Northern Gulf Of Mexico Research Articles

A roadmap to the Co-production of a decision support tool for coastal ecosystems

Coastal ecosystems are complex and often support a broad spectrum of functions with competing objectives. In addition to their ecological value, they offer socio-economic benefits (i.e., ecosystem services) to coastal communities. One potential way to help address this complexity is to use decision support systems to help natural resources managers understand system dynamics and evaluate strategies to maintain the health and integrity of these ecosystems. This paper presents a roadmap and detailed application of co-production strategies where managers and researchers are fully engaged in a collaborative manner in the design of a decision support tool for coastal ecosystems. It also emphasizes the importance of capturing end-users’ (i.e., natural resource managers) priorities to refine the conceptual design of the decision support tool, while maintaining a sound scientific and modeling framework. The case study presented here centers on the Northern Gulf of Mexico, but the concept can be exported globally to other systems. This effort highlights foundational co-production strategies, including transdisciplinary team assembly, a knowledge sharing workshop, Toolbox Dialogue Initiative workshops to facilitate working across disciplines, core team and focus group meetings, and design charrettes. Further, this paper articulates the benefits and difficulties of executing a co-production process through virtual collaborations.

Particulate organic carbon in the deep-water region of the Gulf of Mexico

Ocean eddies play a major role in lateral and vertical mixing processes of particulate organic carbon (POC), as well as in the transport of heat, salinity, and biogeochemical tracers. In the open waters of the Gulf of Mexico (GoM), however, there are limited observations to characterize how these mesoscale structures affect the spatial distribution of POC in the upper water column, which is important for organic matter cycling and export. We present the distribution patterns of POC relative to mesoscale features throughout the water column in the deep-water region of the GoM during three oceanographic cruises held during the summer months of 2015, 2016, and 2017. Samples were collected under well-stratified upper ocean conditions, which allowed us to assess the spatial and temporal distribution of POC as a function of non-steric sea surface height, density, apparent oxygen utilization, and chlorophyll fluorescence. We further explored the variability of integrated surface layer POC concentrations at stations located within the cores and the edges of cyclonic and anticyclonic eddies, and those collected outside these structures. Although our results indicate mesoscale eddies modulate several important physical and biogeochemical variables and POC concentrations in the upper ocean, these features do not fully explain the spatial distribution of POC concentrations throughout the deep-water region of the GoM. Relatively lower POC concentrations were observed in the border of the cyclonic and the center of the anticyclonic eddies, in contrast to the relatively higher POC concentrations at the center of the cyclonic and the border of anticyclonic eddies. We observed high variability in POC concentration variability outside mesoscale structures, which may be attributed to other processes such as upwelling over the shelves, and the contribution by rivers during the summer especially in the northern and southern GoM.

Life Histories Vary with Primary Productivity in the Northern Gulf of Mexico

Human activities have increased nutrient delivery to aquatic ecosystems around the world, spurring primary productivity, and leading to the establishment and expansion of oxygen-limited “dead zones.” How will marine animals respond to these changing conditions? To address that question, we take a space-for-time approach and compare the traits of different marine invertebrates along a primary productivity gradient in the northern Gulf of Mexico. Previous studies have found that life history traits can be sensitive to prevailing environmental conditions. Using Holocene death assemblages collected from -20 meters offshore Alabama and Florida, we test the hypothesis that bivalve egg size, and bryozoan reproductive mode, vary with primary productivity. Based on previous studies, we expect populations in areas with an abundance of food to exhibit the following characteristics: 1) cupuladriid bryozoans will exhibit greater frequencies of clonal to aclonal reproduction; and 2) bivalves will produce smaller eggs due to greater juvenile survivorship and fecundity selection. We found that Discoporella depressa colonies show low frequencies of clonal reproduction overall, but that percent clonality was greater in coastal Alabama than Florida. Cupuladria colonies showed higher proportions of clonal reproduction, whereas Reussirella doma colonies exhibited exclusively aclonal reproduction. Egg size is positively correlated with the earliest stage of larval shell growth (PI size) in marine bivalves. Nucula proxima larval shell size varied inversely with primary productivity; larval shells were larger in Florida than Alabama. Preliminary live-dead results in both regions show limited evidence of change over time, in contrast with previous analyses of other bivalve species in the region. These space-for-time case studies highlight ways in which benthic marine invertebrates may respond to future anthropogenic driven changes in primary production in the coastal ocean.

