The northern Gulf of Mexico (GOM) contains approximately 2,500 oil and gas platforms, resulting in one of the largest de facto artificial reef systems in the world. As of 2013, 1,227 additional structures had ceased to produce oil and gas and have been decommissioned and removed. While active platforms are lit by high-pressure mercury vapor lights, inactive platforms are only minimally lit for navigation. The positively phototaxic behavior of many fish species causes lit oil platforms to act as fish attraction devices, especially at night. Though a variety of fish species have been reported near these structures, changes in fish abundance, biomass, and species composition in response to artificial light regimes has not been studied thoroughly. Hydroacoustic and video surveys were conducted at two lit and three unlit oil and gas platforms located approximately 130 km off the coast of Louisiana. The goal of this study was to examine the effect of artificial lighting on fish community composition and spatial distribution during the day, night, and during crepuscular periods. Fish abundance changed with depth, season, time of day, and type of platform (lit/unlit), with blue runner (Caranx crysos) as the dominant species at both platform types. Species richness varied with season and time of day, with highest values observed in the summer and during the day. Hydroacoustic surveys were utilized to determine the spatial distribution of fish biomass (MVBS, Sv), which was largely concentrated near the structure and decreased rapidly with distance away from the platform. Platform type did not significantly impact fish biomass. Fish MVBS was highest in depth layer 3 (>60 m) and lowest in depth layer 1 (0-30 m), particularly at night. Regression trees showed a clear area of influence within 45 70 m horizontal distance around the structure, as well as fish avoidance behavior of the surface waters (< 9 m). These results suggest that though fishes are attracted to the vertical relief of the structure, they are actively avoiding the artificial light field due to nocturnal predation pressure.

Gentoo Penguins (Pygoscelis papua) are known to be generalist foragers, while Adélie (P. adeliae) and Chinstrap (P. Antarctica) tend to specialize on krill within the Western Antarctic Peninsula and South Shetland Islands, particularly during the breeding season. However, little is known on temporal consistency in diet and foraging habitat of these species, particularly at the individual level. We used stable isotope analysis (SIA) of blood and feathers to evaluate seasonal and individual foraging consistency within Adélie, Chinstrap and Gentoo Penguins breeding in the South Shetland Islands, as well as among three Gentoo Penguins populations in the Western Antarctic Peninsula and South Shetland Islands. Our results suggest that Pygoscelis penguins can differ in foraging ecology not only at the population level among species, sites and seasons, but also in the level of individual variation within populations, and in the degree of seasonal consistency within individuals. Previous dietary analyses suggest Gentoo penguins have a generalist foraging niche, which may help buffer them from recent climate-driven declines in key prey species, such as Antarctic krill (Euphausia superba). Ecological theory indicates that generalist populations fall under two different categories: Type A generalist populations exhibit large variation within individuals, and little variation between individuals, where Type B generalist populations are comprised of individual specialists, with large variation between individuals. We conducted SIA using tail feathers from Gentoo penguins at four geographically isolated breeding sites across the Scotia arc to assess individual variation in winter diets and determine the type of generalist strategies that Gentoo penguins utilize. Our results indicate the presence of individual specialization (type B generalism) within all four geographically distinct breeding colonies, with lower degrees of individual specialization in southern populations and higher degrees of individual specialization in northern populations. In addition, our results also suggest that individual specialization may be driven by prey abundance and diversity, as foraging habitat in the southern populations are marked by high abundance of Antarctic krill and low prey diversity, while the northern populations forage on a wider diversity of prey.

Common bottlenose dolphins (Tursiops truncatus; dolphins) inhabiting Mississippi Sound (MSS) in the north-central Gulf of Mexico (GMx) are considered a part of a single stock of dolphins that includes Bay Boudreau and Lake Borgne by the National Marine Fisheries Service (NMFS). MSS is bounded by the mainland (north) and several barrier islands (south). Dolphins inhabiting coastal waters directly south of the barrier islands constitute part of the Northern Coastal Stock. Abundance in MSS has been reported to fluctuate seasonally, with higher abundances of dolphins estimated in summer versus winter. Analysis of covariance was used to compare previous abundance estimates. Results indicated significantly more dolphins in the summer and when boats were used as survey platforms. To explore the possibility of finer scale distributions of dolphins within MSS based on movement patterns of individuals, from 2002 to 2005, 78 photo-identification surveys were conducted that sampled four zones in MSS: one Inner-Sound zone near Round Island, two Outer-Sound zones on the northern sides of Horn Island and Petit Bois Island and one Coastal zone outside MSS south of Petit Bois Island. Analysis of variance was used to test for main effects of zone, season (summer and winter) and presence of calves on mean group size. There were no interactions of main effects. Mean group sizes were significantly larger in Outer-Sound zones, in summer and when a calf was present in the group. Limited movement was observed between the Inner-Sound zone and the other zones. Seventy-seven individual dolphins (40%) were sighted both within and outside MSS, therefore spanning two NMFS stock units. Larger summer group sizes at Outer-Sound zones could reflect a seasonal concentration of dolphins, possibly due to zone differences that may increase prey resources or protection. The finding that some individual dolphins routinely use north and south sides of the barrier islands suggested stock boundary modification could be warranted.

