An extensive search for data on life-history and ecological variables was conducted for a representative number of the species within the family Lutjanidae. After creating different databases and standardizing all data, these variables were examined in statistical, correlation and graphic analyses. Additionally, a series of Principal Component Analyses were used to examine patterns among variables. Life-history variables included age at length zero, asymptotic length, maximum length, longevity, asymptotic weight, length at maturity, age at maturity, reproductive life span, growth rate and mortality rate. Ecological variables included latitudinal and vertical distribution, habitat selection (represented by substrate type), and spawning seasons. The feeding habits of snappers were examined after determining the most common items reported in the literature and summarizing them in ten categories. Results indicated that life-history variables related to the size of the species were highly correlated, supporting the findings of other studies that length at maturity is dependent on asymptotic length. Longevity and reproductive life span were also highly correlated, while longevity and age at maturity had a low correlation, indicating that maturity among snappers is independent of life span and with relatively low variation among species. A review of the geographic and vertical distribution of snappers suggests that pre-settlement larvae in several species may exhibit strong nursery habitat selection, and that adult snappers have distinctive vertical distributions. Finally, based on the variability of prey items found in snapper diets, two basic feeding strategies were evident, species in the subfamily Lutjaninae feed mainly on benthic organisms, mainly crustaceans; while species in the subfamily Etelinae feed in the water column on a variety of pelagic fishes and invertebrates.

The diets of a transitory fish (spotted sea trout, Cynoscion nebulosus) and a fish with presumed greater site-fidelity (pinfish, Lagodon rhomboides) were analyzed with respect to habitat. Sampling occurred in Barataria Bay, Louisiana between May 2003 and May 2004. Spotted sea trout were caught using gillnets, and pinfish were caught using baited fish traps. Each gear was used on three habitats: mud bottom, oyster shell, and marsh edge. In addition, sampling for spotted sea trout was repeated at three locations along a salinity gradient. A total of 175 spotted sea trout stomachs and 137 pinfish stomachs were examined. Seventeen prey species were identified in the guts of spotted sea trout, and thirteen species were identified for pinfish. Fifty-three percent of spotted sea trout stomachs were empty, and 37% of pinfish stomachs were empty. Unidentifiable fish and brown shrimp(Farfantepenaeus aztecus) were consistently the most important prey items for spotted sea trout in weight, frequency, and caloric value. Plant material, detritus, and small amounts of fish and shrimp, were consistently most important for pinfish by weight, frequency, and caloric value. The diet of spotted sea trout caught adjacent to marsh edge had the least dietary overlap with fish from other habitats, especially during winter and spring. The diet of pinfish caught over shell had the least dietary overlap with conspecifics from other habitats. Dietary breadth for spotted sea trout was similar across habitats and lowest in winter. Dietary breadth for pinfish was lowest on the shell habitat and in fall. Neither habitat, season, water quality (i.e., dissolved oxygen, temperature, salinity), nor any other effect could be shown to be statistically significant in distinguishing the diet of either fish using Analysis of Variance (ANOVA) and Analysis of Similarities (ANOSIM) statistical techniques. Diets of these two fish were not notably diverse, but the dietary breadth for both fish species was high, suggesting that of those prey items consumed, there was no strong preference among the prey. This may be attributable to the transitory nature of the fish and the ubiquity of some of the prey types across habitat types.

Elevated soluble aluminum concentrations can adversely affect plant growth. During a drought, wetland soils may experience higher than normal soluble aluminum due to the oxidation of metal sulfides and resulting decreases in pH, which mobilizes metallic cations. Louisiana coastal salt marshes were subject to a record-setting drought in the winter and spring of 2000 which was coincident with the die-off of large expanses of salt marsh, termed " brown marsh ". Spartina alterniflora was the primary plant species affected. However, because some individuals within large areas of die-off survived the brown marsh event, they may have been the more resistant genotypes. To determine if genotypic resistance to aluminum existed, six genotypes of the common salt-marsh cord-grass Spartina alterniflora, five surviving genotypes, and a commercial variety (Vermillion), were dosed with aluminum chloride (AlCl₃) at concentrations ranging from 0.2 mM to 10.8 mM. No death was observed in any of the genotypes at aluminum concentrations as high as 10.8 mM, although growth rates decreased to near zero. The results of this study indicate that, as a species, the resistance of Spartina alterniflora to aluminum may surpass the threshold of any plant species studied to date. All genotypes in the experiment were found to tolerate extremely high concentrations of aluminum, although declines in stem elongation rate and cumulative stem height were evident in all Al treatments. I estimated the differential aluminum tolerance by using the first significant decrease in growth rate when the genotype x concentration effect was significant. The first significant decrease approach had the best resolution for determining genotype variability when used with the stem elongation data. Although insufficient evidence exists to determine if aluminum toxicity caused the brown marsh event in Louisiana, based on the results of this thesis, the aluminum concentrations would have had to reach extremely high levels to have been the sole cause of the brown marsh dieback.

