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Wave‐supported fluid mud (WSFM) plays an important role in sediment downslope transport on the continental shelves. In this study, we incorporated WSFM processes in the wave boundary layer (WBL) into the Community Sediment Transport Modeling System (CSTMS) on the platform of the Coupled Ocean‐Atmosphere‐Wave‐and‐Sediment Transport modeling system (COAWST). The WSFM module was introduced between the bottommost water layer and top sediment layer, which accounted for the key sediment exchange processes (e.g., resuspension, vertical settling, diffusion, and horizontal advection) at the water‐WBL and WBL‐sediment bed boundaries. To test its robustness, we adapted the updated model (CSTMS + WBL) to the Atchafalaya shelf in the northern Gulf of Mexico and successfully reproduced the sediment dynamics in March 2008, when active WSFM processes were reported. Compared with original CSTMS results, including WSFM module weakened the overall intensity of sediment resuspension, and the CSTMS + WBL model simulated a lutocline between the WBL and overlying water due to the formation of WSFM. Downslope WSFM transport resulted in offshore deposition (>4 cm), which greatly changed the net erosion/deposition pattern on the inner shelf off the Chenier Plain. WSFM flux was comparable with suspended sediment flux (SSF) off the Atchafalaya Bay, and it peaked along the Chenier Plain coast where wave activities were strong and the bathymetric slope was steep. The influence of fluvial sediment supply on sediment dynamics was limited in the Atchafalaya Bay. Sensitivity tests of free settling, flocculation, and hindered settling effects suggested that sediments were transported further offshore due to reduced settling velocity in the WBL once fluid mud was formed. Although sediment concentration in the WBL was sensitive to surface sediment critical shear stress, cohesive bed behavior was less important in WSFM dynamics when compared with strong hydrodynamic during cold fronts. Plain Language Summary: Fluid mud is an intermediate stage between a consolidated seafloor and dilute fine sediment suspension. Its high density (>10 g/L) and downslope movement are important in sediment transport over the inner continental shelf (water depths < 15 m). In this study we adopted a numerical model to simulate fluid mud transport on the Atchafalaya continental shelf in coastal Louisiana. We found that fluid mud formed during the passages of cold fronts, and its transport contributed to offshore sediment deposition. This downslope sediment transport process was more affected by the settling velocity of sediment particles rather than fluvial supply from the Atchafalaya River or sediment consolidation on the seabed. Key Points: Model results well reproduce hydrodynamics and WSFM dynamics during cold frontsWSFM transport results in onshore erosion and offshore deposition over the Atchafalaya inner shelfBed consolidation might influence WSFM concentration after several rounds of erosion [ABSTRACT FROM AUTHOR]