Shell Microstructure as an Indicator of Changing Environmental Conditions in Coastal Oceans

Ocean ecosystems are undergoing pronounced changes in temperature and chemistry. Biomineralizing animals, such as mollusks, that produce calcium carbonate shells can be sensitive to these changes, and this may be reflected in the microstructure of their shells. Shell microstructure potentially offers conservation paleobiologists an additional tool for assessing spatiotemporal changes in environmental conditions resulting from human activities. Previous work suggests that environmental factors, such as temperature and pH, can affect how mollusks build their shells. Certain mollusks continuously lay down tablets of nacre on the interior of their shells, and the thickness of these tablets may reflect the temperature of the environment in which the organism lived. We have been investigating spatial and temporal variation in tablet thickness in two groups of marine mollusks. Our first case study focuses on a variety of present-day abalone species along a temperature gradient. Data were collected from individuals raised in aquaculture at controlled temperatures, as well as wild-grown individuals from different latitudes in the Pacific Ocean. Our second case study focuses on the marine bivalve Nucula proxima from the northern Gulf of Mexico. Live and dead Nucula proxima specimens were collected from 20 meters water depth offshore Louisiana and Alabama; radiocarbon analyses indicate that these specimens represent both present-day and pre-Industrial populations. Our preliminary results show: 1) little variation in tablet thickness among abalone grown in aquaculture at different temperatures, suggesting that fine scale variation in temperature has little effect on abalone microstructure; and 2) an increase in tablet thickness during the past 250 years for N. proxima offshore Louisiana, but little change in N. proxima microstructure in coastal Alabama over past centuries.

Temporal variability of microbial response to crude oil exposure in the northern Gulf of Mexico

Oil spills are common occurrences in the United States and can result in extensive ecological damage. The 2010 Deepwater Horizon oil spill in the Gulf of Mexico was the largest accidental spill recorded. Many studies were performed in deep water habitats to understand the microbial response to the released crude oil. However, much less is known about how planktonic coastal communities respond to oil spills and whether that response might vary over the course of the year. Understanding this temporal variability would lend additional insight into how coastal Florida habitats may have responded to the Deepwater Horizon oil spill. To assess this, the temporal response of planktonic coastal microbial communities to acute crude oil exposure was examined from September 2015 to September 2016 using seawater samples collected from Pensacola Beach, Florida, at 2-week intervals. A standard oil exposure protocol was performed using water accommodated fractions made from MC252 surrogate oil under photo-oxidizing conditions. Dose response curves for bacterial production and primary production were constructed from 3H-leucine incorporation and 14C-bicarbonate fixation, respectively. To assess drivers of temporal patterns in inhibition, a suite of biological and environmental parameters was measured including bacterial counts, chlorophyll a, temperature, salinity, and nutrients. Additionally, 16S rRNA sequencing was performed on unamended seawater to determine if temporal variation in the in situ bacterial community contributed to differences in inhibition. We observed that there is temporal variation in the inhibition of primary and bacterial production due to acute crude oil exposure. We also identified significant relationships of inhibition with environmental and biological parameters that quantitatively demonstrated that exposure to water-soluble crude oil constituents was most detrimental to planktonic microbial communities when temperature was high, when there were low inputs of total Kjeldahl nitrogen, and when there was low bacterial diversity or low phytoplankton biomass.