Copepods are important components of marine ecosystems. Understanding copepod population dynamics can help interpret variations in both primary producers and higher trophic levels. Egg production, stage duration, and stage-specific mortality rates are key parameters describing copepod population dynamics. Estimation of stage-specific mortality is complicated due to a complex life history, patchiness, and sampling biases. This study was undertaken to quantify the population dynamics of the copepod <i>Clausocalanus furcatus</i> in the northern Gulf of Mexico and to assess the utility of available mortality estimation methods in a highly advective environment. Zooplankton samples were taken every 12h from March 18-April 6, and May 15-June 9, 2003 from an offshore petroleum platform using a 153μm net and a 30L Niskin bottle to characterize the mesozooplankton assemblage. Incubation experiments were conducted during June-July 2002, March-April 2003, and May-June 2003 to measure egg production rates and stage durations. Stage-specific mortality rates were estimated using the horizontal life table (HTL), vertical life table (VTL), quadratic programming method (QPM) and inverse matrix method (IMM). Mesozooplankton communities in the study area were influenced by the Mississippi River plume. Field estimates of the mean egg production rate of <i>C. furcatus</i> were lower than measurements from lab incubation experiments. Egg production rates did not appear to be limited by food availability. A complete generation time ranged from ~13-20d. Early naupliar stages had shorter durations than late copepodite stages. Comparisons among HTL, VTL, QPM and IMM showed that the HTL and VTL had the disadvantage of producing negative mortality estimates, while the QPM likely overestimated mortality rates. Simulation experiments indicated that variability in stage abundances was a key factor affecting estimates of copepod mortality by the QPM and IMM techniques. Neither the QPM nor the IMM performed well when stage abundance variability was high. IMM estimates of instantaneous egg mortality rates were 1.30d^-1 in March-April and 1.60d^-1 in May-June. While instantaneous mortality rates for NI-CCIV stages ranged from 0.02 to 0.18d^-1. Simulated populations using the mortality rates estimated from the IMM technique were consistent with observed field population trajectories.

Rice fields are a major source of the greenhouse gases methane (CH₄) and nitrous oxide (N₂O) and contribute to nitrate (NO₃^-) pollution in waters. Ferric iron (Fe³⁺) and manganic manganese (Mn⁴⁺) are two intermediate alternative electron acceptors (AEAs) capable of regeneration in freshwater soils. In this investigation, the influences of iron-centered intermediate redox processes on NO₃^- reduction and CH₄ formation in rice soils were studied using soil slurries, soil columns, and potted rice. Reduction of Fe³⁺-centered intermediate AEAs was mainly mediated by obligate anaerobes relying on fermentation products. Ferric iron reducers are bioelectrochemically active, supporting bioelectricity generation through a fuel cell process from the flooded soil coupled to the reduction of O₂ or NO₃^- in the overlying water. As a major electron accepting process in anaerobic carbon decomposition, Fe³⁺ reduction stimulated N₂O production but had little influence on overall NO₃^- reduction in the homogenized soil slurries under near-neutral pH conditions. In the flooded soil column and pot experiments, intensification of iron-centered intermediate redox processes under amendments of iron and/or manganese oxides changed the fate of NO₃^- in the overlying water, decreasing heterotrophic denitrification and increasing NO₃^- percolation and N₂O emission. Ferric iron reduction competitively suppressed methanogenic activity in the homogenized soil slurries. The diffusion of the stronger oxidants O₂ and NO₃^- controlled temporal and vertical variations of iron-centered intermediate redox processes, which subsequently controlled temporal and vertical variations of methanogenic activity in the flooded soil columns. In the pot experiment, Fe³⁺ reduction had small effect on CH₄ emission in the early season when CH₄ emission was low but effectively reduced CH₄ emission after midseason drainage intervals through Fe³⁺ regeneration. The roles of iron-centered intermediate redox processes need to be considered in the evaluation and predication of NO₃^- reduction and CH₄ formation in rice fields.

