Coupling of potential habitat models with particle tracking experiments to examine larval fish dispersal and connectivity in deep water regions.

Computing Lagrangian trajectories with ocean circulation models is a powerful way to infer larval dispersal pathways and connectivity. Defining release areas and timing of particles to represent larval habitat realistically is critical to obtaining representative dispersal pathways. However, it is challenging due to spatial and temporal variability in larval density. Forward-tracking particle experiments were conducted to study larval connectivity of four species (neritic or mesopelagic) in the Gulf of Mexico's (GoM) deep-water region. A seasonal climatology coupled with predicted potential larval habitat models based on generalized additive models was used to delimit the particle dispersal origin. Two contrasting mesoscale circulation patterns were examined: (1) high Loop Current (LC) intrusion, absence of recently detached LC anticyclonic eddies (LC-ACE), and no interaction between LC-ACEs and the semi-permanent cyclonic eddy (CE) in the Bay of Campeche (BoC), and (2) limited LC intrusion, a recently detached LC-ACE, and interaction between LC-ACEs and the BoC's CE. To simulate larval transport, virtual larvae were randomly released in the potential habitats and advected for 30 days with the velocity fields of the HYbrid Coordinate Ocean Model with hourly-resolution assimilation. Potential habitat location and size played a major role in dispersal and connectivity. A greater percentage of particles were retained in potential habitats restricted to the southern BoC, suggesting lower connectivity with other GoM regions than those encompassing most of the BoC or the central Gulf. Mesoscale feature interactions in the western GoM and BoC led to greater dispersion along the western basin. By contrast, the absence of ACE-CE interaction in the BoC led to greater retention and less connectivity between the southern and northern GoM. Under high LC intrusion, particles seeded north of the Yucatan Shelf were advected through the Florida Straits and dispersed within the GoM. Coupling potential habitat models with particle experiments can help characterize the dispersal and connectivity of fish larvae in oceanic systems.

Biotic assemblages of gelatinous zooplankton in the Gulf of Mexico and adjacent waters: An evolutionary biogeographic approach.

Gelatinous zooplankton constitutes a polyphyletic group with a convergent evolutionary history and poorly known biogeographical patterns. In the Gulf of Mexico, a region with complex geological, hydrological, and biotic histories, the study of this group has been limited to taxonomical and ecological aspects. In this study, we implemented a track analysis to identify distributional patterns of gelatinous zooplankton in the Gulf of Mexico and adjacent waters based on a dataset of 6067 occurrence records corresponding to Hydrozoa, Scyphozoa, Cubozoa, Ctenophora, Chaetognatha, Thaliacea, and Appendicularia. Information was compiled from the Global Biodiversity Facility Information (GBIF) and Ocean Biodiversity Information System (OBIS) databases and peer-reviewed literature. Individual tracks were constructed by joining the minimum distance between the occurrence localities of each taxon using a minimum spanning tree algorithm. We identified generalized tracks using parsimony analysis of endemicity with progressive character elimination (PAE-PCE). The areas where different generalized tracks overlapped were considered to represent panbiogeographical nodes. Seven generalized tracks (two with nested patterns) and six panbiogeographical nodes were recognized, mainly in neritic zones. The distributional patterns of gelatinous zooplankton allowed us to identify four biogeographic areas, supporting previously proposed biogeographic schemes. Gelatinous zooplankton in the Gulf of Mexico showed a convergent spatial distribution that can be explained by vicariant and dispersal events. The historical biogeography of the gelatinous biotas of the Gulf of Mexico has been little studied compared to ecological approaches, and the lack of integrative studies considering historical patterns is evident. This type of research is fundamental to understanding the evolutionary history of natural resources from a spatial perspective, identifying sites of biodiversity and endemism, and establishing a biogeographic baseline of the region for further studies.

Deeper and stronger North Atlantic Gyre during the Last Glacial Maximum.

