Gulf Coast Beaches Research Articles

Enrichment of Lipophilic Brevetoxins in Sea Spray Aerosol during Red-Tides

Red tide is caused by the accumulation of Karenia (K.) brevis, which produces brevetoxin (BTx), a neurotoxin. Excreted BTx is incorporated into sea spray aerosol (SSA), which is created from the bursting of bubbles at the ocean’s surface. For the first time, this study measures the enrichment factor of BTx in K. brevis algal aerosol. During red-tide events in 2021 and 2022, aerosol and water samples were collected from Gulf Coast beaches in Southwest Florida with various levels of K. brevis growth. The concentrations of BTx in SSA were measured using an enzyme-linked immunosorbent assay kit. The concentrations of both aerosolized BTx and organic matter (OM) were normalized using that of sodium ions and were shown to be significantly higher than those observed in seawater. Lipophilic BTx is present in SSA at concentrations that are 2-4 orders of magnitude higher than seawater, and 1-2 orders of magnitude higher than concentrations of OM in SSA. Enrichment of aerosolized BTx was also simulated in the algal culture tank with two different aerosol generation methods. The estimated activity coefficient (order of 1019) of BTx in bulk seawater using the inorganic thermodynamic model indicates very poor solubility of BTx in seawater and supports its enrichment in ocean surfaces and SSA. Examining the enrichment factors of BTx and organic matter in SSA contributes to our comprehension of the potential respiratory challenges posed by inhaled algal aerosols during red tide occurrences. In addition, enriched BTx in the uppermost layer of the ocean during red tide blooms can adversely influence animals that inhabit in tide flats with neurological and respiratory impacts.

An enhancer of Agouti contributes to parallel evolution of cryptically colored beach mice

Identifying the genetic basis of repeatedly evolved traits provides a way to reconstruct their evolutionary history and ultimately investigate the predictability of evolution. Here, we focus on the oldfield mouse (Peromyscus polionotus), which occurs in the southeastern United States, where it exhibits considerable color variation. Dorsal coats range from dark brown in mainland mice to near white in mice inhabiting sandy beaches; this light pelage has evolved independently on Florida's Gulf and Atlantic coasts as camouflage from predators. To facilitate genomic analyses, we first generated a chromosome-level genome assembly of Peromyscus polionotus subgriseus. Next, in a uniquely variable mainland population (Peromyscus polionotus albifrons), we scored 23 pigment traits and performed targeted resequencing in 168 mice. We find that pigment variation is strongly associated with an ∼2-kb region ∼5 kb upstream of the Agouti signaling protein coding region. Using a reporter-gene assay, we demonstrate that this regulatory region contains an enhancer that drives expression in the dermis of mouse embryos during the establishment of pigment prepatterns. Moreover, extended tracts of homozygosity in this Agouti region indicate that the light allele experienced recent and strong positive selection. Notably, this same light allele appears fixed in both Gulf and Atlantic coast beach mice, despite these populations being separated by >1,000 km. Together, our results suggest that this identified Agouti enhancer allele has been maintained in mainland populations as standing genetic variation and from there, has spread to and been selected in two independent beach mouse lineages, thereby facilitating their rapid and parallel evolution.

How Does Congestion Affect the Evaluation of Recreational Gate Fees? An Application to Gulf Coast Beaches

We investigate how congestion influences the welfare, revenue-raising, and distributional implications of gate fees at outdoor recreational sites. A simple conceptual framework decomposes the effects of gate fees into three components, which are then quantified in an application to Gulf Coast beaches. Simulation results suggest that when congestion is a disamenity, the deadweight loss from gate fees declines, the revenue raised grows, and leakage to untaxed sites is less. Congestion feedbacks do not substantively change our distributional analysis, which implies that gate fees are regressive, do not disproportionately affect minorities, and privilege local recreators at the expense of overnight visitors.