Sidescan Sonar, chirp sonar sub-bottom profiles, and grab samples were collected on the north-central Gulf of Mexico continental shelf as part of an interdisciplinary study mapping juvenile red snapper habitat. Demarcation of essential fish habitat for juvenile red snapper (Lutjanus campechansis) in the Gulf of Mexico is considered critical for effective management of this valuable species. The first goal of this study was to map and describe the geology of this region. The second goal was to attempt to relate variations in geology to juvenile red snapper abundance and distribution. Sidescan mosaics were created for ten polygons, ranging in size from 2 to 20 km² on the inner to middle shelf south of Mississippi-Alabama, in water depths of 17-40 m. Geological observations delineated three contrasting seabed types: (1) linear to patchy shell regions on the inner-middle shelf, (2) muddy sand sheets on the middle shelf, and (3) prodeltaic muds in the southwest of the study area, marking the eastern extent of recent shelf deposits from the modern Mississippi delta. The shell ridges stand 1-3 m above the surrounding seabed, and may extend 200 m across. They are composed of > 50% CaCO₃, including shell fragments from both estuarine and marine taxa, and contrast sharply with adjacent muddy sands containing minor shell. Radiocarbon dating of shell material, along with the geological characteristics of the ridges suggests that they are remnants of Holocene coastal environments. This region was previously described as either an extension of the MAFLA sand sheet or a transitional zone between the MAFLA sands and prodelta muds (Ludwick, 1964). In the present study, we identified a range of geological features of estuarine, shoreface, and wholly marine origin. The diversity of deposits described records a wide range of geological processes active from early-middle Holocene to recent time. The integration of geological observations with coordinated biological observations reveals that geologic structures and sediment composition on the northern Gulf of Mexico continental shelf are major controls on the distribution of juvenile red snapper (Patterson et al, in press), and record both coastal depositional histories and open-shelf processes active during Holocene transgression.

The northern Gulf of Mexico (GOM) is one of the most productive oil and gas exploration areas in the world, currently containing approximately 3,800 offshore platforms. These platforms serve as artificial reefs in shallow water, which until their introduction was nearly devoid of shallow hard substrata. The question is raised whether this newly available substrate could help expand coral populations in the GOM. In this study, I examined adult scleractinian corals on oil and gas platforms in the northern GOM, in the vicinity of the Flower Garden Banks (FGB; approximately 180 km SE of Galveston, Texas) and attempted to determine the degree of genetic affinity among the natural and platform populations there. Adult coral tissue samples were collected from seven platforms surveyed in the region of the FGB at a depth range of 0-30 m. The three most abundant scleractinian, hermatypic species were sampled: Madracis decactis, Diploria strigosa, and Montastraea cavernosa. Genetic variation was revealed by Amplified Fragment Length Polymorphisms (AFLPs), a DNA-fingerprinting technique based on the polymerase chain reaction (PCR). This tool successfully distinguished between closely related colonies derived from populations on different platforms and on the two Flower Garden Banks. AMOVA analyses indicated that the East and West FGB were homogeneous for Madracis decactis and Diploria strigosa; however, the Montastraea cavernosa populations at the two banks were significantly different. Randomized data sets of two Madracis decactis populations were run with AFLPOP using a minimum log-likelihood difference of zero and one. These analyses determined that a log-likelihood difference of one is a more conservative and more reliable option, and all subsequent analyses were run using this setting. AFLPOP analyses showed that Montastraea cavernosa at the two banks was highly self-contained, indicating a possible high degree of self-seeding with regard to this species. It appears that Madracis decactis, a brooding species, is highly effective at dispersing to neighboring habitats over distances of kms to tens of kms. By comparison, Diploria strigosa and Montastraea cavernosa, both broadcasting species, are not. They may be more effective at larger scale dispersal, but this remains to be demonstrated.