Subtropical gyre (STG) depth and strength are controlled by wind stress curl and surface buoyancy forcing1,2. Modern hydrographic data reveal that the STG extends to a depth of about 1 km in the Northwest Atlantic, with its maximum depth defined by the base of the subtropical thermocline. Despite the likelihood of greater wind stress curl and surface buoyancy loss during the Last Glacial Maximum (LGM)3, previous work suggests minimal change in the depth of the glacial STG4. Here we show a sharp glacial water mass boundary between 33° N and 36° N extending down to between 2.0 and 2.5 km-approximately 1 km deeper than today. Our findings arise from benthic foraminiferal δ18O profiles from sediment cores in two depth transects at Cape Hatteras (36-39° N) and Blake Outer Ridge (29-34° N) in the Northwest Atlantic. This result suggests that the STG, including the Gulf Stream, was deeper and stronger during the LGM than at present, which we attribute to increased glacial wind stress curl, as supported by climate model simulations, as well as greater glacial production of denser subtropical mode waters (STMWs). Our data suggest (1) that subtropical waters probably contributed to the geochemical signature of what is conventionally identified as Glacial North Atlantic Intermediate Water (GNAIW)5-7 and (2) the STG helped sustain continued buoyancy loss, water mass conversion and northwards meridional heat transport (MHT) in the glacial North Atlantic.

Seasonal variability in the feeding ecology of an oceanic predator.

Complementary approaches (stomach contents, DNA barcoding, and stable isotopes) were used to examine seasonal shifts in the feeding ecology of an oceanic predator, yellowfin tuna (Thunnus albacares, n = 577), in the northern Gulf of Mexico. DNA barcoding greatly enhanced dietary resolution and seasonally distinct prey assemblages were observed for both sub-adults and adults. In general, diet was characterized by ommastrephid squids and exocoetids in spring, juvenile fishes (i.e., carangids and scombrids) in summer, migratory coastal fishes during fall, and an increased consumption of planktonic prey (e.g., amphipods) in winter. Seasonal variability in bulk stable isotope values (δ13C, δ15N, and δ34S) was also observed, with low δ15N values and high δ34S values during late summer/early fall and high δ15N values (low δ34S) during late winter/early spring. Bayesian stable isotope mixing models corroborated seasonal diet shifts, highlighting the importance of oceanic nekton in spring/summer, coastal nekton during fall, and oceanic plankton during winter. Seasonal shifts in diet appeared to be influenced by prey reproductive cycles, habitat associations, and environmental conditions. Findings highlight the complex food web dynamics supporting an opportunistic oceanic predator and the importance of seasonal cycles in prey availability to predator resource utilization in open-ocean ecosystems.

Limited potexvirus diversity in eastern Gulf of Mexico seagrass meadows.

Turtlegrass virus X, which infects the seagrass Thalassia testudinum, is the only potexvirus known to infect marine flowering plants. We investigated potexvirus distribution in seagrasses using a degenerate reverse transcription polymerase chain reaction (RT-PCR) assay originally designed to capture potexvirus diversity in terrestrial plants. The assay, which implements Potex-5 and Potex-2RC primers, successfully amplified a 584 nt RNA-dependent RNA polymerase (RdRp) fragment from TVX-infected seagrasses. Following validation, we screened 74 opportunistically collected, apparently healthy seagrass samples for potexviruses using this RT-PCR assay. The survey examined the host species T. testudinum, Halodule wrightii, Halophila stipulacea, Syringodium filiforme, Ruppia maritima, and Zostera marina. Potexvirus PCR products were successfully generated only from T. testudinum samples and phylogenetic analysis of sequenced PCR products revealed five distinct TVX sequence variants. Although the RT-PCR assay revealed limited potexvirus diversity in seagrasses, the expanded geographic distribution of TVX shown here emphasizes the importance of future studies to investigate T. testudinum populations across its native range and understand how the observed fine-scale genetic diversity affects host-virus interactions.

Effects of burning and photochemical degradation of Macondo surrogate oil on its composition and toxicity.

