance of prey resources likely changed.
The full article is available at the link below:
Tarnecki, J. H., & Patterson III, W. F. (2015). Changes in Red Snapper Diet and Trophic Ecology Following the Deepwater Horizon Oil Spill. Marine and Coastal Fisheries, 7(1), 135–147.
Following the 2010 Deepwater Horizon (DWH) blowout, we surveyed offshore demersal fishes in the northern Gulf of Mexico (GoM) in 2011-2013, to assess polycyclic aromatic hydrocarbon (PAH) exposure. Biliary PAH metabolites were estimated in 271 samples of golden tilefish (Lopholatilus chamaeleonticeps), king snake eel (Ophichthus rex) and red snapper (Lutjanus campechanus), using high performance liquid chromatography with fluorescence detection. Mean concentration of naphthalene (NPH) metabolites in golden tilefish (240µg g-1) was significantly higher (p=0.001) than in red snapper (61µg g-1) or king snake eel (38µg g-1). Biliary NPH metabolite concentration decreased over the study period in red snapper (58%) and king snake eel (37%), indicating likely episodic exposure, while concentrations were persistently high in golden tilefish. Naphthalene metabolite levels measured in golden tilefish are among the highest concentrations measured in fishes globally, while concentrations for red snapper and king snake eel are similar to pre-DWH levels measured in GoM species. In contrast, concentrations of benzo[a]pyrene metabolites were similar for all three species (p=0.265, mean 220ng g-1) and relatively low when compared to GoM, global data and previous oil spills. These data support previous findings that fish life history and physiology play significant roles in exposure and uptake of PAH pollution.
On 20 April 2010, the Deepwater Horizon drilling rig lost well control while drilling at the Macondo prospect in the Gulf of Mexico. At the time of the Macondo blowout, the academic scientific community was ill prepared to initiate and rapidly conduct the necessary coordinated interdisciplinary studies of the environments around the discharge area.
Ref: Joye, S., J. Montoya, S. Murawski, T. Özgökmen, T. Wade, R. Montuoro, B Roberts, D. Hollander, W. H. Jeffrey, J. Chanton, and C. Wilson. Fast Action: A Collaborative, Multi-Disciplinary Rapid Response Study of the Hercules Gas Well Blowout, AGU EOS, 2014.
Using data collected over the Gulf of Mexico during night between May 2012 and September 2013 by the Visible Infrared Imager Radiometer Suite (VIIRS), we demonstrate a new application from its day-and-night band (DNB). Under cloud free and moon glint conditions, the DNB revealed surface oil slicks from natural oil seeps. This is despite the fact that the signal-to-noise ratio (SNR) of this wide band (505–890 nm) under moon glint is much lower (30:1–50:1) and its resolution is also coarser (750 m) than the VIIRS imaging bands (375 m) under daytime solar illumination. The DNB was designed to map light sources at night. Similar to its predecessor, the Defense Meteorological Satellite Program Operational Linescan System (OLS), the VIIRS DNB should be suitable to identifying bioluminescence at night. However, with its finer resolution and higher SNR than OLS, the VIIRS DNB is demonstrated here to be also able to complement other sensors in the detection and mapping of oil spills.
Ref: Hu, C., Chen, S., Wang, M., Murch, B., Taylor, J. Detecting surface oil slicks using VIIRS nighttime imagery under moon glint: A case study in the Gulf of Mexico, Remote Sensing Letters, 2015, 6(4), 295-301.
A recent study from the University of Delaware published in Aquatic Biology explored the effects of oil-spill related chemicals on the ctenophore Mnemiopsis leidyi. M. leidyi is an important species in the pelagic ecosystem, acting as both predator and prey for many other species. It has been suggested that they may serve as vectors of hydrocarbons in pelagic food webs. Polycyclic aromatic hydrocarbons (PAHs) accumulate in their tissues following oil exposure. PAHs then accumulate in the tissues of their predators, and so on.
M. leidyi reactions to oil, dispersed oil, and chemical dispersant were studied at different temperatures. These temperatures reflect ocean temperatures during different seasons, providing information about effects of spills occurring at different times of the year. The sublethal effects studied were respiration rate, bioluminescence, and glutathione-s-transferase (GST) activity. Respiration rate can serve as a proxy for metabolic rate. Bioluminescence is usually used as a predator deterrent. Increased GST activity indicates upregulation of cellular detoxification pathways.
Mortality of M. leidyi was found to be concentration dependent at both temperatures for all three chemicals. Higher mortality occurred at higher temperatures and concentrations. However, oil concentrations in the Gulf of Mexico following the Deepwater Horizon spill were well below lethal levels for M. leidyi at both temperatures. Similarly, concentrations of dispersant used in this study were higher than what would be found in the ocean during mitigation for an oil spill. The dispersant was more toxic than the crude oil, and apparently increased the toxicity of the oil when mixed. PAH concentrations in tissues were largest when exposed to chemical dispersant and smallest when exposed to oil with no dispersant.
