Does Reproductive Potential of Red Snapper in the Northern Gulf of Mexico Differ Among Natural and Artificial Habitats?Glenn, Hilary Day 06 November 2014 (has links)
This study compares the reproductive potential of red snapper (Lutjanus campechanus) at artificial and natural habitats. Natural habitats are areas of vertical relief created from biogenic/geologic processes that are thought to be the historical centers of abundance for red snapper in the northern Gulf of Mexico. Red snapper were collected from 2011 to 2013 at three natural habitat sites and two artificial habitat oil and gas platform sites. The mean gonadosomatic indices (GSI), maturity at size and age, spawning indicators, batch fecundity, spawning frequency, and annual fecundity for red snapper at each habitat were analyzed to examine reproductive potential among sites and habitats. Results indicate red snapper on natural habitats exhibited higher mean GSI than those on artificial habitats during peak spawning season. Female red snapper on natural habitats showed 98% maturity, compared to 52% maturity of females on artificial habitats. These data support previous observation of demographic differences in red snapper reproduction between natural and artificial habitats. The differences observed may be due to red snapper at natural habitats being in better nutritional condition than red snapper on artificial habitats, thus allowing red snapper on natural habitats to invest more energy in reproduction and less energy towards rapid growth early in life.
Hurricane-Induced Geologic Change and Palynological Assessment of a Rapidly Subsiding Deltaic Environment in Coastal LouisianaNaquin, James Dustin 17 November 2014 (has links)
This study is focused on a paleoenvironmental history of a backbarrier coastal lagoon situated on the seaward margin of the Lafourche delta lobe in coastal Louisiana. A 2.2 meter long sediment core (Core BC 53) was collected from a mangrove-covered land strip on the northern margin of Bay Champagne, and was studied using pollen analysis, Loss-on-ignition (LOI), X-ray Fluorescence (XRF) analysis, and Cesium-137 and radiocarbon dating techniques to establish sediment stratigraphy and core chronology. Bay Champagne, a backbarrier lagoon formed during the evolution of Bayou Lafourche, has shown to be highly sensitive to geomorphological and vegetation changes induced by sea-level rise as noted by palynological, paleotempestological, and sedimentological records. In addition to capturing the rise and fall of the Lafourche delta lobe, Core BC 53 also preserved hurricane-induced sedimentary record. Pollen data revealed that Bay Champagne is mainly characterized by coastal marsh taxa. Freshwater marsh was dominant during the active period of the Lafourche delta about 1600 years ago. This was followed by a shift to salt marsh during its deterioration phase around 300 years ago. Avicennia germinans (black mangrove) emerged within the stratigraphy around 1880 A.D., which shows a direct correlation to relative sea-level rise. LOI and XRF data uncovered the presence of four hurricanes. Storm layers were not overwashed from the beach barrier due to its far distance from the coring site; however, these sedimentary signatures originated from the center of Bay Champagne and fluvial regions north of the lagoon. The distinct increase in charcoal concentration and decrease in arboreal pollen following Layer B implies the occurrence of wildfires induced by the hurricane. This is comparable to the results in Liu et al. (2008), which recorded three hurricane-induced fire linkages in coastal Alabama. Geological changes caused by Hurricane Isaac (September 2012) are found in the upper 3 cm of the core. This storm produced extensive fluvial flooding to the area as shown by LOI and XRF. These findings from Hurricane Isaac may provide a modern analog for interpreting the impacts of prehistoric hurricanes in sediment stratigraphic studies from this coastal region.