Structural architecture and evolution of eastern Mississippi Canyon, northern gulf of Mexico

3-D, depth-migrated seismic data are used to evaluate the structural architecture and evolution of eastern Mississippi Canyon, northeastern Gulf of Mexico. The W-dipping base of the Louann salt is mostly unfaulted, such that basement faults did not influence Late Jurassic to Recent deformation. Instead, the suprasalt evolution was driven by a combination of lateral (gravity-driven) and vertical (differential loading) forces that varied in importance and direction over time. Salt movement was initiated in the Late Jurassic by SW-directed, convergent gravity gliding on an arcuate margin. This resulted in both contractional thrust faults and folds and dome-and-basin structures that set up the initial configuration of minibasins, salt plateaus, and early diapirs. The minibasins evolved as either turtle structures or expulsion-rollover structures, with the distribution of the two defining a convergent Mesozoic paleo-slope and age-equivalent basin floor. Gravity-driven deformation waned and differential loading gradually became more important during this time. The relative interplay between the two drivers reversed again during the Miocene due to a combination of progressive welding of the Louann salt and an eastward shift of Miocene deltaic shelf edges updip of the study area. The latter triggered SSE-directed gravity spreading, with most of the resultant extension and contraction located in more proximal and distal areas, respectively. The study area was mostly in the translational domain, which was bounded by a zone of sinistral strike-slip deformation downdip of the lateral edges of the deltaic depocenters. Miocene salt structures defined two provinces: a proximal domain characterized by counterregional feeders and basinward-flowing salt sheets; and a distal domain with vertical feeders and radially-spreading allochthonous salt. The boundary between the two marked the Miocene toe of slope. Lessons derived from the study area can be applied to help understand the more complex structures and evolution farther west in the northern Gulf of Mexico.

Investigating beaked whale’s regional habitat division and local density trends near the Deepwater Horizon oil spill site through acoustics

Pre-spill and post-spill passive acoustic data collected by multiple fixed acoustic sensors monitoring about 2400 km2area to the west of the Deepwater Horizon oil spill in the northern Gulf of Mexico (GoM) were analyzed to understand long term local density trends and habitat use by different species of beaked whales. The data were collected in the Mississippi Valley/Canyon area between 2007 and 2017. A multistage algorithm based on unsupervised machine learning was developed to detect and classify different species of beaked whales and to derive species- and site-specific densities in different years before and after the oil spill. The results suggest that beaked whales continued to occupy and feed in these areas following the Deepwater Horizon oil spill thus raising concerns about (1) potential long-term effects of the spill on these species and (2) the habitat conditions after the spill. The average estimated local density of Cuvier’s beaked whales at the closest site, about 16 km away from the spill location showed statistically significant increase from July 2007 to September 2010, and then from September 2010 to 2015. This is the first acoustic study showing that Gervais’ beaked whales are predominantly present at the shallow site and that Cuvier’s species dominate at two deeper sites, supporting the habitat division (ecological niche) hypothesis. The findings call for continuing high-spatial-resolution long-term observations to fully characterize baseline beaked whale population and habitat use, to understand the causes of regional migrations, and to monitor the long-term impact of the spill.

Macrofauna abundance and diversity patterns of deep sea southwestern Gulf of Mexico

The diversity and distribution of macrofaunal communities in the deep-sea bottoms of Gulf of Mexico (GoM) Mexican waters are poorly known compared to the northern GoM. This study was designed to contribute to the knowledge of macrofauna communities through (i) evaluate the taxonomic composition of macrofauna communities at major taxa level, and (ii) analyze the spatial distribution patterns in the deep sea of the southwestern GoM. Benthic macrofauna composition was analyzed in a large geographical area (92.67°–96.70° W 18.74°–23.04° N) and bathymetric gradient (185-3740 m depth). Samples were collected on board the R/V Justo Sierra (Universidad Nacional Autónoma de México) with a Reineck-type box corer during the oceanographic cruises SOGOM-3 and SOGOM-4 carried out on April 21–May 15, 2017, and on August 29–September 20, 2018, respectively. Thirteen environmental parameters were measured (among them, depth, salinity, temperature, O2, sediment grain size, hydrocarbons, and organic matter). Twenty-five taxa were registered in SOGOM 3 (2315 individuals) all of which were observed in SOGOM 4 (1721 individuals) with exception of the mollusk Class Solenogastres. The average abundance (ind. m-2) registered was 517 (range: 150-1388 ind. m-2), and 347 (range: 38-1088 ind. m-2) for SOGOM 3, and SOGOM 4, respectively. In SOGOM 3 Polychaeta, Nematoda, Amphipoda, Tanaidacea, and Bivalvia contributed with 75% of the total abundance, which were also the most abundant in SOGOM 4 representing 82% of total macrofauna abundance. Highest abundance was registered to the south of the study area near the coast, and the lowest one was found in deeper areas. Macrofauna abundance decreased with depth in both cruises. High diversity values were registered at intermediate depths in the south and west zones of the study area. Both cruises separated in a nMDS analysis. During SOGOM 3 dissolved oxygen, aromatic hydrocarbons, and organic matter (%) were the environmental variables related to macrofauna whereas, in SOGOM 4, depth was the most important one. This study fills a gap in the knowledge of diversity and distribution of macrofaunal communities of the deep-sea bottoms of a large area covering the whole bathymetric range of southern Gulf of Mexico and provides a baseline useful to compare with polluted areas and for assessing the impact of chronic pollution and/or potential oil spill accidents.