The seabed and the water column are tightly coupled in shallow coastal environments. Numerical models of seabed‐water interaction provide an alternative to observational studies that require concurrent measurements in both compartments, which are hard to obtain and rarely available. Here, we present a coupled model that includes water column biogeochemistry, seabed diagenesis, sediment transport and hydrodynamics. Our model includes realistic representations of biogeochemical reactions in both seabed and water column, and fluxes at their interface. The model was built on algorithms for seabed‐water exchange in the Regional Ocean Modeling System and expanded to include carbonate chemistry in seabed. The updated model was tested for two sites where benthic flux and porewater concentration measurements were available in the northern Gulf of Mexico hypoxic zone. The calibrated model reproduced the porewater concentration‐depth profiles and benthic fluxes of O2, dissolved inorganic carbon (DIC), TAlk, NO3 and NH4. We used the calibrated model to explore the role of benthic fluxes in acidifying bottom water during fair weather and resuspension periods. Under fair weather conditions, model results indicated that bio‐diffusion in sediment, labile material input and sediment porosity have a large control on the importance of benthic flux to bottom water acidification. During resuspension, the model indicated that bottom water acidification would be enhanced due to the sharp increase of the DIC/TAlk ratio of benthic fluxes. To conclude, our model reproduced the seabed‐water column exchange of biologically important solutes and can be used for quantifying the role of benthic fluxes in driving bottom water acidification over continental shelves. Plain Language Summary: In coastal environments where water is shallow, significant interactions occur between the seabed and the overlying water column. In the Northern Gulf of Mexico (NGoM) hypoxic zone, the seabed is believed to play an important role in the acidification of bottom ocean water. In this study we use a numerical model to understand how the seabed can affect bottom water acidification over the NGoM hypoxic zone. We found that during fair weather periods, mixing in the sediment bed due to biological activity, organic matter supply from the water column to the sediment, and the porosity of sediment itself can largely affect the role of the seabed in acidifying the bottom water. When the ocean condition is highly dynamic and resuspension occurs, the contribution of the seabed to bottom water acidification will likely be enhanced. Key Points: A coupled water column biogeochemical‐seabed diagenetic model is updated to include dissolved inorganic carbon (DIC) and TAlk for ocean acidificationThe modeled impact of benthic fluxes on bottom water acidification during quiescent periods is impacted by the intensity of bio‐diffusionResuspension enhances bottom water acidification by increasing the benthic flux DIC/TAlk ratio [ABSTRACT FROM AUTHOR]

Objective: The Atlantic Tripletail Lobotes surinamensis is a globally distributed subtropical and tropical fish species that inhabits estuaries throughout the northern Gulf of Mexico (GOM), particularly during warm months. Little is known about distribution and residency patterns within estuaries, as the species is rarely caught in the recreational fishery, and virtually no commercial fishery exists for the species in the GOM. Methods: We used data from a long‐term fishery‐independent gill‐net survey to model estuarine distribution throughout Texas and to relate environmental variables to the Atlantic Tripletail catch. Result: Although there were no observable temporal trends in catch over the time series (1990–2022), the most recent 6 years included record catch in six of the 10 major Texas estuaries, possibly indicating a recent pulse in abundance. Catch throughout the time series was spatially aggregated in a small number of "hot spots" observed coastwide. Latitude was the best predictor of catch, although wind fetch and wind aspect (wind direction in relation to shoreline direction) were important predictors, and catch was highest near GOM inlets. The Texas Parks and Wildlife Department gill‐net sampling program caught a range of Atlantic Tripletail between 171 and 880 mm total length, indicating a potential gear bias against juveniles. Conclusion: Despite this gear bias, these data shed light on the factors that drive Atlantic Tripletail estuarine distribution and abundance in the northwestern GOM. Wind‐driven passive movements in the estuary, combined with active selection of polyhaline habitats near GOM inlets, might be primary drivers of Atlantic Tripletail catch, thus supporting findings from previous studies. Impact statementAtlantic Tripletail are a popular recreational fishing species throughout the Gulf of Mexico. In Texas estuaries, Atlantic Tripletail are clustered in hot spots, which are typified by windward shorelines, and present mainly during the high‐use fishing season. They are rarely observed at water temperatures below 20°C. [ABSTRACT FROM AUTHOR]