There was no significant difference in respiration rate when exposed to any of the chemicals. This indicates that there was no increase in aerobic metabolic demand due to upregulation of detoxification pathways or locomotive attempts to avoid oil. However, the author suggests that this topic be studied in more depth to determine if changes in respiration rates occur over a shorter or longer time period than the one studied. The oil and dispersed oil had no significant effect on GST activity, but increased dispersant concentrations did result in high GST activity. The total amount of bioluminescent light emitted decreased as concentrations of all three chemicals increased. This was dependent on temperature, as bioluminescence is temperature dependent in normal conditions. The cause for these increases is unknown. It is also unknown how bioluminescence would be affected outside the lab, in natural predator-prey interactions.
For more information and to read the full article, visit the University of Delaware's Library webpage.
Habitat-specific density and diet of rapidly expanding invasive red lionfish, Pterois volitans, populations in the Northern Gulf of Mexico
Invasive lionfish were first reported in the Gulf of Mexico in the summer of 2010. Their density and size distributions were examined from the fall of 2010 to 2013 to examine their potential impacts on native fish communities. During the sampling period, lionfish populations increased exponentially. Lionfish density at artificial reef locations was two orders of magnitude higher than at natural reef sites. Their diet varied among habitats, seasons, and size classes. Results indicate that lionfish are mesopredators in the northern Gulf becoming more piscivorous at larger sizes. Their diet was more varied at the artificial reef sites where they were foraging on open substrates away from the reef structures. The study has implications for tracking lionfish invasions in the nGoM as well as estimating their impacts on native reef fish communities.
Ref: Dahl, K. A., Patterson, W. F. III. Habitat-specific density and diet of rapidly expanding invasive red lionfish, Pterois volitans, populations in the Northern Gulf of Mexico, PLoS One 9(8):e105852.
Enhancing the ocean observing system to meet restoration challenges in the Gulf of Mexico
As a result of fines and penalties generated by the settlement of civil and criminal actions and the Natural Resource Damage Assessment and Restoration (NRDAR) claims resulting from the Deepwater Horizon (DWH) incident, various entities are poised to receive billions of dollars to improve the health and resilience of the Gulf of Mexico large marine ecosystem. While much of the funding will go to economic development in states impacted by the oil spill, the lion’s share will be used to restore specific natural resources damaged as a result of DWH and to tackle larger and more chronic environmental issues such as loss of wetlands, nutrient enrichment, fisheries sustainability, and toxic contaminant management. In addition, the federal RESTORE Act directs that some of these funds will be used to improve long-term monitoring of the Gulf of Mexico ecosystem.
It was clear during the DWH response phase that important ocean parameters, such as current speed and direction, water chemistry, air quality, and biological effects of oil exposure, were not being sampled well, necessitating significant technology upgrades (Lubchenco et al., 2012). Many of these observations have not been sustained. Before making new observing investments, however, the objectives, priorities, and governance across the many entities involved (Table 1) need to be critically considered. The outcome of these deliberations should be a coastal and ocean observing system that is right-sized, with a unified set of priorities, that is capable of supplying adequate science to restoration planners, and that realizes the specific intents of these new funds in ways that are both cost-effective and forward-looking.
The President charged the Gulf Coast Ecosystem Restoration Task Force (2011) to develop a Gulf of Mexico Regional Ecosystem Restoration Strategy, and in doing so stipulated four overarching goals: (1) restore and conserve habitat, (2) restore water quality, (3) replenish and protect coastal and marine living resources, and (4) enhance community resilience. These goals are specific and outcome-oriented and therefore should guide the development of priorities for enhancing the science supporting them. The Task Force has since been replaced by the Gulf Coast Ecosystem Restoration Council, which has adopted the four Task Force goals and added a fifth: restore and revitalize the economy (Gulf Coast Ecosystem Restoration Council, 2013.
Prevalence of External Skin lesions and Polycyclic Aromatic Hydrocarbon Concentrations in the Gulf of Mexico Fishes, Post-Deepwater Horizon
Abstract: We surveyed offshore fish populations in the Gulf of Mexico in 2011 and 2012, following persistent reports of abnormal skin lesions and other pathologies in the aftermath of the Deepwater Horizon oil spill. The incidence of skin lesions in 2011 sampling was most frequent in some bottom-dwelling species along the continental shelf edge north of the Deepwater Horizon site. Longline surveys revealed that by 2012 the overall frequency of lesions in northern Gulf of Mexico (NGM) fishes in the vicinity of the Deepwater Horizon had declined 53%, with severity also declining. Relatively high concentrations of polycyclic aromatic hydrocarbon (PAH) metabolites (up to 470,000 ng naphthalene equivalents/g bile wet weight), indicative of oil-related pollution, were found in fish bile in 2011; concentrations of summed PAHs measured in fish liver and muscle were relatively low (<35 ng/g) due to the efficient metabolism of these compounds in teleost fish. Signifcant declines in bile concentrations of naphthalene and phenanthrene metabolites in Red Snapper Lutjanus campechanus between 2011 and 2012 indicate an episodic exposure to elevated levels of hydrocarbons of petrogenic origin. The composition of PAH parent compounds and alkylated homologs in Red Snapper liver samples was highly correlated with oil collected at the Deepwater Horizon wellhead but was less coherent with other PAH sources in the NGM. The elevated 2011 prevalence of skin lesions in some NGM species was unrelated to surface salinity or temperature anomalies and was not the result of an epizootic observable in our histopathology samples but was positively correlated with PAH concentration. Thus, we fail to reject the null hypothesis that elevated skin lesion frequency is unrelated to PAH exposure from the Deepwater Horizon oil spill.