Ontogenetic habitat partitioning among four shark species within a nursery ground

Context Nursery areas provide refuge from predators, rich foraging grounds, and physical conditions conducive to growth and development of juvenile inhabitants. Specifically, the Mississippi Sound in the northern Gulf of Mexico is likely a nursery ground for multiple large and small coastal sharks. Aims and methods Using over a decade of shark survey catch data, we employed habitat modelling approaches to identify preferred environmental conditions and spatial distribution, and quantify core habitat overlap within the Mississippi Sound for young-of-year (YOY), juvenile and adult life stages of four coastal shark species. Results YOY Atlantic sharpnose (Rhizoprionodon terraenovae), blacktip (Carcharhinus limbatus) and finetooth (Carcharhinus isodon) sharks showed a preference for a combination of shallow, warm, low salinity, low dissolved oxygen and turbid waters. Corresponding to shared environmental preferences, spatial distributions of YOY sharks showed a high degree of overlap, particularly in the northern portion of the Mississippi Sound where few adult sharks were observed, suggesting that these life stages partition themselves to avoid predation. Conclusion and implications With a continued rise in US coastal shark populations, we hope this study can help further refine essential fish habitat for these coastal species and provide a framework analysis that can be used to understand habitat partitioning in other regions.

Biogeographic patterns of hydrozoans in the Gulf of Mexico and adjacent waters: biological assemblages, beta diversity, and endemism

The biogeography of hydrozoans encompasses a broad scope of study that involves various challenges due to their diverse distributional strategies and life cycle characteristics. This work aims to study the biogeographic patterns of hydrozoans in the Gulf of Mexico. Occurrence records on hydrozoans were compiled through the Global Biodiversity Facility Information database and peer-reviewed literature. Biogeographic patterns were addressed through (1) the identification of biological assemblages, using hierarchical clustering with contiguity constraint; (2) the decomposition of beta diversity into species replacement, nestedness, and local contribution to beta diversity (LCBD); and (3) the identification of areas of endemism with a parsimony analysis of endemicity (PAE). The northern Gulf of Mexico and the Yucatán Peninsula contain a large hydrozoan assemblage that splits into smaller groups at different levels, characterized by species replacement and high LCBD values. By contrast, the southern Gulf of Mexico contains a homogenous assemblage, which exhibits low LCBD values and contributes strongly to nestedness. PAE identified 19 areas of higher-level endemism, concentrated mainly in shelf zones of the Yucatán and Florida peninsulas. The distribution patterns of hydrozoans in the Gulf of Mexico may be shaped by the life cycle characteristics of the taxa and the geological history of the region, relating either to neritic or oceanic zones. The northern Gulf reflects a heterogeneous biological composition with a complex biogeographical history, which makes this area of particular interest for future studies, as it likely represents a transition zone. This premise must be corroborated in the future.