The ecological impacts of multiple stressors are hard to predict but important to understand. When multiple stressors influence foundation species, the effects can cascade throughout the ecosystem. Gulf of Mexico seagrass ecosystems are currently experiencing a suite of novel stressors, including warmer water temperatures and increased herbivory due to tropicalization and conservation efforts. We investigated the impact of warming temperatures and grazing history on plant performance, morphology, and palatability by integrating a mesocosm study using the seagrass Thalassia testudinum with feeding trials using the sea urchin Lytechinus variegatus. Warming temperatures negatively impacted T. testudinum tolerance traits, reducing belowground biomass by 34%, productivity by 74%, shoot density by 10%, and number of leaves per plant by 24%, and negatively impacted resistance traits through 13% lower toughness of young leaves and a trend for reduced leaf carbon:nitrogen. Lytechinus variegatus individuals preferred to consume plants grown under heated conditions, which supports findings of enhanced palatability. Simulated turtle grazing impacted more plant traits than grazing by other herbivores, potentially diminishing plant resilience to future disturbances through reduced rhizome non‐structural carbohydrate concentrations and increasing palatability through reduced fiber content and 23% lower leaf carbon:phosphorus. Simulated turtle, simulated parrotfish, and urchin grazing reduced leaf carbon:nitrogen by 11%, also potentially increasing nutritive value. Interactions between warming temperatures and grazers on plant traits were additive for 16 out of 19 response variables. However, the stressors non‐additively impacted the number of leaves per plant, fiber content, and epiphyte load. We suggest that the impacts of grazers on leaf turnover rate and leaf age may vary based on water temperature, potentially driving these interactions. Overall, increased temperatures and grazing pressure will likely reduce seagrass resilience, structure, and biomass, potentially impacting feedback systems and producing negative consequences for seagrass cover, associated species, and ecosystem services. [ABSTRACT FROM AUTHOR]

Multi‐sensor data collected with in situ and satellite instruments during August 2015 were used to understand how the three‐dimensional bio‐optical properties of a Loop Current Eddy (LCE) in the Gulf of Mexico (GoM) contrast those of the background waters, and how these properties are related to physical and chemical properties. With a surface radius of ∼150 km and vertical extension to 1,400–1,500 m, the LCE was found to have highly stratified waters in two layers, with one lying just below the mixed layer (16 m) and the other coinciding with the pycnocline (∼120–200 m within the eddy). Strong contrasts were found in the bio‐optical properties (chlorophyll‐a concentration, absorption of particulate and dissolved matters, particulate backscattering, and beam‐c attenuation) across the eddy core, eddy edge, and surrounding waters. Absorption coefficients (400 nm) of surface particulate and dissolved matters were ∼4 times higher in the surrounding waters than in the eddy core, while surface reflectance (400 nm) in the eddy core was ∼7 times higher than in the surrounding waters. The magnitude of deep chlorophyll maximum (DCM) was comparable (0.3–0.33 mg/m3) in all waters, but the depth of DCM in the eddy core (∼115 m) was much deeper than in the surrounding waters (60–75 m). These contrasts were found to correspond to different water masses with different physical (temperature, density, and buoyancy frequency) and chemical properties (salinity and dissolved oxygen concentration), where physical processes (river plume advection and eddy‐induced downwelling) appeared to drive the changes in bio‐optical properties. Plain Language Summary: Loop Current Eddies (LCEs) are dominant circulation features in the Gulf of Mexico (GoM), which sporadically shed from the Loop Current (LC) with westward propagations. LCEs can transport heat, salt, dissolved oxygen, and other particulate and dissolved matters both horizontally and vertically. LCEs have been studied extensively, including their formations, shedding variability and prediction, moving paths, and interactions with topography. However, little is known about their bio‐optical properties, especially in the context of their physical and chemical contrasts from the background waters. Here, using multiple observational data sets collected during August 2015, we characterize the three‐dimensional bio‐optical, physical, and chemical properties of a LCE. With a mean radius of ∼150 km at the sea surface, the influence of the LCE extended to 1,400–1,500 m depth. The LCE was also found to have different bio‐optical, physical, and chemical properties from the surrounding waters at both surface and depth, where physical processes appeared to drive the different water masses that led to the observed changes. Key Points: The 3‐D bio‐optical, physical, and chemical properties of a Loop Current Eddy (LCE) were systemically characterized with observational data setsDifferences in bio‐optical and chemical properties of the eddy core, eddy edge, and surrounding waters were controlled by physical processesThe influence of the LCE extended to depths of 1,400–1,500 m [ABSTRACT FROM AUTHOR]