Petroleum products in the environment can produce significant toxicity through photochemically driven processes. Burning surface oil and photochemical degradation were two mechanisms for oil removal after the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico. After burning, residual oil remains in the environment and may undergo further weathering, a poorly understood fate. Although photochemistry was a major degradation pathway of the DWH oil, its effect on burned oil residue in the environment is under studied. Here, we ignited Macondo surrogate crude oil and allowed it to burn to exhaustion. Water-accommodated fractions (WAFs) of the burn residue were created in full sunlight to determine the effects of photochemical weathering on the burned oil residue. Our findings show that increased dissolved organic carbon concentrations (DOC) for the light unburned and light burned after sunlight exposure positively correlated to decreased microbial growth and production inhibition (i.e. more toxic) when compared to the dark controls. Optical and molecular analytical techniques were used to identify the classes of compounds contributing to the toxicity in the dark and light burned and dark and light unburned WAFs. After light exposure, the optical composition between the light unburned and light burned differed significantly (p < 0.05), revealing key fluorescence signatures commonly identified as crude oil degradation products. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis showed more condensed aromatic, reduced oxygenated compounds present in the light burned than in the light unburned. FT-ICR MS also showed an increase in the percent relative abundance of carboxyl-rich alicyclic molecules (CRAM) like compounds in the light burned compared to light unburned. The increase in CRAM suggests that the composition of the light burned is more photorefractory, i.e., reduced, explaining the residual toxicity observed in microbial activity. Overall, these data indicate burning removes some but not all toxic compounds, leaving behind compounds which retain considerable toxicity. This study shows that burn oil residues are photolabile breaking down further into complex reduced compounds.

"The Hotel of 10,000 Stars": The Impact of Social-Structural Determinants of Health Among Im/migrant Shrimpers in the Gulf of Mexico.

Objectives. To identify appropriate interventions to prevent injury, we conducted a qualitative study among commercial shrimp fishermen in the Gulf of Mexico. Methods. Using qualitative and participatory research methods, including interviews, photovoice, and workplace observations in southeast Texas and the Rio Grande Valley in Texas, we examined the social‒structural dimensions that contribute to physical and psychological injury. Results. We found that multiple layers of vulnerability and danger exist among shrimpers with interacting themes: (1) recognizing risk, (2) precarious employment, and (3) psychological distress. Conclusions. Our results add to the growing body of knowledge that emphasizes the negative health impacts of underregulated, high-risk, and physically demanding work performed primarily by im/migrants. Public Health Implications. Our findings highlight the larger social‒structural conditions and context of hardships endemic to migrant labor and suggest implications for practice and policy interventions. (Am J Public Health. 2024;114(8):824-832. https://doi.org/10.2105/AJPH.2024.307696).

Climate change dominates the interannual variation of carbon export efficiency in each season in the Northern Gulf of Mexico during 1998-2011.

Carbon export efficiency is a key indicator of the capacity of biological pump, but the controlling mechanism of the efficiency remains unclear. Our findings revealed that interannual variations in seasonal carbon export efficiency are determined by direct factors including riverine nutrient fluxes, stratification, residence time. These direct factors are finally attributed to two indirect factors (human activities and climate change). We quantified the absolute contributions of direct and indirect factors to carbon export efficiency. The results showed that the carbon export efficiency in the northern Gulf of Mexico in spring (summer; autumn; winter) was driven by human activities, which accounted for an absolute contribution of 16.02% (7.20%; 4.00%; 8.49%, respectively) through riverine nutrient fluxes, and by climate change, which accounted for an absolute contribution of 33.51% (21.43%; 25.73%; 15.80%, respectively) through stratification and water residence time. Moreover, carbon export efficiency could be predicted by MEI of 8 months earlier.

MOLECULAR PHYLOGENY OF THE LEECH GENUS PONTOBDELLA (HIRUDINIDA: PISCICOLIDAE) WITH NOTES ON PONTOBDELLA CALIFORNIANA AND PONTOBDELLA MACROTHELA.