Nitrogen loading in the Mississippi River from increased N fertilization of agricultural land helps to trigger an area of hypoxic water in the northern Gulf of Mexico (GOM) every summer. Louisiana wetlands can play a vital role in removing nitrate from river waters prior to discharge in the GOM. However, Louisianas wetlands have experienced significant losses in recent years. Efforts to restore wetlands include reconnecting floodplain wetlands to rivers and utilizing river diversions to re-introduce sediment to coastal wetlands. Increasing wetland connection to rivers can reduce water nitrate by expanding opportunities for nitrate reduction. I examined soil physicochemical properties, microbial characteristics, and nitrate reduction rates in a hydrologically restored bottomland hardwood forest adjacent to the Ouachita River in Louisiana. Nitrate reduction rates in the restored site were only 28% lower than those in a natural site (11.8 ± 3.4 vs 16.4 ± 8.1 mg N m-2 day-1) (P<0.1), removing approximately 48.1 metric tons of nitrate from the Ouachita River annually. Results suggest that restoring floodplain wetlands can be useful for enhancing nitrate reduction in river floodwaters, improving water quality while reducing the areal extent of hypoxia in the northern GOM. I also investigated nitrate reduction in turbulent surface water conditions resulting from sediment diversions. There is a paucity of data on nitrate loss in areas of diversions where turbulent conditions impart significant shear stress on the sediment surface, suspending fine grained sediments. Sediment cores were collected from Wax Lake Delta in Louisiana and subjected to shear stresses using a flow-through erosional microcosm system for 24 hrs. Nitrate reduction rates were determined under high, medium, and zero shear stress conditions of 0.45, 0.2, and 0 Pa, respectively. Nitrate reduction rates under high, low, and zero shear stresses were 303 ± 65.6, 186 ± 55.1, and 18.7 ± 20.2 mg N m-2 day-1, respectively (P<0.001). Rates of nitrate reduction increased significantly with an increase in shear stress, indicating that turbulent flow conditions from river diversions can significantly increase nitrate reduction rates. Results from this research can help inform modelers in predicting potential nutrient impacts of river diversions on coastal receiving basins.

Many research efforts have been made to the Mississippi coastal restoration, but long-term rheological and sedimentological experiments for sediment erosion, deposition and consolidation in diversion receiving basins are still lacking. Push cores and sediment samples were collected from West Bay, a semi-enclosed bay located on the Mississippi River Delta, and Big Mar pond, a receiving basin of the Caernarvon freshwater diversion from the Mississippi River, Louisiana. A dual-core Gust Erosion Microcosm System was used to measure time-series (0.5, 1, 2, 3, 4, 5, and 6-month after initial settling) erodibility at seven shear stress regimes (0.01-0.60 Pa) using experimental cores prepared with two initial sediment concentrations (60 and 120 kg m-3). A 230-cm tall settling column with nine sampling ports was used to measure the consolidation rates for initial sediment concentrations ranging from fluid mud (10 kg m-3) to dredge effluent (120 kg m-3) in combination with two levels of salinities (1 and 5 PSU). The erodibility of West Bay sediment decreases with increasing time of consolidation. The critical shear stress increases from 0.2 Pa after 2-month of consolidation to 0.45 Pa after 4-month of consolidation. Organic content plays a role on both sediment resuspension and consolidation, particularly for Big Mar sediment. The consolidation rates are inversely and exponentially related to initial sediment concentrations. Sediment in 1 PSU tests generally settles faster than that in 5 PSU tests. A model using a single consolidation rate was improved by adding another exponential coefficient. The improved Sanford (2008) model can better predict the consolidation profile of both rapid early settling and slow self-weight consolidation processes.