North African dust is known to be deposited in the Gulf of Mexico, but its deposition rate and associated supply of lithogenic dissolved metals, such as the abiotic metal thorium or the micronutrient metal iron, have not been well‐quantified. 232Th is an isotope with similar sources as iron and its input can be quantified using radiogenic 230Th. By comparing dissolved 232Th fluxes at three sites in the northern Gulf of Mexico with upwind sites in the North Atlantic, we place an upper bound on North African dust contributions to 232Th and Fe in the Gulf of Mexico, which is about 30% of the total input. Precision on this bound is hindered by uncertainty in the relative rates of dust deposition in the North Atlantic and the northern Gulf of Mexico. Based on available radium data, shelf sources, including rivers, submarine groundwater discharge, and benthic sedimentary releases are likely as important if not more important than dust in the budget of lithogenic metals in the Gulf of Mexico. In other words, it is likely there is no one dominant source of Th and Fe in the Gulf of Mexico. Finally, our estimated Fe input in the northern Gulf of Mexico implies an Fe residence time of less than 6 months, similar to that in the North Atlantic despite significantly higher supply rates in the Gulf of Mexico. Plain Language Summary: The ocean's nutrients generally come from land. The specific route a nutrient takes depends on the nutrient. For the nutrient iron, the rain of airborne dust blown from deserts is thought to be a significant source, especially in the remote ocean. This is because iron is very insoluble and usually cannot travel far in the water. The Gulf of Mexico is a semi‐enclosed sea with significant contact with ocean margin sediments and rivers. It is uncertain how this margin source might compare to airborne dust in the Gulf of Mexico. In this study, we used another element, thorium, to trace these two sources and found that dust is likely a significant but not dominant source. Key Points: An upper bound on the contribution of North African dust toward dissolved thorium supply in the northern Gulf of Mexico may be around 30%Thorium and other tracers suggest significant additional sources from the Gulf of Mexico shelf as well as slope and abyssal sedimentsThorium‐based lithogenic supply of iron suggests dissolved iron residence time in the northern Gulf of Mexico is less than 6 months [ABSTRACT FROM AUTHOR]

Estuaries exist across a large climatic gradient in the northwestern Gulf of Mexico, capturing a range of hydrologic conditions and estuarine functioning. We examined freshwater inflow, salinity, and stable isotope compositions (δ13C, δ15N) of oysters, suspended particulate organic matter (SPOM), and surface sediment organic matter (SSOM) from five estuaries across the hydrologic gradient. All five estuaries experienced large decreases in freshwater inflow over the last 40 yr, with three estuaries being subject to freshwater inflow reductions of more than 85%. Generally, these freshwater inflow decreases were associated with estuarine salinity increases. Across the spatial gradient, average salinity generally increased from northeast to southwest estuaries. SPOM in the northeastern, lower salinity estuaries generally contained more continental organic matter and was of higher quality (i.e., lower C/chlorophyll a ratio), as compared to southwestern, higher salinity estuaries. Similarly, both SSOM and oyster δ13C values were positively correlated with salinity, further highlighting that food webs in lower salinity estuaries are more greatly influenced by continental organic matter than those in higher salinity estuaries. A decrease in the connectivity between continental and coastal habitats may have broad consequences for flows of organic matter, and estuarine function and health. Conducting studies across large‐scale hydrologic gradients can provide a useful approach to informing and predicting shifts in estuarine functioning. [ABSTRACT FROM AUTHOR]