The Mississippi Sound is a bar-built estuary that parallels the Mississippi Coast. It is bounded on the west by the St. Bernard lobe of the Mississippi River delta, Mobile Bay to the east, and the Gulf Coast barrier islands to the south. Few studies have investigated the late Holocene history of Mississippi Sound. In the present study, historical deposition in the Sound has been investigated using core data collected throughout the western, central, and eastern Mississippi Sound. The sediments within Mississippi Sound compose a complex depositional system that have responded to changes in sea level and hydrodynamics. Two factors that influence the wave dynamics within Mississippi Sound are changes in water depth and exposure to the open Gulf of Mexico. Decreases in water depths have an inverse relationship to the shear velocity produced by waves. Thus, by decreasing water depth from 3 m to 2.5 m, the shear velocity (U*), produced from a wave with H = 0.9 m and T = 4 s, would increase from ~0.006 m/s to 0.008 m/s. These changes may be recorded in the sedimentary fabric as changes in the sedimentary facies from a low-energy muddy facies to a higher-energy sandy facies. However, increased exposure to the open Gulf of Mexico allows for larger deep-water waves to impact the Sound. Therefore, by exposing Mississippi Sound to increased wave energy from the Gulf of Mexico, conditions become favorable for the deposition of the higher-energy sandy facies in the deeper water of Mississippi Sound. The sedimentary fabric and geochronology data of recent deposition suggest that physical processes actively rework the sediment in the top 5 cm of the sea-bed; however, biological processes continuously rework the sediment to a depth of 10-12 cm resulting in the destruction of most of the physical stratification. Tropical cyclones impact the sedimentary fabric such that they are recorded as sandy event beds within a muddy matrix. Approximately 8-26% of the sediment column was deposited by recordable storm events in the Western Mississippi Sound, whereas smaller storm events and typical estuarine processes deposited the other 74 92% of the sediment column.

The need for effective marsh restoration techniques in Louisiana is a pressing issue as the state continues to lose coastal wetlands. Returning spoil banks to canals, known as "backfilling", is an attractive restoration option because it restores marsh, prevents future wetland loss, and is cost effective. The direct conversion of marsh to canals and spoil banks accounted for over 22% of Louisiana's wetland loss from 1930 to 1990, and the indirect losses associated with canal dredging are even larger. The restoration success of 30 canals, backfilled twenty years ago, was examined in this study and compared to restoration success shortly after backfilling. Ultimately, the success of backfilling was controlled by the amount of spoil returned to the canal and the position of the canal in the marsh. Up to 95% of the spoil area was restored to marsh when the spoil banks were adequately removed, but only 5% of the spoil area was restored at sites where spoil removal was poor. Restoration of organic matter, bulk density, and water content of the former spoil areas was also constrained by the adequacy of spoil removal. Backfilling restored 80% of the organic matter and 94% of the bulk density and water content after twenty years at sites where spoil was properly removed. The plant species on the former spoil areas often did not match those of the surrounding marsh, and the differences were directly correlated with the amount of spoil removed. Canals backfilled in areas of more intact marsh showed greater restoration success than canals backfilled in highly degraded marshes. This study indicates that the benefits of backfilling continue to increase over time, although complete restoration will take longer than twenty years, particularly for soils. Improving the completeness of spoil removal, coupled with appropriate site selection, could speed up the restoration process and enhance the success of future backfilling projects.

The cownose ray, Rhinoptera bonasus, is an elasmobranch commonly observed throughout the Gulf of Mexico. Cownose rays appear to be sensitive to water temperature. I performed laboratory experiments and collected field data to obtain basic life history information, and used the information to configure an individual-based bioenergetics model. The bioenergetics model was coupled to a matrix projection model, and the coupled models were used to predict how warmer and cooler water temperatures, compared to current conditions, would affect the growth and population dynamics of the cownose rays. The life history study determined weight at age, maturity by weight, and fecundity for cownose rays. Verified vertebral age estimates ranged from 0+ to 18+ years. Likelihood ratio tests indicated that a combined sexes Gompertz model best described the growth of cownose rays. A relationship between maturity and weight was estimated; annual fecundity was determined to be one pup. The laboratory experiments resulted in the estimation of standard oxygen consumption rate as a function of weight and temperature, and a Q10 value of 2.33. The bioenergetics model predicted that rays would have a slower growth rate and reach smaller average weights at age (9.6-16.8% smaller) if they inhabited 2oC warmer water than baseline (current) conditions, while individuals would grow faster and attain heavier weights at age (13.4-17.2% heavier) under a 2oC cooler scenario. Changes in growth rates under the warmer and cooler conditions also lead to changes in age-specific survivorship, maturity, and pup production, which I used as inputs to a matrix projection model. Faster growth of individuals under the cooler scenarios translated into an increased population growth rate (4.4-4.7%/year versus 2.7%/year under baseline), shorter generation time, and higher net reproductive rates, while slower growth under the warmer scenarios translated into slower population growth rate (0.05-1.2%/year), longer generation times, and lower net reproductive rates. Elasticity analysis indicated that population growth rate was most sensitive to adult survival. Reproductive values by age were highest for intermediate ages. The combination of coordinated laboratory experiments, field data collection, and coupled individual-based bioenergetics and matrix projection models provides a powerful approach for relating physiology to demographic responses.