Responses by Atlantic Ghost Crab (Ocypode quadrata) Populations to Hurricane Impacts on a Texas Beach: A 10-Year Study

The Atlantic ghost crab (Ocypode quadrata) is a widely distributed predator and scavenger along Atlantic Ocean and Gulf Coast beaches. A long-term study was initiated on the Bolivar Peninsula of Texas in 2006 to assess the impact of human activity on ghost crabs. Line transects were used to determine crab burrow arrangement at a high-impact site and a low-impact site. Differences were found between the two sites in number of active burrows per transect, burrow density, the diameter of burrow openings, burrow distance to the high-water line, and nearest-neighbor distances. In Fall 2008, Hurricane Ike struck the study sites. Re-examinations of the sites in 2010 showed changes in ghost crab burrows. The high-impact site experienced a decline in human activity – beach width increased by > 50%, the number of burrows/transect tripled, and nearest-neighbor distances decreased by one-third. The hurricane also reshaped the low-impact site on the western tip of the peninsula as beach width decreased by two-thirds, burrow density increased by sevenfold, and nearest-neighbor distances decreased by one-half. Sampling in 2012, 2014, and 2016 show that some of the physical characteristics of the beach gradually returned to near pre-hurricane status. However, reduced beach space at the low-traffic site remained, with higher burrow density and reduced crab size persisting 8 years after the hurricane, and the post-storm reduction in human traffic in the high-impact site has maintained higher burrow density there even as traffic increased. Monitoring the ecological impact of hurricanes is of growing importance as global climate change could lead to increased frequency and severity of tropical storms.

Hurricane Isaac brings more than oil ashore: Characteristics of beach deposits following the Deepwater Horizon spill.

Prior to Hurricane Isaac making landfall along the Gulf of Mexico coast in August 2012, local and state officials were concerned that the hurricane would mobilize submerged oiled-materials from the Deepwater Horizon (DWH) spill. In this study, we investigated materials washed ashore following the hurricane to determine if it affected the chemical composition or density of oil-containing sand patties regularly found on Gulf Coast beaches. While small changes in sand patty density were observed in samples collected before and after the hurricane, these variations appear to have been driven by differences in sampling location and not linked to the passing of Hurricane Isaac. Visual and chemical analysis of sand patties confirmed that the contents was consistent with oil from the Macondo well. Petroleum hydrocarbon signatures of samples collected before and after the hurricane showed no notable changes. In the days following Hurricane Isaac, dark-colored mats were also found on the beach in Fort Morgan, AL, and community reports speculated that these mats contained oil from the DWH spill. Chemical analysis of these mat samples identified n-alkanes but no other petroleum hydrocarbons. Bulk and δ13C organic carbon analyses indicated mat samples were comprised of marshland peat and not related to the DWH spill. This research indicates that Hurricane Isaac did not result in a notable change the composition of oil delivered to beaches at the investigated field sites. This study underscores the need for improved communications with interested stakeholders regarding how to differentiate oiled from non-oiled materials. This is especially important given the high cost of removing oiled debris and the increasing likelihood of false positives as oiled-materials washing ashore from a spill become less abundant over time.

Evaluation of behavioral parameters, hematological markers, liver and kidney functions in rodents exposed to Deepwater Horizon crude oil and Corexit

The 2010 Deepwater Horizon (DWH) oil spill is the largest marine oil spill in US history. In the aftermath of the spill, the response efforts used a chemical dispersant, Corexit, to disperse the oil spill. The health impacts of crude oil and Corexit mixture to humans, mammals, fishes, and birds are mostly unknown. The purpose of this study is to investigate the in vivo effects of DWH oil, Corexit, and oil-Corexit mixture on the general behavior, hematological markers, and liver and kidney functions of rodents. C57 Bl6 mice were treated with DWH oil (80 mg/kg) and/or Corexit (95 mg/kg), and several hematological markers, lipid profile, liver and kidney functions were monitored. The results show that both DWH oil and Corexit altered the white blood cells and platelet counts. Moreover, they also impacted the lipid profile and induced toxic effects on the liver and kidney functions. The impacts were more pronounced when the mice were treated with a mixture of DWH-oil and Corexit. This study provides preliminary data to elucidate the potential toxicological effects of DWH oil, Corexit, and their mixtures on mammalian health. Residues from the DWH spill continue to remain trapped along various Gulf Coast beaches and therefore further studies are needed to fully understand their long-term impacts on coastal ecosystems.

Modeling Fecal Coliform Bacteria Levels at Gulf Coast Beaches

This study presents and compares two models for predicting fecal coliform levels at Gulf Coast beaches in Louisiana, USA. One was developed using the artificial neural network (ANN) in MATLAB toolbox and the other one was developed based on the multiple linear regression method (MLR). A total of six independent environmental variables, including rainfall, tide, wind, salinity, temperature, and weather type along with eight different combinations of the independent variables are capable of explaining about 76 % of variation in fecal coliform levels for model training data and 44 % for independent data. The findings are obtained from the ANN model and the MLR model using six years of bacteriological and environmental monitoring data. The results show that the ANN model performs consistently better than the MLR model. Applications of the ANN model can significantly reduce potential health risks of fecal pollution to beachgoers. The paper provides new insights into environmental processes responsible for the variation in levels of fecal coliform bacteria in coastal beach waters as well.