Legacy Phosphorus Implications in the Lake Pontchartrain Estuary Sediment Due to the 2011 Bonnet Carre Spillway OpeningNguyen, Nhan Thanh 21 November 2014 (has links)
Phosphorus (P) is an essential nutrient for life and excess P in aquatic systems can trigger algal blooms. Nutrient-rich Mississippi River water is diverted into the Lake Pontchartrain estuary (LPE) periodically through the Bonnet Carré Spillway (BCS) to avoid downstream flooding to the city of New Orleans, Louisiana and can significantly increase the internal P load in the sediment. A sequential P fractionation procedure was performed on sediments collected before the opening and after the closing of the 2011 BCS operation to understand the role of these large river diversions on P dynamics. Before the 2011 BCS opening, 10,368 Mt of P were found in the 0-10 cm sediment interval of the LPE. After the closure of the spillway, 13,293 Mt of P were measured in the 0-10 cm sediment interval. Total P significantly increased by 28% and a mass loading of 2,925 Mt of P was a consequence of the 42 days BCS opening. Sediment grain size analyzes revealed that majority of the finer sand and silt fractions were deposited near the BCS entrance, while the lighter clay fraction were transported tens of km towards the center of the LPE. Calculating the time for all newly added P from the 2011 BCS operation to flux out of the water column is important to understanding the impact on water quality of the LPE. Using a previously determined linear flux rate of ~517 Mt yr-1, it was estimated that ~6 years are needed to flux out the newly added sediment TP. While assuming a nonlinear model of flux rate, it is suggested that it would take a longer period of time to flux out all the newly P loaded from the sediments in the LPE. If the operations of these BCS opening are closely spaced in time (< 6 years), there will be an increase of P in the sediments which could lead to changes in the trophic status of the LPE. This increase of TP in sediments can lead to an increase in the frequency and persistence of harmful algal blooms for many years after the spillway opening.
Failed Agricultural Impoundments: An Interdisciplinary Assessment of Community Structure and Social ResiliencePeterson, Stacy Nicole 04 December 2014 (has links)
The remnants of the wetland reclamation era of the early 1900s are visible in the leveed, drained, and failed impoundments across the United States, and especially in coastal regions. The common themes of their history are flooding, restoration, and sometimes - community resilience. The physical changes occurring during and after impoundment, and after failure includes subsidence, erosion, and flooding are well-documented. Here I construct an environmental history that integrates data on these physical changes with archival records, historical documents, site visits and personal interviews. The primary region of focus is Delta Farms - a failed agricultural impoundment in Lafourche Parish, Louisiana that was first farmed in 1909 and failed in 1971. It consisted of 4 agricultural units: one that was never drained, one that was drained but not farmed, and two that were farmed for different periods. Some of the physical data includes soil and water depth measurements in the flooded portions of the property. These physical measurements were combined to assemble an environmental history of the property that integrated the experience of individuals and community. The growth and declines in population, recreational activities, agricultural practices, occasional levee failures, and mineral recovery on the property can be related to sociopolitical decisions that shifted during its 61 year history. The accuracy and completeness of this re-creation of the Delta Farms environmental history was greatly enhanced by including residents as a source of observation. They gave insight into the rate of natural marsh recovery, the timelines of developmental activity, and of community resilience. The study was a great example of how to understand a community, the social dynamics driving environmental changes, and community reactions.
28 May 2015
This study applies a three-dimensional numerical model ECOM-si to simulate the circulation in the Wax Lake delta under winter cold front conditions. This model uses real topography and bathymetry of the area to reproduce tides and the circulation between December 2012 and January 2013, which captures a total of seven cold front passages. The model results demonstrate that the circulation in the Wax Lake delta area is significantly affected by the winter cold fronts. The major findings are: (1) Water fluxes in the delta distributary network are not solely propagated within the channels but also between the channels, indicating inundation process by water intrusion onto the saltmarshes, which accounts for ~25% of water flux. (2). The current flows follow the wind direction change. Along-channel current dominates while cross-channel water transport occurs at the southwester lobe during post-frontal passage. The long-term impact on sediment transport will be the lobe shift to southeastward and thus lead to a significant change in geomorphology in the delta. Water intrusion and a temporary reverse flow are observed from model results in the delta channel tip during prefrontal passage. (3) The cold-front-induced flushing event lasts 41-185 hours that flushed out 32% to 76% of total waters by seven cold front events. (4). Subtidal energy accounts for over 45% of total energy while tidal energy contributes to less than 25%. (5) Cold front-induced wind is the most important factor and dominates the hydrodynamic circulations of the Wax Lake delta in winter.