Leech specimens of the genus Pontobdella (Hirudinida: Piscicolidae) were found off the coast of the state of Oaxaca (Pacific) as well as in Veracruz and Tabasco (Gulf of Mexico), Mexico. Based on the specimens collected in Oaxaca, a redescription of Pontobdella californiana is provided, with emphasis on the differences in the reproductive organs with the original description of the species. In addition, leech cocoons assigned to P. californiana were found attached to items hauled by gillnets and studied using scanning electron microscopy and molecular approaches. Samples of Pontobdella macrothela were found in both Pacific and Atlantic oceans, representing new geographic records. The phylogenetic position of P. californiana is investigated for the first time, and with the addition of Mexican samples of both species, the phylogenetic relationships within Pontobdella are reinvestigated. Parsimony and maximum-likelihood phylogenetic analysis were based on mitochondrial (cytochrome oxidase subunit I [COI] and 12S rRNA) and nuclear (18S rRNA and 28S rRNA) DNA sequences. Based on our results, we confirm the monophyly of Pontobdella and the pantropical distribution of P. macrothela with a new record in the Tropical Eastern Pacific.

Structure and composition of microbial communities in the water column from Southern Gulf of Mexico and detection of putative hydrocarbon-degrading microorganisms.

This study assessed the bacterioplankton community and its relationship with environmental variables, including total petroleum hydrocarbon (TPH) concentration, in the Yucatan shelf area of the Southern Gulf of Mexico. Beta diversity analyses based on 16S rRNA sequences indicated variations in the bacterioplankton community structure among sampling sites. PERMANOVA indicated that these variations could be mainly related to changes in depth (5 to 180 m), dissolved oxygen concentration (2.06 to 5.93 mg L-1), and chlorophyll-a concentration (0.184 to 7.65 mg m3). Moreover, SIMPER and one-way ANOVA analyses showed that the shifts in the relative abundances of Synechococcus and Prochlorococcus were related to changes in microbial community composition and chlorophyll-a values. Despite the low TPH content measured in the studied sites (0.01 to 0.86 µL L-1), putative hydrocarbon-degrading bacteria such as Alteromonas, Acinetobacter, Balneola, Erythrobacter, Oleibacter, Roseibacillus, and the MWH-UniP1 aquatic group were detected. The relatively high copy number of the alkB gene detected in the water column by qPCR and the enrichment of hydrocarbon-degrading bacteria obtained during lab crude oil tests exhibited the potential of bacterioplankton communities from the Yucatan shelf to respond to potential hydrocarbon impacts in this important area of the Gulf Mexico.

Taxonomic distinctness and diversity patterns of a polychaete (Annelida) community on the continental shelf of the Southern Gulf of Mexico.

The spatial patterns of taxonomic diversity of annelid polychaete species from the continental shelf in the Southern Gulf of Mexico were examined in this study. We used taxonomic distinctness and its spatial variations to explore the diversity patterns and how they change between Southern Gulf of Mexico regions. In addition, using taxonomic distinctness as a dissimilarity measure and Ward's Clustering, we characterized three distinct faunal assemblages. We also investigated patterns of richness, taxonomic distinctness, and distance decay of similarity between sampling stations as a ß-diversity measure. Finally, we examined the spatial relationships between polychaete assemblages and environmental variables to test the relative importance of spatial and environmental components in annelid polychaete community structure from the Southern Gulf of Mexico. We used a combination of eigenvector-based multivariate analyses (dbMEMs) and distance-based redundancy analysis (dbRDA) to quantify the relative importance of these explanatory variables on the spatial variations of taxonomic distinctness. The significance level of spatial and environmental components to the distribution of polychaete species showed that the combined effect of spatial processes and sediment characteristics explained a higher percentage of the variance than those parameters could alone.

Spatial and Temporal Resolution of Cyanobacterial Bloom Chemistry Reveals an Open-Ocean Trichodesmium thiebautii as a Talented Producer of Specialized Metabolites.

While the ecological role that Trichodesmium sp. play in nitrogen fixation has been widely studied, little information is available on potential specialized metabolites that are associated with blooms and standing stock Trichodesmium colonies. While a collection of biological material from a T. thiebautii bloom event from North Padre Island, Texas, in 2014 indicated that this species was a prolific producer of chlorinated specialized metabolites, additional spatial and temporal resolution was needed. We have completed these metabolite comparison studies, detailed in the current report, utilizing LC-MS/MS-based molecular networking to visualize and annotate the specialized metabolite composition of these Trichodesmium blooms and colonies in the Gulf of Mexico (GoM) and other waters. Our results showed that T. thiebautii blooms and colonies found in the GoM have a remarkably consistent specialized metabolome. Additionally, we isolated and characterized one new macrocyclic compound from T. thiebautii, trichothilone A (1), which was also detected in three independent cultures of T. erythraeum. Genome mining identified genes predicted to synthesize certain functional groups in the T. thiebautii metabolites. These results provoke intriguing questions of how these specialized metabolites affect Trichodesmium ecophysiology, symbioses with marine invertebrates, and niche development in the global oligotrophic ocean.