Approximately 2,300 petroleum platforms are currently operating in the Gulf of Mexico (GOM), and are estimated to provide an additional 4 to 12 km2 of artificial reef habitat. The ecological role of platforms has often been overlooked and little is known about the effect of artificial light from the active platforms on surrounding fish communities. This is the first study to address the potential impacts of artificial light on the trophic ecology of fish communities surrounding offshore platforms through gut content (GCA) and stable isotope (SIA) analyses. Red snapper (Lutjanus campechanus) were collected quarterly from February 2014 to November 2015 (n=424). Samples were taken at two active lit platforms and two unmanned unlit platforms located approximately 130 km from the coast of Louisiana. Results reveal seasonal, ontogenetic, and platform-type related differences. Although light was not a significant factor in the non-parametric GCA analysis, a higher abundance of fish prey items was observed in the diets at lit platforms. Trophic niche breadth analysis revealed significantly different niches between types of platforms. Higher δ15N at lit platforms corresponds to higher concentration of fish prey in the diets, compared to the lower δ15N associated with the abundance of tunicates in the diets at unlit platforms. A mixing model revealed that phytoplankton is the dominant carbon source in these oligotrophic, platform environments. Red snapper at lit platforms were slightly enriched in δ13C compared to those at unlit platforms. This could be attributable to the greater amount of green algae as a basal carbon source of individuals at lit platforms revealed by the mixing model, which is enriched in δ13C relative to phytoplankton. Feeding ecology of greater amberjack revealed fish to be the dominant prey items between lit and unlit platforms, and across both artificial and natural habitats. Trophic niche breadth analysis revealed significant differences between greater amberjack at lit and unlit platforms, which is likely attributable to the varying basal carbon resource. This study provides important information that may be used in the decision on installment or removal of platforms as fish habitats in the future and to assist with fisheries management.

This study applies a three-dimensional numerical model ECOM-si to simulate the circulation in the Wax Lake delta under winter cold front conditions. This model uses real topography and bathymetry of the area to reproduce tides and the circulation between December 2012 and January 2013, which captures a total of seven cold front passages. The model results demonstrate that the circulation in the Wax Lake delta area is significantly affected by the winter cold fronts. The major findings are: (1) Water fluxes in the delta distributary network are not solely propagated within the channels but also between the channels, indicating inundation process by water intrusion onto the saltmarshes, which accounts for ~25% of water flux. (2). The current flows follow the wind direction change. Along-channel current dominates while cross-channel water transport occurs at the southwester lobe during post-frontal passage. The long-term impact on sediment transport will be the lobe shift to southeastward and thus lead to a significant change in geomorphology in the delta. Water intrusion and a temporary reverse flow are observed from model results in the delta channel tip during prefrontal passage. (3) The cold-front-induced flushing event lasts 41-185 hours that flushed out 32% to 76% of total waters by seven cold front events. (4). Subtidal energy accounts for over 45% of total energy while tidal energy contributes to less than 25%. (5) Cold front-induced wind is the most important factor and dominates the hydrodynamic circulations of the Wax Lake delta in winter.

To achieve a sustainable Mississippi delta, the river must be reconnected to the delta through river diversions. However, the use of large diversions is hampered by opposition, partly due to resulting rapid decreases in salinity and the consequences of added nutrients. A large, intermittent river diversion would build land quickly, on the order of historic river crevasses, and infrequent operation would help to alleviate concerns regarding decreases in salinity and nutrient enrichment. This study examines a large, intermittent river diversion into the Maurepas Swamp, an upstream, forested wetland system. Objectives of this study were to (1) use a delta progradation model to estimate land grain trajectories and (2) combine these land building trajectories with ecosystem service valuation (ESV) to perform a cost-benefit analysis of the diversion project. Modelling results from the delta progradation model show that significant land building is possible in the Maurepas Swamp. For a 7079 m3/s diversion operated 16 weeks every 2 years, 138 km2 of subaerial land is built between 2030 and 2080 in the medium sea-level rise scenario, although significant uncertainty exists (-36%, +55%) due to uncertainty in basin parameters. ESV was conducted using benefit transfer, which produced a range of ecosystem goods and services (EGS) values - $1,365.91/acre/year (-76%, +152%) for restored swamp habitat and $145.73/acre/year (-33%, +100%) for restored marsh habitat - for disaster risk reduction, water quality improvement, recreation, and carbon sequestration. These EGS values were combined with habitat-type trajectories, cost estimates of the river diversion, and several discount rates to perform the cost-benefit analysis. Assuming a cost of $1.75 billion, a positive marginal benefit is realized at discount rates of about -1%, -1.6%, and -2.1% in the low, medium, and high SLR scenarios, respectively. In interpreting these results, it is important to be aware that benefit transfer is limited by the quality and quantity of relevant studies, and this study constitutes a very geographically specific usage of benefit transfer. Only a subset of the EGS provided by the Maurepas Swamp were analyzed, due to limited primary valuations within Louisiana, and error is accrued in transferring studies out of location and context.