Effects of Beach Renourishment and Clutch Relocation on the Success of the Loggerhead Sea Turtle (Caretta caretta) Eggs and Hatchlings

Along the coasts of Florida, beach erosion caused by large storms and hurricanes coincides with the nesting season of the Loggerhead Sea Turtle. Here, we report the effects of beach renourishment and nest relocation on the success of Loggerhead Sea Turtle (Caretta caretta) eggs and hatchlings. Data on ∼53,700 Loggerhead Sea Turtle eggs from 517 clutches were collected over a six-year period, 2006 through 2011, on the Gulf Coast beaches of Pinellas County, Florida. We compared the proportion of eggs that hatched and hatchlings that emerged based on relocation; the type of beach on which breeders deposited their eggs (natural or renourished), and the type of beach to which clutches were relocated (natural or renourished). In this study, beach renourishment had no adverse effect on the proportion of eggs that hatched or the proportion of hatchlings that emerged. In contrast, clutch relocation decreased the proportion of inundated clutches 10-fold from 28–3%; an important finding as water inundation destroyed nearly half of the eggs per clutch. These findings add to a growing body of research on beach renourishment and clutch relocation with important implications for the continued management of Loggerhead Sea Turtle nests.

The polycyclic aromatic hydrocarbon degradation potential of Gulf of Mexico native coastal microbial communities after the Deepwater Horizon oil spill.

The Deepwater Horizon (DWH) blowout resulted in oil transport, including polycyclic aromatic hydrocarbons (PAHs) to the Gulf of Mexico shoreline. The microbial communities of these shorelines are thought to be responsible for the intrinsic degradation of PAHs. To investigate the Gulf Coast beach microbial community response to hydrocarbon exposure, we examined the functional gene diversity, bacterial community composition, and PAH degradation capacity of a heavily oiled and non-oiled beach following the oil exposure. With a non-expression functional gene microarray targeting 539 gene families, we detected 28,748 coding sequences. Of these sequences, 10% were uniquely associated with the severely oil-contaminated beach and 6.0% with the non-oiled beach. There was little variation in the functional genes detected between the two beaches; however the relative abundance of functional genes involved in oil degradation pathways, including polycyclic aromatic hydrocarbons (PAHs), were greater in the oiled beach. The microbial PAH degradation potentials of both beaches, were tested in mesocosms. Mesocosms were constructed in glass columns using sands with native microbial communities, circulated with artificial sea water and challenged with a mixture of PAHs. The low-molecular weight PAHs, fluorene and naphthalene, showed rapid depletion in all mesocosms while the high-molecular weight benzo[α]pyrene was not degraded by either microbial community. Both the heavily oiled and the non-impacted coastal communities showed little variation in their biodegradation ability for low molecular weight PAHs. Massively-parallel sequencing of 16S rRNA genes from mesocosm DNA showed that known PAH degraders and genera frequently associated with oil hydrocarbon degradation represented a major portion of the bacterial community. The observed similar response by microbial communities from beaches with a different recent history of oil exposure suggests that Gulf Coast beach communities are primed for PAH degradation.

Correction: Shifts in the Microbial Community Composition of Gulf Coast Beaches Following Beach Oiling

Correction: Shifts in the Microbial Community Composition of Gulf Coast Beaches Following Beach Oiling

Shifts in the Microbial Community Composition of Gulf Coast Beaches Following Beach Oiling