Wave-seabed interaction is known to be a fundamental cause of sediment instability and entrainment. Observations of burial for surrogate munitions were made with a high frequency, sector scanning sonar acquiring acoustic images of the seabed every 12 min during a storm event in May 2013 in the northern Gulf of Mexico offshore of Panama City Beach, FL. Surrogate munitions burial depth was verified by divers. Driven by time series of pressure observed near the seabed, an existing poro-elastic wave-sediment interaction model in combination with a sediment failure criterion due to liquefaction (loss of vertical effective stress) was used to correctly estimate depth and timing of burial. We introduce the concept of liquefaction degree, which is defined as the portion of vertical effective stress at the sediment surface that is, counteracted by wave-induced pore pressures. The relationship between wave-induced pressure at the seabed and liquefaction degree is expressed by a complex transfer function, indicating the importance of the swell band with respect to infra-gravity and short-wave components. The liquefaction degree was used to construct and calibrate a dynamical relationship between wave action and acoustic backscatter observations near the seabed, taken as a surrogate for suspended sediment concentration. Predictions of backscatter based on liquefaction degree were accurate at time scales of 15 s-30 min during most of the time span analyzed and superior to predictions of backscatter based on shear stress. The observations and analysis provide evidence for the importance of wave-induced seepage forces in describing sediment liquefaction and entrainment processes. [ABSTRACT FROM AUTHOR]

International efforts to restore degraded ecosystems will continue to expand over the coming decades, yet the factors contributing to the effectiveness of long‐term restoration across large areas remain largely unexplored. At large scales, outcomes are more complex and synergistic than the additive impacts of individual restoration projects. Here, we propose a cumulative‐effects conceptual framework to inform restoration design and implementation and to comprehensively measure ecological outcomes. To evaluate and illustrate this approach, we reviewed long‐term restoration in several large coastal and riverine areas across the US: the greater Florida Everglades; Gulf of Mexico coast; lower Columbia River and estuary; Puget Sound; San Francisco Bay and Sacramento–San Joaquin Delta; Missouri River; and northeastern coastal states. Evidence supported eight modes of cumulative effects of interacting restoration projects, which improved outcomes for species and ecosystems at landscape and regional scales. We conclude that cumulative effects, usually measured for ecosystem degradation, are also measurable for ecosystem restoration. The consideration of evidence‐based cumulative effects will help managers of large‐scale restoration capitalize on positive feedback and reduce countervailing effects. [ABSTRACT FROM AUTHOR]

Increasing green turtle abundance will lead to increased grazing within seagrass habitats—ecosystems that are important for carbon sequestration and storage. However, it is not well understood how carbon dynamics in these ecosystems respond to grazing and whether a response differs among meadows or locations.We measured seagrass ecosystem metabolism in grazed and ungrazed areas of Thalassia testudinum meadows with established green turtle foraging areas across the Greater Caribbean and Gulf of Mexico. We sampled meadows from five locations that differed in seagrass and environmental characteristics. Established meadows of the invasive seagrass Halophila stipulacea were also present at two of these locations, and we measured ecosystem metabolism in these meadows for comparison to grazed and ungrazed areas of the native T. testudinum.Across all individual sites, rates of net ecosystem production (NEP) ranged from 56% to 96% lower in grazed areas than ungrazed areas of T. testudinum meadows. Rates of NEP were also strongly, positively correlated with above‐ground seagrass biomass across sites. While metabolic carbon capture rates were lower in grazed areas, heterotrophic respiration was not stimulated, and grazing therefore did not result in significant metabolic remineralization of carbon in these meadows. NEP in H. stipulacea meadows was similar to rates in T. testudinum meadows at all three sites, suggesting that metabolic carbon capture may remain similar in Caribbean meadows where this invasive seagrass is replacing native species.Synthesis. Our results show that there is a consistent response in metabolic carbon dynamics to green turtle grazing in T. testudinum meadows across the Greater Caribbean region. An increase in grazing will not likely stimulate remineralization of carbon as these important habitats are returned to a natural grazed state. [ABSTRACT FROM AUTHOR]