31 May 2015
The northwest Gulf of Mexico (Gulf) shelf-edge banks both provide unique hard bottom habitat and support the northernmost coral reefs on the North American continental shelf in a region that is generally characterized by low relief, soft sediments. The habitat value of many of these banks has led to their designation as Habitat Areas of Particular Concern (HAPC) and the Flower Garden Banks National Marine Sanctuary (FGBNMS). However, little is known about the fisheries resources and dynamics of the banks outside the FGBNMS. This study had three main objectives: 1) define reef fish assemblages at northwestern Gulf shelf-edge banks and determine if assemblages were related to the varied benthic habitats present at these features, 2) define large-scale fish distributions at these same banks and determine the influence of habitat and environmental factors on distribution, and 3) examine the trophic ecology of red snapper (Lutjanus campechanus), a common and highly prized reef-associated fish, at these features. Assemblage definition and relation to habitat was based upon baited underwater video surveys conducted across a range of depths and habitats. Four distinct reef fish assemblages were resolved at the shelf-edge banks, the distribution of which corresponded to benthic habitat zonation. The specific habitat characteristics of mud substrate and live cover most strongly related to species distribution. Spatial distribution of fish biomass and density at the scale of individual banks was assessed using a mobile hydroacoustic approach. The highest fish biomass and density were observed directly adjacent to hard substrate, but showed high variability with regard to site, season, and habitat zone. Red snapper trophic ecology was assessed using stable isotope analyses to examine both relative trophic position and extent among bank sites. Results indicated a consistent carbon source, but differences in basal nitrogen between mid-shelf and shelf-edge locations. Differences in isotopic, and presumable trophic, variability between banks was attributed to different red snapper size distributions, with larger individuals displaying higher isotopic variability. Results of this study indicate the less studied northwest Gulf shelf-edge banks harbor predictable, habitat-related fish species assemblages that show variable large-scale distributions.
Kormanec, Marshall James
15 June 2015
Fish otoliths are composed of inorganic calcium carbonate that aid in gravity and auditory reception. Substances permanently accrete to otolith surfaces in distinct temporal patterns of alternating opaque and translucent rings; these rings are direct proxies for a fishs age. The objective of my research is to demonstrate how otoliths can be used through time and space to estimate both age and growth of fish. I investigated the spatial differences in age distributions and growth models for red snapper, Lutjanus campechanus, at four natural shelf-edge reefs in the northwestern Gulf of Mexico. Red snapper cohorts ranged 1987-2010 cohorts, with the majority (91.69%) of individuals between 4 to 9 years (2001-2009 cohorts) of age. The mean age across all sites was 7.2 years, and the modal age was 6 years. The 2006-year class dominated the distribution (22.98%) and the modal cohort was 2005. Differences in the von Bertalanffy growth parameter k were not detected despite significant differences in mean-size-at age in older age classes. Results suggest that habitat quality may be paramount in investigating red snapper demographics at shelf reefs. In addition, I investigated the temporal differences in freshwater drum Aplodinotus grunniens, age and growth estimates between ancient and modern freshwater drum populations. Ancient otoliths were recovered from shell middens associated with the Tchefuncte culture and the modern otoliths were collected from the commercial fishery in southeastern Louisiana between 1987-1989. Ancient otoliths were radiocarbon dated to 650 BCE, separating the two populations by ~2,600 years. Both populations exhibited a truncated age structure but significantly differed in age frequency distributions and mean age estimates. Mean otolith weight-at-age estimates were similar when plotted against biological age. Estimates of growth rates were difficult to obtain due to low sample sizes in young and older freshwater drum age-classes and the interment of ancient otoliths. Results suggest that mean otolith weight-at-age may be the most appropriate method for modeling growth. Furthermore, fishery exploitation and fisher gear selectivity may have been similar between the Tchefuncte and modern commercial fishers, despite the common assumption that ancient fish populations reached greater sizes-at-age and exhibited faster growth rates.