Application of ecotoxicological tools to evaluate the quality status of mangroves under restoration in the Yucatán Peninsula, Mexico.

Ecotoxicological tools, namely biomarkers and bioassays, may provide insights on the ecological quality status of mangroves under restoration. We investigated how 1) physicochemical parameters and water bioassays using Artemia franciscana; and 2) quantification of sublethal (osmoregulatory capacity, biochemical, and oxidative stress) and individual biomarkers (density, length-weight relationship [LWR], parasitic prevalence) in the sentinel fiddler crab Minuca rapax, can improve restoration indicators in mangroves from the Yucatán Peninsula, Southern Gulf of Mexico. We showed that water quality was improved with restoration, but still presented toxicity. Regarding sublethal biomarkers, M rapax from restored areas lower osmotic regulatory capacity, higher oxidative stress, and showed lipid peroxidation. As to the individual biomarkers, the density, LWR, and the prevalence of parasites in M. rapax was higher in restored areas. The use of bioassays/biomarkers were useful as early warning indicators to better assess the health of mangroves under restoration.

Hurricanes are limiting the mangrove canopy heights in the Gulf of Mexico.

Mangrove canopy height (MCH) has been described as a leading characteristic of mangrove forests, protecting coastal economic interests from hurricanes. Meanwhile, winter temperature has been considered the main factor controlling the MCH along subtropical coastlines. However, the MCH in Cedar Key, Florida (∼12 m), is significantly higher than in Port Fourchon, Louisiana (∼2.5 m), even though these two subtropical locations have similar winter temperatures. Port Fourchon has been more frequently impacted by hurricanes than Cedar Key, suggesting that hurricanes may have limited the MCH in Port Fourchon rather than simply winter temperatures. This hypothesis was evaluated using novel high-resolution remote sensing techniques that tracked the MCH changes between 2002 and 2023. Results indicate that hurricanes were the limiting factor keeping the mean MCH at Port Fourchon to <1 m (2002-2013), as the absence of hurricane impacts between 2013 and 2018 allowed the mean MCH to increase by 60 cm despite the winter freezes in Jan/2014 and Jan/2018. Hurricanes Zeta (2020) and Ida (2021) caused a decrease in the mean MCH by 20 cm, breaking branches, defoliating the canopy, and toppling trees. The mean MCH (∼1.6 m) attained before Zeta and Ida has not yet been recovered as of August 2023 (∼1.4 m), suggesting a longer-lasting impact (>4 years) of hurricanes on mangroves than winter freezes (<1 year). The high frequency of hurricanes affecting mangroves at Port Fourchon has acted as a periodic "pruning," particularly of the tallest Avicennia trees, inhibiting their natural growth rates even during quiet periods following hurricane events (e.g., 12 cm/yr, 2013-2018). By contrast, the absence of hurricanes in Cedar Key (2000-2020) has allowed the MCH to reach 12 m (44-50 cm/yr), implying that, besides the winter temperature, the frequency and intensity of hurricanes are important factors limiting the MCH on their latitudinal range limits in the Gulf of Mexico.

Mesoscale activity drives the habitat suitability of yellowfin tuna in the Gulf of Mexico.