To fully assess the long‐term impacts of oil spills like the 2010 Deepwater Horizon incident in the northern Gulf of Mexico, the potential for organisms other than microbes to affect the fate and distribution of the oil may have to be considered. This influence could be substantial for abundant bioturbating benthic animals like the ghost shrimp Lepidophthalmus louisianensis. An assessment of the influence of these ghost shrimp on petroleum hydrocarbons was conducted in laboratory micro‐ and mesocosms containing coastal Gulf of Mexico sediment, seawater, and oil or the polynuclear aromatic hydrocarbon (PAH) pyrene. In an experiment with pyrene added to the water column, the ghost shrimp presence lowered water‐column pyrene concentrations. In an experiment with oil added to the sediment surface, the ghost shrimp presence decreased PAH concentrations in the sediment surface layer but increased these in the water column and subsurface sediment. A companion study and a mass‐balance analysis indicated a net loss of PAHs through an enhancement of microbial degradation. In an experiment in which oil was added as a narrow subsurface layer in the sediment, the ghost shrimp presence appeared to broaden the oil's depth distribution. Taken together, these results demonstrate that ghost shrimp can significantly influence the biodegradation and distribution of spilled oil in coastal ecosystems. Environ Toxicol Chem 2020;39:637–647. © 2019 SETAC [ABSTRACT FROM AUTHOR]

To better understand lateral dispersion of buoyant and nonbuoyant pollutants within the surface waters of large lakes, two lateral dispersion experiments were carried out in Lake Michigan during the stratified period: (1) a dye tracking experiment lasting 1 d; and (2) a drifter tracking experiment lasting 24 d. Both the dye patch and drifters were surface‐released at the center of Lake Michigan's southern basin. Near‐surface shear induced by near‐inertial Poincaré waves partially explains elevated dye dispersion rates (1.5–4.2 m2 s−1). During the largely windless first 5 d of the drifter release, the drifters exhibited nearly scale‐independent dispersion (K ∼ L0.2), with an average dispersion coefficient of 0.14 m2 s−1. Scale‐dependent drifter dispersion ensued after 5 d, with K ∼ L1.09 and corresponding dispersion coefficients of 0.3–2.0 m2 s−1 for length scales L = 1500–8000 m. The largest drifter dispersion rates were found to be associated with lateral shear‐induced spreading along a thermal front. Comparisons with other systems show a wide range of spreading rates for large lakes, and larger rates in both the ocean and the Gulf of Mexico, which may be caused by the relative absence of submesoscale processes in offshore Lake Michigan. [ABSTRACT FROM AUTHOR]

Prior to the Deepwater Horizon oil spill, we lacked a comprehensive baseline of oil contamination in the Gulf of Mexico's sediments, water column, and biota. Gaps in prespill knowledge limit our ability to determine the aftereffects of the Deepwater Horizon blowout or prepare to mitigate similar impacts during future oil spill disasters. We examined spatiotemporal differences in exposure to and metabolism of polycyclic aromatic hydrocarbons (PAHs) in 2 hake species (Urophycis spp.) to establish a current baseline for these ecologically important, abundant, and at‐risk demersal fishes. Gulf hake (Urophycis cirrata) and southern hake (Urophycis floridana) were collected throughout the Gulf of Mexico during extensive longline surveys from 2012 to 2015. Analyses of biliary PAH metabolites and liver PAH concentrations provided evidence of exposures to di‐ and tricyclic compounds, with the highest concentrations measured in the northern Gulf of Mexico. Species‐specific differences were not detected, but temporal trends observed in biliary PAHs suggest a decrease in acute exposures, whereas increasing liver PAHs suggest chronic exposures marked by greater assimilation than metabolism rates. To our knowledge, the present study provides the first multitissue contaminant analyses, as well as the most exhaustive biometric analyses, for both gulf and southern hakes. Though sources of exposure are complex because of multiple natural and anthropogenic PAH inputs, these results will facilitate the development of much needed health metrics for Gulf of Mexico benthos. Environ Toxicol Chem 2019;38:2740–2749. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