Microorganisms associated with coastal sands serve as a natural biofilter, providing essential nutrient recycling in nearshore environments and acting to maintain coastal ecosystem health. Anthropogenic stressors often impact these ecosystems, but little is known about whether these disturbances can be identified through microbial community change. The blowout of the Macondo Prospect reservoir on April 20, 2010, which released oil hydrocarbons into the Gulf of Mexico, presented an opportunity to examine whether microbial community composition might provide a sensitive measure of ecosystem disturbance. Samples were collected on four occasions, beginning in mid-June, during initial beach oiling, until mid-November from surface sand and surf zone waters at seven beaches stretching from Bay St. Louis, MS to St. George Island, FL USA. Oil hydrocarbon measurements and NOAA shoreline assessments indicated little to no impact on the two most eastern beaches (controls). Sequence comparisons of bacterial ribosomal RNA gene hypervariable regions isolated from beach sands located to the east and west of Mobile Bay in Alabama demonstrated that regional drivers account for markedly different bacterial communities. Individual beaches had unique community signatures that persisted over time and exhibited spatial relationships, where community similarity decreased as horizontal distance between samples increased from one to hundreds of meters. In contrast, sequence analyses detected larger temporal and less spatial variation among the water samples. Superimposed upon these beach community distance and time relationships, was increased variability in bacterial community composition from oil hydrocarbon contaminated sands. The increased variability was observed among the core, resident, and transient community members, indicating the occurrence of community-wide impacts rather than solely an overprinting of oil hydrocarbon-degrading bacteria onto otherwise relatively stable sand population structures. Among sequences classified to genus, Alcanivorax , Alteromonas , Marinobacter , Winogradskyella , and Zeaxanthinibacter exhibited the largest relative abundance increases in oiled sands.

Environmental Factors Influencing the Abundance of Enterococci in Gulf Coast Beach Waters

AbstractEnterococci concentrations in seawater samples collected in 2010 at a Gulf Coast beach in the afternoon were significantly lower (12 MPN/100 mL) compared with morning samples (172 MPN/100 mL). The factors affecting temporal differences of enterococci concentration in beach waters were studied through five laboratory experiments analyzing beach sands, solar radiation, salinity, and turbidity. Enterococci were found in beach sands at a geometric mean of 43 MPN per 100 g of sand, demonstrated the ability to persist for extended periods of time, and increased when incubated (geometric mean of 54 MPN per 100 g sand). Solar radiation inactivated large enterococci concentrations (≥24,196 MPN/100 mL) in as little as four hours in salinities ranging from 0 to 25 parts per thousand (ppt). Increased turbidity (70 and 140 NTU) hindered the effect of solar radiation, suggesting that near-shore turbidity may promote higher enterococci concentrations. The results indicate that enterococci replenishment alo...

Development of predictive models for determining enterococci levels at Gulf Coast beaches

The US EPA BEACH Act requires beach managers to issue swimming advisories when water quality standards are exceeded. While a number of methods/models have been proposed to meet the BEACH Act requirement, no systematic comparisons of different methods against the same data series are available in terms of relative performance of existing methods. This study presents and compares three models for nowcasting and forecasting enterococci levels at Gulf Coast beaches in Louisiana, USA. One was developed using the artificial neural network (ANN) in MATLAB Toolbox and the other two were based on the US EPA Virtual Beach (VB) Program. A total of 944 sets of environmental and bacteriological data were utilized. The data were collected and analyzed weekly during the swimming season (May–October) at six sites of the Holly Beach by Louisiana Beach Monitoring Program in the six year period of May 2005–October 2010. The ANN model includes 15 readily available environmental variables such as salinity, water temperature, wind speed and direction, tide level and type, weather type, and various combinations of antecedent rainfalls. The ANN model was trained, validated, and tested using 308, 103, and 103 data sets (collected in 2007, 2008, and 2009) with an average linear correlation coefficient (LCC) of 0.857 and a Root Mean Square Error (RMSE) of 0.336. The two VB models, including a linear transformation-based model and a nonlinear transformation-based model, were constructed using the same data sets. The linear VB model with 6 input variables achieved an LCC of 0.230 and an RMSE of 1.302 while the nonlinear VB model with 5 input variables produced an LCC of 0.337 and an RMSE of 1.205. In order to assess the predictive performance of the ANN and VB models, hindcasting was conducted using a total of 430 sets of independent environmental and bacteriological data collected at six Holly Beach sites in 2005, 2006, and 2010. The hindcasting results show that the ANN model is capable of predicting enterococci levels at the Holly Beach sites with an adjusted RMSE of 0.803 and LCC of 0.320 while the adjusted RMSE and LCC values are 1.815 and 0.354 for the linear VB model and 1.961and 0.521 for the nonlinear VB model. The results indicate that the ANN model with 15 parameters performs better than the VB models with 6 or 5 parameters in terms of RMSE while VB models perform better than the ANN model in terms of LCC. The predictive models (especially the ANN and the nonlinear VB models) developed in this study in combination with readily available real-time environmental and weather forecast data can be utilized to nowcast and forecast beach water quality, greatly reducing the potential risk of contaminated beach waters to human health and improving beach management. While the models were developed specifically for the Holly Beach, Louisiana, the methods used in this paper are generally applicable to other coastal beaches.