Yellowfin tuna, Thunnus albacares, represents an important component of commercial and recreational fisheries in the Gulf of Mexico (GoM). We investigated the influence of environmental conditions on the spatiotemporal distribution of yellowfin tuna using fisheries' catch data spanning 2012-2019 within Mexican waters. We implemented hierarchical Bayesian regression models with spatial and temporal random effects and fixed effects of several environmental covariates to predict habitat suitability (HS) for the species. The best model included spatial and interannual anomalies of the absolute dynamic topography of the ocean surface (ADTSA and ADTIA, respectively), bottom depth, and a seasonal cyclical random effect. High catches occurred mainly towards anticyclonic features at bottom depths > 1000 m. The spatial extent of HS was higher in years with positive ADTIA, which implies more anticyclonic activity. The highest values of HS (> 0.7) generally occurred at positive ADTSA in oceanic waters of the central and northern GoM. However, high HS values (> 0.6) were observed in the southern GoM, in waters with cyclonic activity during summer. Our results highlight the importance of mesoscale features for the spatiotemporal distribution of yellowfin tunas and could help to develop dynamic fisheries management strategies in Mexico and the U.S. for this valuable resource.

Harpacticoid copepods expand the scope and provide family-level indicators of the Deepwater Horizon oil spill deep-sea impacts.

The Deepwater Horizon (DWH) blowout and oil spill began on April 20, 2010 in the northern Gulf of Mexico (NGOM) deep sea (1525 m). Previous studies documented an impacted area of deep-sea floor totaling 321 km2 and were based on taxonomy at the macrofauna family level and the meiofauna major taxonomic level. In the present study, finer taxonomic resolution of the meiofauna community was employed, specifically harpacticoid copepod family biodiversity. Severe or moderate impacts to harpacticoid family biodiversity were observed at 35 of 95 sampling stations, covering an estimated area of 2864 km2, 8.9 times greater impacted area than previously reported. Sensitive and tolerant harpacticoid families were observed in the impact zone. The present study greatly expands the understanding of DWH deep-sea impacts in 2010 and demonstrates that the harpacticoid family-level response is the most sensitive indicator (reported to date) of this oil spill pollution event.

Life in the PFAS lane: The impact of perfluoroalkyl substances on photosynthesis, cellular exudates, nutrient cycling, and composition of a marine microbial community.

Perfluoroalkyl substances (PFAS) are of great ecological concern, however, exploration of their impact on bacteria-phytoplankton consortia is limited. This study employed a bioassay approach to investigate the effect of unary exposures of increasing concentrations of PFAS (perfluorooctane sulfonate (PFOS) and 6:2 fluorotelomer sulfonate (6:2 FTS)) on microbial communities from the northwestern Gulf of Mexico. Each community was examined for changes in growth and photophysiology, exudate production and shifts in community structure (16S and 18S rRNA genes). 6:2 FTS did not alter the growth or health of phytoplankton communities, as there were no changes relative to the controls (no PFOS added). On the other hand, PFOS elicited significant phototoxicity (p < 0.05), altering PSII antennae size, lowering PSII connectivity, and decreasing photosynthetic efficiency over the incubation (four days). PFOS induced a cellular protective response, indicated by significant increases (p < 0.001) in the release of transparent exopolymer particles (TEP) compared to the control. Eukaryotic communities (18S rRNA gene) changed substantially (p < 0.05) and to a greater extent than prokaryotic communities (16S rRNA gene) in PFOS treatments. Community shifts were concentration-dependent for eukaryotes, with the low treatment (5 mg/L PFOS) dominated by Coscinodiscophyceae (40 %), and the high treatment (30 mg/L PFOS) marked by a Trebouxiophyceae (50 %) dominance. Prokaryotic community shifts were not concentration dependent, as both treatment levels became depleted in Cyanobacteriia and were dominated by members of the Bacteroidia, Gammaproteobacteria, and Alphaproteobacteria classes. Further, PFOS significantly decreased (p < 0.05) the Shannon diversity and Pielou's evenness across treatments for eukaryotes, and in the low treatment (5 mg/L PFOS) for prokaryotes. These findings show that photophysiology was not impacted by 6:2 FTS but PFOS elicited toxicity that impacted photosynthesis, exudate release, and community composition. This research is crucial in understanding how PFOS impacts microbial communities.

Analysis of protected species observer data: Strengths, weaknesses, and application in the assessment of marine mammal responses to seismic surveys in the northern Gulf of Mexico 2002-2015.