A time series of polycyclic aromatic hydrocarbon (PAH) data was collected for Gulf of Mexico demersal fishes in the years following the Deepwater Horizon oil spill (2012–2017). Tilefish (Lopholatilus chamaeleonticeps) were sampled via demersal longline at repeat stations in the northern Gulf of Mexico in 2012 to 2015 and 2017. Bile samples (n = 256) were analyzed via high‐performance liquid chromatography with fluorescence detection for PAH metabolites as a biomarker of exposure to PAHs. Liver tissues (n = 230) were analyzed for accumulation of PAHs and alkylated homologs via quick, easy, cheap, effective, rugged, and safe (QuEChERS) extractions and gas chromatography–tandem mass spectrometry quantification. Over the 6‐yr time series, exposure to petrogenic PAHs increased by an average of 178%, correlating with an average 22% decline in Fulton's condition factor. The decline in Fulton's condition factor was positively correlated with a 53% decline in percentage of liver lipid. There was no accumulation of PAHs in liver tissue over time. Together, these results suggest that increasing and chronic PAH exposure and metabolism may be taxing the energy budgets of tilefish, particularly adult females, with potentially negative impacts on fitness. Environ Toxicol Chem 2019;38:2659–2671. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Acetate is a key intermediate of organic matter mineralization, but its metabolism remains largely unconstrained in the pelagic ocean. We conducted an integrated biogeochemical study to investigate microbial acetate cycling in the northern Gulf of Mexico with the goal of elucidating the importance of acetate as a carbon and energy source. Acetate was used primarily as an energy source, as evidenced by observed oxidation rates (rate constant k: 0.06–0.22 day−1) that varied between 42% and 96% of total biological acetate uptake (i.e., assimilation + oxidation; k: 0.06–0.34 day−1). The assimilation of acetate into biomass (k: 0.01–0.20 day−1) illustrated the potential significance of acetate as a biomass carbon source, particularly in nutrient‐rich coastal waters. No relationship between acetate assimilation or oxidation and environmental factors, such as chlorophyll and nutrients, was observed. However, elevated acetate uptake in reduced oxygen waters characterized by particulate organic carbon mineralization suggests that acetate metabolism may be a good proxy for particulate organic carbon breakdown. Molecular genetic analysis revealed that SAR11 Alphaproteobacteria were the most abundant heterotrophic bacteria and suggest that they may utilize acetate. At some sites, acetate carbon may have accounted for up to 50.4% of the bacterial carbon production. These results suggest that acetate may serve as an important carbon and energy source for heterotrophic bacteria thus revealing a potentially significant role of acetate for dissolved organic carbon cycling in the ocean. Key Points: Acetate was used primarily as an energy source but was also an important structural carbon source, especially in coastal watersAcetate metabolism was not correlated with chlorophyll or nutrients but tracked POC degradation and O2 consumption in the water columnThe carbon incorporated into biomass from acetate may support a substantial fraction of bacterial production [ABSTRACT FROM AUTHOR]

Sargassum is one of the most species-rich genera in the brown algae with over 400 described species worldwide. The bulk of these species occurs in Pacific-Indian ocean waters with only a small portion found on the Atlantic side of the Isthmus of Panama. Sargassum also has one of the most subdivided and complex taxonomic systems used within the algae. Systematic distinctions within the genus are further complicated by high rates of phenotypic variability in several key morphological characters. Molecular analyses in such systems should allow testing of systematic concepts while providing insights into speciation and evolutionary patterns. Global molecular phylogenetic analyses using both conserved and variable regions of the Rubisco operon ( rbcL and rbcL-IGS-rbcS) were performed with species from the Gulf of Mexico, Caribbean, and Pacific basin. Results confirm earlier analyses based on rbcL-IGS- rbcS from Pacific species at the subgeneric and sectional level while providing additional insights into the systematics and phylogenetics on a global scale. For example, species east of the Isthmus of Panama form a distinct well-resolved clade within the tropical subgenus. This result in sharp contrast to traditional systematic treatments but provides a window into the evolutionary history of this genus in the Pacific and Atlantic Ocean basins and a possible means to time speciation events. [ABSTRACT FROM AUTHOR]