Investigation of human sewage pollution and pathogen analysis at Florida Gulf coast Beaches

Water quality at two Florida beaches was compared using faecal indicator bacteria measurements, microbial source tracking (MST) methods for detecting human source pollution and the assessment of pathogen presence. These values were also compared before and after remediation of wastewater infrastructure at one beach. Faecal coliforms, Escherichia coli and enterococci were enumerated in estuarine water and sediment samples. PCR assays for the human-associated esp gene of Enterococcus faecium and human polyomaviruses (HPyVs) were used to detect human sewage. Culturable Salmonella and enteric viruses were also analysed. MST identified human sewage contamination at one beach, leading to repair of a sewer main and relocation of portable restrooms. Exceedances of Florida recreational water regulatory standards were significantly reduced after remediation (by 52% for faecal coliforms and 39% for enterococci), and the frequency of detection of MST markers decreased. Coxsackie virus B4 and HPyVs were codetected following a major sewage spill, but Salmonella was not detected during the study. These data indicate that infrastructure remediation significantly reduced pollution from human sewage at the impacted beach. A comprehensive microbial water quality study that can identify contamination sources through the use of MST markers and close collaboration with local/and state agencies can result in tangible actions to improve recreational water quality and safety.

Adaptive basis of geographic variation: genetic, phenotypic and environmental differences among beach mouse populations

A major goal in evolutionary biology is to understand how and why populations differentiate, both genetically and phenotypically, as they invade a novel habitat. A classical example of adaptation is the pale colour of beach mice, relative to their dark mainland ancestors, which colonized the isolated sandy dunes and barrier islands on Florida's Gulf Coast. However, much less is known about differentiation among the Gulf Coast beach mice, which comprise five subspecies linearly arrayed on Florida's shoreline. Here, we test the role of selection in maintaining variation among these beach mouse subspecies at multiple levels-phenotype, genotype and the environments they inhabit. While all beach subspecies have light pelage, they differ significantly in colour pattern. These subspecies are also genetically distinct: pair-wise F(st)-values range from 0.23 to 0.63 and levels of gene flow are low. However, we did not find a correlation between phenotypic and genetic distance. Instead, we find a significant association between the average 'lightness' of each subspecies and the brightness of the substrate it inhabits: the two most genetically divergent subspecies occupy the most similar habitats and have converged on phenotype, whereas the most genetically similar subspecies occupy the most different environments and have divergent phenotypes. Moreover, allelic variation at the pigmentation gene, Mc1r, is statistically correlated with these colour differences but not with variation at other genetic loci. Together, these results suggest that natural selection for camouflage-via changes in Mc1r allele frequency-contributes to pigment differentiation among beach mouse subspecies.

The Genetic Basis of Phenotypic Convergence in Beach Mice: Similar Pigment Patterns but Different Genes

Convergent evolution is a widespread phenomenon seen in diverse organisms inhabiting similar selective environments. However, it is unclear if similar phenotypes are produced by the same or different genes and mutations. Here we analyze the molecular mechanisms underlying convergent pigment pattern among subspecies of the beach mouse (Peromyscus polionotus) inhabiting the Gulf and Atlantic coasts of Florida. In these two geographic regions, separated by more than 300 km, "beach mice" have lighter colored coats than do their mainland counterparts, produced by natural selection for camouflage against the pale coastal sand dunes. We measured color pattern in eight beach mouse subspecies and showed that three of the Gulf Coast subspecies are more phenotypically similar to an Atlantic coast subspecies than to their Gulf Coast neighbors. However, light-colored beach mice do not form a monophyletic group. Previous results implicated a single derived amino acid change in the melanocortin-1 receptor (Mc1r) as a major contributor to pigment pattern in the Gulf Coast beach mice; despite phenotypic similarities, the derived Mc1r allele was not found in the Atlantic coast beach mouse populations. Here we show that Atlantic coast beach mice have high levels of Mc1r polymorphism but they lack unique alleles. Functional assays revealed that single amino acid mutations segregating in Atlantic coast beach mice do not cause any change in Mc1r activity compared with the activity of Mc1r from dark-colored mice. These joint results show that convergent pigment patterns in recently diverged beach mouse subspecies--whose developmental constraints are presumably similar--have evolved through a diversity of genetic mechanisms.