The northern Gulf of Mexico and the coastal estuaries of south Louisiana have a history of contaminated sediments and their associated human and environmental impacts. Hydrocarbon chemical pollutants within five major estuaries of the Mississippi River watershed and three offshore shoaling regions were assessed. Ten polycyclic aromatic hydrocarbons (PAHs) and three toxic equivalencies served as benchmark toxicants to investigate the impacts to sediments collected in years 2012 to 2014. The samples were analyzed using gas chromatography/mass spectroscopy (GC/MS) methods to determine the concentrations of pollutants within the sediments. Relationships between the measured pollutants and associated environmental conditions, including salinity, organic matter, temperature, dissolved oxygen, and temporal and spatial variables, were determined. The most important physiochemical variables affecting PAH concentrations were sediment moisture and organic matter content. Year had a significant and negative effect on four of the ten quantified PAHs with concentrations decreasing over time. Eight of the thirteen measured constituents had concentrations that were significantly different between inshore and offshore sediments. Seven of the ten quantified constituents were significantly affected by seasonal variations; the fall season demonstrated significantly lower concentrations of the pollutants as compared to the spring and the spring season showed significantly higher concentrations of the pollutants as compared the summer. Six of the thirteen measured constituents were significantly different in terms of quantified concentrations of the pollutants between oiled and non-oiled sediment samples, based on Deepwater Horizon oil intrusion. In each instance, the concentrations of the pollutants in the sediments were greater at oiled sampling stations as compared to non-oiled locations. The Atchafalaya River transect had the highest predicted concentrations for nine of the thirteen measured constituents and seven out of thirteen showed offshore contaminant deposition at Ship Shoal due to the discharge of the Atchafalaya River. Lake Pontchartrain was the least polluted transect with the lowest predicted concentrations for seven of the thirteen constituents. This comprehensive research provides spatial and temporal data crucial for risk assessment and decision making concerning sediments in the Mississippi River delta ecosystem.

Plankton are an integral component to marine ecosystems globally, as they are the foundation of the marine food web. The offshore Gulf of Mexico (GoM) is an area which supports large fisheries, as well as a growing offshore oil and gas industry. The event of the Deepwater Horizon oil spill disaster accentuated the historical lack of data characterizing plankton communities in these waters. Overall, the majority of plankton research in the GoM has concentrated on the shelf waters, focusing primarily on larval fish and eggs, leaving the offshore plankton communities understudied. These prior studies employed nets as the primary method for sample collection, thus they are inherently coarse in their spatial resolution. Extrusion through the meshes of nets causes fragile plankton, and delicate particles (marine snow) to be under sampled. Using the Digital Autonomous Video Plankton Recorder (DAVPR), spatially detailed data on major plankton taxa, and marine snow, as well as coincident environmental data (temperature, salinity, density, dissolved oxygen, and chlorophyll), were collected at nine stations in the deepwater (>300m) GoM during spring (April May) 2011. Remotely sensed satellite data were acquired to visualize the regional distribution of sea surface properties for elevation, temperature, and chlorophyll concentration. Plankton and marine snow distributions in the GoM offshore waters were correlated to the distribution of environmental parameters in both the vertical and horizontal. Two prominent hydrographic features that were present during spring 2011 study had the most substantial impact on plankton communities. A single station (S5), located furthest to the north was influenced by low-salinity, nutrient rich, shelf water at its surface to ~25m depth, which greatly enhanced the biological activity at this site. The southeastern stations (S7, S8, and S9) were located along the frontal boundary of the Loop Current. In these sites where the LC brought higher salinity, denser, oligotrophic water to the upper 200m of the water column, the cyanobacterium Trichodesmium was strongly associated. The stations located outside the hydrographically unique stations (S5, S7, S8, and S9) had plankton communities that were largely similar. Plankton communities were characterized as being specific to stations sharing a similar environmental structure.