The algal communities of the Flower Garden Banks National Marine Sanctuary have not been comprehensively evaluated and only a few dominant macroalgal species have been reported. This study utilizes both destructive and non-destructive sampling techniques to characterize and taxonomically identify the ‘algal mat’ community structure. The East and West Flower Garden Banks are located on the outer continental shelf approximately 200 km off the Texas-Louisiana coastline. The average depth of both banks is 100 m with the crest approximately 20 m from the surface. Harvest and photogrammetric samples were collected during two extended cruises to the Flower Garden Banks in October 1998 and March 1999. Forty, 0.25-m2 quadrats of standing stock material were randomly collected along with one hundred sixty-one 0.25 m2 photo-quadrats from an average depth of 27 m. Photo-transparencies were projected to an actual size grid with 25 random points. Four thousand twenty-five transparency points were evaluated and used to calculate percent composition of algal cover. Harvest samples were used to characterize the “algal mat” composition, species richness, abundance, and biomass. Forty-two species were identified from the samples representing 14 Orders. The “red algal mat” was the dominant algal coverage comprising 38.4% of all photogrammetric samples. This mat was primarily composed of members from the Order Ceramiales. Centroceras, Ceramium, and Polysiphonia comprised 33.4% of the mat, Anotrichium and Hypoglossum, 22.4%. [ABSTRACT FROM AUTHOR]

The upper northwestern Gulf basin is characterized by a relatively shallow but well-developed continental shelf with an extensive system of mid- and outer shelf hard banks of varying origin and composition. Observations done by our laboratory while participating in monitoring cruises to the National Marine Sanctuaries of the East and West Banks of the Texas Flower Gardens, Stetson Banks (TX) and Sonnier Banks (LA) reveal a surprisingly different floristic composition among the sites. Several range extensions, new macro-algal records for the Gulf of Mexico, and new species imply a much more complex Algal Zone community than the one proposed by Rezak et al. (1985). Our ongoing project includes the development of a modern taxonomic, phylogenetic, morphological and genetic database essential to informed management for preservation of biological diversity. It also provides a framework of seasonal algal composition against which long-term trends and anomalies in algal distribution and health of the Gulf of Mexico can be assessed at future dates. [ABSTRACT FROM AUTHOR]

Generic and species concepts within the red algal assemblages Halymeniales and Rhodymeniales are discussed for taxa inhabiting the western Gulf of Mexico. Two principal biogeographic assemblages occur: an off-shore deep-water group (including Coelarthrum cliftonii, Halymenia spp., Botryocladia spp., Gloiocladia) representing remnants of a Tethyan distribution, and a near-shore intertidal flora (comprising Rhodymenia, Grateloupia and Prionitis) which instead reveals biogeographic affinities with the Carolinian Province. These two distinct marine floras will be contrasted phylogenetically based on DNA sequence analysis inferred from chloroplast-encoded rbcL. The generic descriptions of Grateloupia and Prionitis are in need of taxonomic revision based on a survey of species from Caribbean and Pacific Mexico. [ABSTRACT FROM AUTHOR]

Despite a recent body of literature, the species of Gracilaria recognized for the Gulf of Mexico are still incompletely characterized, misidentified, and species limits not well defined due to huge morphological plasticity and overlapping habits. To better characterize these taxa and evaluate their taxonomic relationships, we provide a chloroplast-encoded rbcL phylogeny encompassing primarily Gulf, western Atlantic, and Caribbean species. Our results indicate the need to resurrect older, validly published names currently placed in synonymy under other species of Gracilaria, and to describe new species. For Gracilaria tikvahia, in particular, a combination of DNA sequences [ rbcL, and internal transcribed spacer regions (ITS) of nuclear ribosomal DNA] from specimens collected across a wide biogeographic area (Nova Scotia, Canada, to Las Coloradas, Yucatan Peninsula) successfully promotes the integration and correlation of molecular phylogenies and morphology with biogeographic hypotheses. [ABSTRACT FROM AUTHOR]