Ref: Murawski, S. A., W. T. Hogarth, E. B. Peebles, L. Barbeiri, Prevalence of External Skin Lesions and Polycyclic Aromatic Hydrocarbon Concentrations in Gulf of Mexico Fishes, Post-Deepwater Horizon, Transactions of the American Fisheries Society, 143:4, 1084-1097.
Detection of Anomalous Particles from the Deepwater Horizon Oil Spill Using the SIPPER3 Underwater Imaging Platform
The aim of this study is to investigate a data mining approach to help assess consequences of oil spills in the maritime environment. The approach under investigation is based on detecting suspected oil droplets in the water column adjacent to the Deepwater Horizon oil spill. Our method automatically detects particles in the water, classifies them and provides an interface for visual display. The particles can be plankton, marine snow, oil droplets and more. The focus of this approach is to generalize the methodology utilized for plankton classification using SIPPER (Shadow Imaging Particle Profiler and Evaluation Recorder). In this paper, we report on the application of image processing and machine learning techniques to discern suspected oil droplets from plankton and other particles present in the water. We train the classifier on the data obtained during one of the first research cruises to the site of the Deepwater Horizon oil spill. Suspected oil droplets were visually identified in SIPPER images by an expert. The classification accuracy of the suspected oil droplets is reported and analyzed. Our approach reliably finds oil when it is present. It also classifies some particles (air bubbles and some marine snow), up to 3.3%, as oil in clear water. You can reliably find oil by visually looking at the examples put in the oil class ordered by probability, in which case oil is found in the first 10% of images examined.
In search of oil seeps in the Cariaco basin using MODIS and MERIS medium resolution data
The Cariaco basin with its high sedimentation rates and active faulting make it a favorable place for active oil seeps to occur. Information on the number of seeps or their locations does not exist in the literature. Data collected from the MODIS and MERIS sensors were examined to see if they could detect oils seeps in the Cariaco basin. MODIS was able to detect 2 regions of surface slicks in 2011, however, identifying where they came from is more complicated. By identifying multiple slicks from the same region, Chen and Hu determiend that they can be traced to the same location. These sensors can be used to conservatively estimate the number of slicks as long as they are at least 3 pixels in length on the image.
On the Accuracy of SeaWiFS Ocean Color Data Products on the West Florida Shelf
Traditional field bases science surveys for large scale regions is both costly and time consuming. An alternative is to use satellite-based data products for ocean measurements. In this study, measurements of water-leaving radiance and chlorophyll-a concentrations were collected during two multiyear cruise programs and compared to the SeaWiFS standard data products. The SeaWiFS Chla-a values are significantly higher than in situ measurements in nearshore waters where there is significant freshwater discharge (CDOM loading), HAB, wind-driven sediment resuspension, and bottom reflectance. SeaWiFS Chl-a measurements beyond the 20-m isobaths were reliable, but they were consistently overestimated inshore of the 10-m isobaths.
Ref: Jennifer P. Cannizzaro, Chuanmin Hu, Kendall L. Carder, Christopher R. Kelble, Nelson Melo, Elizabeth M. Johns, Gabriel A. Vargo, and Cynthia A. Heil (2013) On the Accuracy of SeaWiFS Ocean Color Data Products on the West Florida Shelf. Journal of Coastal Research: Volume 29, Issue 6: pp. 1257 – 1272.
Sand bottom microalgal production and benthic nutrient fluxes on the northeastern Gulf of Mexico nearshore shelf
Benthic microalgal communities have been documented as being important primary producers in nearshore areas and are important to benthic feeders. However little is known about benthic micro algal production in deeper waters. Core sampling and Chl a concentrations in the sediment as opposed to cell counting has been the way to quantify production in the benthic community. Sedimtns are a source of nutrients from microbial processing of sedimented organic matter, outward flux of nutrients. In a sample site in the NE GoM, 11km SE of Pensacola Bay, light and dark sediment chambers were deployed on the seafloor Dissolved oxygen concentration and was measured via Winklers to measure production and respiration. Chl a was measured in the sediment for algal biomass, nutrients were measured. Measurements were comparable to coastal nearshore areas. Much of the continental benthic ecosystem has potential for benthic primarily production.
Ref: Allison, J. G., Wagner, M. E., McAllister, M., Ren, A, K. J., Snyder, R. A. Sand bottom microalgal production and benthic nutrient fluxes on the northeastern Gulf of Mexico nearshore shelf, Gulf and Carribbean Research, 2013, 25, 1-8