Fish community characterization of mid-shelf and shelf- edge mesophotic coral ecosystems in the expanded Flower Garden Banks National Marine Sanctuary

The mid to outer continental shelf in the northern Gulf of Mexico is composed of a patchy distribution of coral and rock reefs designated high priority for marine protection. To better understand the influence of deepwater habitat on fish community dynamics and conservation needs, we compared altiphotic-mesophotic transition (20– 40 m), upper mesophotic (40–60 m), and middle mesophotic (60–80 m) fish communities between mid-shelf (Sonnier Bank) and outer-shelf (McGrail Bank) banks from before their inclusion into the Flower Garden Banks National Marine Sanctuary. Surveys performed over two years with a remotely operated vehicle indicated that each bank and depth zone had distinct fish communities. Both banks were dominated by planktivores and piscivores, with an increase in depth specialists (e.g., deepwater anthiids and serranids) at the deeper zones surveyed, particularly in middle mesophotic depths at McGrail. An increased frequency of snappers, groupers, and amberjack was observed at Sonnier Bank, predominately in mesophotic depths, indicating the Sonnier Mesophotic Coral Ecosystem as either a hotspot or potential refuge for meso- and apex predators. This study fills a temporal gap in fish community dynamics of these two banks, serving to create a more continuous dataset available to assist in conservation assessments of the Flower Garden Banks National Marine Sanctuary.

Epiphytic diatom production on the seagrass Thalassia testudinum in northern Gulf of Mexico

Epiphytic diatom production on the seagrass Thalassia testudinum in northern Gulf of Mexico

A Miocene Nannofossil Biostratigraphic Case Study: Alaminos Canyon Block 627 and Mississippi Canyon Block 555, and Sedimentation Rates in the Gulf of Mexico

The Miocene sediments of 2 deep—water boreholes from the northern Gulf of Mexico, from Alaminos Canyon (AC) Block 627 and Mississippi Canyon (MC) Block 555, have been biostratigraphically analyzed using calcareous nannofossils, revealing changes in sedimentation rates and depositional environments between these 2 areas. High nannofossil abundance values and low sedimentation rates generally recorded in the Alaminos Canyon region suggest a condensed section during much of the Miocene, associated with a basinal environment. Mississippi Canyon exhibits lower nannofossil abundance and higher sedimentation rates compared to Alaminos Canyon during the majority of the Miocene. Increased sediment volumes are largely attributed to input from the Mississippi River. Sedimentation rate was calculated for both sites. In the AC Block 627 borehole, sedimentation rate ranged from 13 to 107 m/million years (my), and in the MC Block 555 borehole, it varied from 11 to 914 m/my. One major anomaly was a low observed sedimentation rate in the lowest portion of the section at MC Block 555, in the interval defined between the extinctions of Triquetrorhabdulus carinatus and Dictyococcites bisectus. This may reflect a hiatus or possible fault which has shortened the section.

Causes of death and pathogen prevalence in bottlenose dolphins Tursiops truncatus stranded in Alabama, USA, between 2015 and 2020, following the Deepwater Horizon oil spill.

Between 2010 and 2014, an unusual mortality event (UME) involving bottlenose dolphins Tursiops truncatus occurred in the northern Gulf of Mexico, associated with the Deepwater Horizon oil spill (DWHOS). Cause of death (COD) patterns in bottlenose dolphins since then have not been analyzed, and baseline prevalence data for Brucella ceti and cetacean morbillivirus, 2 pathogens previously reported in this region, are lacking. We analyzed records from bottlenose dolphins stranded in Alabama from 2015 to 2020 with necropsy and histological findings to determine COD (n = 108). This period included another UME in 2019 associated with prolonged freshwater exposure. A subset of individuals that stranded during this period were selected for molecular testing for Brucella spp. and Morbillivirus spp. Causes of death for all age classes were grouped into 6 categories, including (1) human interaction, (2) infectious disease, (3) noninfectious disease (prolonged freshwater exposure and degenerative), (4) trauma, (5) multifactorial, and (6) unknown. Two additional categories unique to perinates included fetal distress and in utero pneumonia. Human interaction was the most common primary COD (19.4%) followed closely by infectious disease (17.6%) and noninfectious disease (freshwater exposure; 13.9%). Brucella was detected in 18.4% of the 98 animals tested, but morbillivirus was not detected in any of the 66 animals tested. Brucella was detected in some moderately to severely decomposed carcasses, indicating that it may be beneficial to test a broad condition range of stranded animals. This study provides valuable information on COD in bottlenose dolphins in Alabama following the DWHOS and is the first to examine baseline prevalence of 2 common pathogens in stranded animals from this region.