Visual observation data collected by protected species observers (PSOs) is required per regulations stipulated in Notices to Lessees (NTLs) and geophysical survey Permits (Form BOEM-0328) issued to seismic operators in the Gulf of Mexico (GOM). Here, data collected by certified and trained PSOs during seismic surveys conducted between 2002-2015 were compiled and analyzed to assess utility in assessing marine mammal responses to seismic noise and effectiveness of required mitigation measures. A total of 3,886 agency-required bi-weekly PSO Effort and Sightings reports were analyzed comprising 598,319 hours of PSO visual effort and 15,117 visual sighting records of marine mammals. The observed closest point of approach (CPA) distance was statistically compared across five species groupings for four airgun activity levels (full, minimum source, ramp up, silent). Whale and dolphin detections were significantly farther from airgun array locations during full power operations versus silence, indicating some avoidance response to full-power operations. Dolphin CPA distances were also significantly farther from airguns operating at minimum source than silence. Blackfish were observed significantly farther from the airgun array during ramp up versus both full and minimum source activities. Blackfish were observed significantly closer to the airgun array during silent activities versus at full, minimum source, and ramp up activities. Beaked whales had the largest mean CPA for detection distance compared to all other species groups. Detection distances for beaked whales were not significantly differences between full and silent operations; however, the sample size was very low. Overall results are consistent with other studies indicating that marine mammals may avoid exposure to airgun sounds based on observed distance from the seismic source during specified source activities. There was geographic variability in sighting rates associated with specific areas of interest within the GOM. This study demonstrates that agency required PSO reports provide a robust and useful data set applicable to impact assessments; management, policy and regulatory decision making; and qualitative input for regional scientific, stock assessment and abundance studies. However, several improvements in content and consistency would facilitate finer-scale analysis of some topics (e.g., effort associated with specific activities, observer biases, sound field estimation) and support statistical comparisons that could provide further insight into marine mammal responses and mitigation efficacy.

Potentially toxic elements fluxes in 210Pb-dated sediment cores from a large coastal lagoon (southern Gulf of Mexico) under environmental stress.

Terminos Lagoon (TL), in the southern Gulf of Mexico, has been under intensive anthropogenic pressure (e.g., oil-industry development) since the 1970s. Historical changes in flux ratios of potentially toxic elements (PTEs; As, Cd, Cr, Cu, Ni, Pb, V, Zn) were, for the first time, assessed inside TL by using 210Pb-dated sediment cores. Sediments showed minor enrichments for Cd, Ni, Pb, and V. However, according to international benchmarks, the As, Cr, Cu, and Ni concentrations could pose a risk for benthic biota. Sedimentary processes involved in the accumulation of PTEs were identified through a chemometric approach. Increments in PTEs flux ratios concur with the recent (⁓50 years) and extensive land-use changes, particularly the transport and deposit of materials delivered by rivers. These findings are expected to be used in managing this crucial natural resource, the larger Mexican coastal lagoon ecosystem, to mitigate the effects of global change.

Temporal Variation and Persistence of Methane Emissions from Shallow Water Oil and Gas Production in the Gulf of Mexico.

Methane emissions from the oil and gas supply chain can be intermittent, posing challenges for monitoring and mitigation efforts. This study examines shallow water facilities in the US Gulf of Mexico with repeat atmospheric observations to evaluate temporal variation in site-specific methane emissions. We combine new and previous observations to develop a longitudinal study, spanning from days to months to almost five years, evaluating the emissions behavior of sites over time. We also define and determine the chance of subsequent detection (CSD): the likelihood that an emitting site will be observed emitting again. The average emitting central hub in the Gulf has a 74% CSD at any time interval. Eight facilities contribute 50% of total emissions and are over 80% persistent with a 96% CSD above 100 kg/h and 46% persistent with a 42% CSD above 1000 kg/h, indicating that large emissions are persistent at certain sites. Forward-looking infrared (FLIR) footage shows many of these sites exhibiting cold venting. This suggests that for offshore, a low sampling frequency over large spatial coverage can capture typical site emissions behavior and identify targets for mitigation. We further demonstrate the preliminary use of space-based observations to monitor offshore emissions over time.