A Single Amino Acid Mutation Contributes to Adaptive Beach Mouse Color Pattern

Natural populations of beach mice exhibit a characteristic color pattern, relative to their mainland conspecifics, driven by natural selection for crypsis. We identified a derived, charge-changing amino acid mutation in the melanocortin-1 receptor (Mc1r) in beach mice, which decreases receptor function. In genetic crosses, allelic variation at Mc1r explains 9.8% to 36.4% of the variation in seven pigmentation traits determining color pattern. The derived Mc1r allele is present in Florida's Gulf Coast beach mice but not in Atlantic coast mice with similar light coloration, suggesting that different molecular mechanisms are responsible for convergent phenotypic evolution. Here, we link a single mutation in the coding region of a pigmentation gene to adaptive quantitative variation in the wild.

Fungal spores are transported long distances in smoke from biomass fires

Abstract Viable fungal spores are present in smoke from distant biomass fires. This finding has potentially important implications for prescribed burning, agricultural management and public health. While attempting to find fungal spores in dust blown from China to Texas, one of us (S.A.M.) discovered that smoke from Yucatan contains viable bacteria and fungal spores, including the genera Alternaria, Cladosporium, Fusariella and Curvularia. There was a high correlation (r2=0.78) of spores and coarse carbon particles collected on microscope slides during 13 days of the 2002 smoke season. To eliminate possible contamination by local spores, an air sampler was flown from a kite at a Texas Gulf Coast beach during and after the 2003 smoke season on days when the NOAA back trajectory showed air arriving from Yucatan. Fifty-two spores and 19 coarse black carbon particles (>2.5 μm) were collected during a 30-min kite flight on the smoke day and 12 spores and four carbons on the day without smoke. We have found spores in smoke from an Arizona forest fire and in Asian smoke at Mauna Loa Observatory, Hawaii. We have tested these findings by burning dried grass, leaves, twigs and flood detritus. The smoke from all test fires contained many spores.

Status and Habitat of Alabama Gulf Coast Beach Mice Peromyscus polionotus ammobates and P. p. trissyllepsis

The present study documents the distribution of the gulf coast beach mice (Peromyscus polionotus ammobates and P.p. trissyllepsis) in Alabama and assesses their status. Since 1921, approximately 62% of beach mouse habitat in Alabama has been lost. Populations of P. p. ammobates are concentrated on small tracts of habitat from the Fort Morgan peninsula to Romar Beach. P. p. trissyllepsis was found only at one site at Florida Point on Perdido Key. Live trapping for 1,566 trapnights yielded 157 beach mice. Area extrapolations were used to determine the density of P. p. ammobates. Approximately 875 P. p. ammobates were estimated to live on 134.6 ha (6.5 mice/ha). Only one P. p. trissyllepsis was trapped from 25.2 ha. The vegetation of the habitat is described. Factors responsible for the disappearance of beach mice in Alabama are discussed.

Carbonate Cementation of Gulf Coast Barrier-Island Sands and Formation of a Stratigraphic Trap: ABSTRACT

Field investigations in the area of Grand Isle, Louisiana, indicate the presence of active carbonate precipitation. Modern shoreline facies are being cemented by high-magnesium calcite, ranging from 10 to 50 mole % magnesium carbonate. Cementation occurs between the beach and marsh environments as surface crusts or laminae. The environment is characterized by seasonal high temperature (up to 50°C), high salinity (40 to 90^pmil), supratidal stromatolites and organic decomposition. After burial, lithified crusts undergo chemical alteration, as indicated by a decrease in magnesium carbonate content (20 to 35 mole %). The cement eventually undergoes dissolution and reprecipitation, forming a well-cemented sandstone. Rip-up clasts of these sandstones are found along Gulf Coast beaches where a transgressive sequence occurs. These clasts are typically cemented by high-magnesium calcite with 10 to 15 mole % magnesium carbonate. Carbon isotope analyses of rip-up clasts indicate that dissolution and reprecipitation processes are methane-derived due to organic decomposition. Buried crusts may be preserved in the subsurface and form an effective barrier to fluid migration. Where cementation is extensive, porosity is occluded on the marsh-side of the barrier-island sequence. Cement distribution is, therefore, a primary controlling agent of hydrocarbon migration and subsequent entrapment. Migration of hydrocarbons from organic-rich marsh sediments would be prevented by the early formation of the permeability barrier. Cementation, then, would account for accumulation of hydrocarbons on the marsh side of the barrier-island sequence and the formation of a stratigraphic (or diagenetic) trap. End_of_Article - Last_Page 245------------