Diel patterns of depth use and swimming activity of post-release greater amberjack (Seriola dumerili) in the northern Gulf of Mexico

Diel patterns of depth use and swimming activity of post-release greater amberjack (Seriola dumerili) in the northern Gulf of Mexico

Using autonomous recording units to detect individual marsh birds in the Northern Gulf of Mexico.

Marsh birds are highly elusive and select wetland habitats that are difficult to navigate, as well as easily damaged by human observers. Autonomous recording units (ARUs) have been used to determine presence or absence of marsh bird species, but little is known about distance effects on detection probability. Therefore, our objectives were to 1.) evaluate if ARUs can be used to accurately count three marsh bird species (e.g., Clapper Rail, Least Bittern, Seaside Sparrow), 2.) estimate detection probability curves based on ARU recordings, and 3.) determine the area surveyed by the ARU for the three species. We arranged ARUs to record calls from our marsh bird species broadcasted from Bluetooth speakers at fixed distances. We replicated natural calling scenarios by playing calls in different number combinations of individuals, ranging from 1 to 10 birds. To reduce interference from real bird vocalizations, we conducted our experiment in a recently burned pine savanna habitat that had similar herbaceous vegetation structure to the coastal emergent wetland habitats preferred by these species in southern Mississippi. We used Raven Pro bioacoustics software to produce sonogram images of the broadcasted calls to count individuals in each recording. Detection probability of each species by distance was calculated in program R. Results showed that ARUs may be useful for counting individuals at close distances for some species (< 100m), but most counts biased low. In Clapper Rails and Least Bitterns, count accuracy decreased between 100 and 125 meters from the ARU but closer (50-100 meters) for Seaside Sparrows. There was also a significant decline in count accuracy with increasing chorus size. With further study and advancing technology, ARUs may be able to supplement marsh bird surveys and limit logistical issues.

Size-Mediated Sea Turtle Behavioral Responses at Artificial Habitats in the Northern Gulf of Mexico.

Our understanding of size-specific sea turtle behavior has lagged due to methodological limitations. However, stereo-video cameras (SVC) are an in-water approach that can link body-size and allow for relatively undisturbed behavioral observations. In this study, we conducted SVC dive surveys at local artificial reefs, piers, and jetties in the northern Gulf of Mexico (nGOM) from May 2019 to August 2021. Using SVCs, we measured sea turtle straight carapace length, documented behaviors, and quantified wariness by assessing minimum approach distance (MAD). In green sea turtles (Chelonia mydas), the observed MAD ranged from 0.72 to 5.99 m (mean 2.10 m ± 1.10 standard deviation (SD), n = 73). For loggerhead sea turtles (Caretta caretta), the MAD ranged between 0.93 and 3.80 m (mean 2.12 m ± 0.99 SD, n = 16). Kemp's ridley sea turtles (Lepidochelys kempii) were similar to loggerheads, and MAD ranged from 0.78 to 3.63 m (mean 2.35 m ± 0.99 SD, n = 8). We then evaluated what biological factors could impact the MAD observed by species, but we excluded Kemp's ridleys as the sample size was small. Using a linear mixed model and model selection based on AICc, the top ranked model for both green and loggerhead sea turtles included SCL as the most important factor influencing MAD. MAD did not vary with habitat type for either species. Our results showed that larger individuals, regardless of species, have a greater wariness response, becoming startled at greater distances than smaller individuals. The findings of our study support the use of SVC as an accessible, non-invasive tool to conduct ecologically relevant in-water surveys of sea turtles to link behavioral observations to body size.

Effects of varying types and amounts of herbivory and nutrient enrichment on a tropicalizing seagrass meadow

Climate change is impacting marine ecosystem community dynamics on a global scale. While many have assessed direct effects of climate change, indirect effects on marine ecosystems produced by biotic interactions remain poorly understood. For example, warming-induced range expansions and increased consumption rates of herbivores can lead to significant and unexpected changes in seagrass-dominated ecosystems. To better understand the threats tropicalization presents for the functioning of turtlegrass (Thalassia testudinum) meadows, we focused on the extensive turtlegrass beds of St. Joseph Bay, Florida in the northern Gulf of Mexico, a location with increasing numbers of tropically-associated green turtles. Our goals were to investigate experimentally how different grazing rates (natural and simulated),including high levels reflective of green turtle herbivory, coupled with nutrient supply, might alter turtlegrass structure and functioning in a higher latitude, subtropical turtlegrass meadow. We found that 4 months of varying levels of herbivory did not affect turtlegrass productivity, while 7 months of herbivory reduced percent cover, and 10 months reduced shoot density. Nutrient additions had few important effects. Ten months into the study, a massive recruitment of the herbivorous sea urchin (Lytechinus variegatus), whose densities reached 19 urchins/m2 completely overgrazed our study area and a large portion of the lush turtlegrass meadows of St. Joseph Bay. While local turtlegrass overgrazing had been previously noted at these urchin densities, a total loss of seagrass in such a large area has rarely ever been recorded. Overgrazing of the kind we observed, likely a result of both urchin and increasing green turtle grazing, can result in the loss of many key ecosystem services. As tropicalization continues, understanding how changes in biotic interactions, such as increased herbivory, affect higher latitude seagrass meadows will be necessary for their proper management and conservation.

Metagenomics and metatranscriptomics reveal broadly distributed, active, novel methanotrophs in the Gulf of Mexico hypoxic zone and in the marine water column.

The northern Gulf of Mexico (nGOM) hypoxic zone is a shallow water environment where methane, a potent greenhouse gas, fluxes from sediments to bottom water and remains trapped due to summertime stratification. When the water column is destratified, an active planktonic methanotrophic community could mitigate the efflux of methane, which accumulates to high concentrations, to the atmosphere. To investigate the possibility of such a biofilter in the nGOM hypoxic zone we performed metagenome assembly, and metagenomic and metatranscriptomic read mapping. Methane monooxygenase (pmoA) was an abundant transcript, yet few canonical methanotrophs have been reported in this environment, suggesting a role for non-canonical methanotrophs. To determine the identity of these methanotrophs, we reconstructed six novel metagenome-assembled genomes (MAGs) in the Planctomycetota, Verrucomicrobiota and one putative Latescibacterota, each with at least one pmoA gene copy. Based on ribosomal protein phylogeny, closely related microbes (mostly from Tara Oceans) and isolate genomes were selected and co-analyzed with the nGOM MAGs. Gene annotation and read mapping suggested that there is a large, diverse and unrecognized community of active aerobic methanotrophs in the nGOM hypoxic zone and in the global ocean that could mitigate methane flux to the atmosphere.

Migratory Movements and Home Ranges of Geographically Distinct Wintering Populations of a Soaring Bird

Migratory soaring birds exhibit spatiotemporal variation in their circannual movements. Nevertheless, it remains uncertain how different winter environments affect the circannual movement patterns of migratory soaring birds. Here, we investigated annual movement strategies of American white pelicans Pelecanus erythrorhynchos (hereafter, pelican) from two geographically distinct wintering grounds in the Southern and Northern Gulf of Mexico (GOM). We hypothesized that hourly movement distance and home range size of a soaring bird would differ between different geographic regions because of different thermals and wind conditions and resource availability. We calculated average and maximum hourly movement distances and seasonal home ranges of GPS-tracking pelicans. We then evaluated the effects of hour of the day, seasons, two wintering regions in the Southern and Northern GOM, human footprint index, and relative pelican abundance from Christmas Bird Count data on pelican hourly movement distances and seasonal home ranges using linear mixed models and generalized linear mixed models. American white pelicans moved at greatest hourly distance near 1200 h at breeding grounds and during spring and autumn migrations. Both wintering populations in the Northern and Southern GOM exhibited similar hourly movement distances and seasonal home ranges at the shared breeding grounds and during spring and autumn migrations. However, pelicans wintering in the Southern GOM showed shorter hourly movement distances and smaller seasonal home ranges than those in the Northern GOM. Hourly movement distances and home ranges of pelicans increased with increasing human footprint index. Winter hourly movements and home ranges of pelicans differed between the Northern and Southern GOM; however, the winter difference in pelican movements did not carry over to the shared breeding grounds during summers. Therefore, exogenous factors may be the primary drivers to shape the flying patterns of migratory soaring birds.