Fish Biomass and Community Structure Around Standing and Toppled Oil and Gas Platforms in the Northern Gulf of Mexico Using Hydroacoustic and Video SurveysReynolds, Emily Marissa 25 June 2015 (has links)
There has been relatively little study of the efficacy of decommissioned oil and gas platforms as artificial reef habitats for fish assemblages in the northern Gulf of Mexico (GOM). A variety of fish species have been reported on these structures, but the species biomass distribution and community structure has not been studied thoroughly. Hydroacoustic and video surveys were conducted quarterly from June 2013 to June 2014 at three standing and two toppled oil and gas platforms located approximately 130 km off the coast of Louisiana at 90 m depth; to gain information about the spatial biomass distribution and community structure at standing and toppled platforms. The toppled platforms in our study became a part of the Louisiana Artificial Reef Program in 2002. Stereo and Go-Pro® cameras were utilized for video surveys, allowing us to record counts and lengths of fishes. Hydroacoustic surveys were used to define the spatial distribution of fish biomass (MVBS, SV) in relation to distance to 500 m from the center of each site and the depth distribution of the observed biomass. MVBS of fishes was highest when near the structure and declined rapidly as distance from the structure increased, leveling off to a background-noise level at 100 m from the structure. Additionally, fish MVBS was highest in the lower water column (>60 m) compared to the upper and middle water columns. The fish communities differed between depth layers in the water column, seasonally, and between structure types (standing/toppled), with red snapper (Lutjanus campechanus) as a dominant species present at both site types. Coupling the data from these methods revealed that even though fish MVBS remained consistent throughout all seasons, different species comprise the MVBS observed during different seasons and between different layers in the water column. Coupling non-destructive methods allows for rapid monitoring which can be helpful in determining how to effectively manage both the fishes around the structure and the structures themselves.
Oil and Gas Platforms on Ship Shoal, Northern Gulf of Mexico as Habitat for Reef-Associated OrganismsReeves, David Bradley 20 April 2015 (has links)
Nearshore Louisiana has experienced substantial changes within the last half-century, including the annual formation of the worlds second largest hypoxic zone and the construction of thousands of oil and gas platforms (rigs). Ship Shoal and its rigs may provide important substrate in nearshore Louisiana because rigs act as de facto artificial reefs and the shoals bottom waters were well oxygenated on 43% of days when surrounding areas were hypoxic. From July to September of 2014, fish assemblages and hydrography were compared at shoal rigs, rigs inshore of the shoal, and rigs offshore of the shoal, and stone crab populations were compared at rigs on and off the shoal. A camera array and YSI sonde were used to characterize fish assemblages and hydrography at shoal rigs, rigs inshore, and offshore of the shoal. Stone crab densities were estimated with visual counts, and their life history was characterized by removing a subsample of stone crabs for identification and measurements. Fish assemblage composition was significantly different between shoal rigs, rigs inshore, and rigs offshore of the shoal (P<0.05). The most notable difference between assemblages was greater contribution of demersal fishes at shoal rigs than rigs inshore and offshore of the shoal. Hypoxia was intermittent at shoal rigs and persistent at rigs inshore and offshore of the shoal. Mean hypoxia thickness (meters of hypoxic water) was significantly greater (P<0.05) at rigs inshore (2.6 m) and offshore of the shoal (3.1 m) than it was at shoal rigs (0.6 m). Crab densities were roughly twice as high on as they were off the shoal (mean 4.0 vs. 1.8 stone crabs/m2; P<0.05), and the carapace width where 50% of females were ovigerous was 26.4 mm smaller for females off than on the shoal (P=0.057). Shoal rigs and rigs in surrounding waters provide important substrate for reef- associated organisms, although higher contribution of demersal fishes and densities of SCs at shoal rigs than rigs in surrounding waters suggest that shoal rigs are of higher relative importance. These findings suggest that further mining of Ship Shoal and removal of rigs may be detrimental to reef-associated organisms in nearshore Louisiana.
Johnson, Ron (Ronald E.)
28 September 1971
The distribution of Antarctic Intermediate Water in the South Pacific has been examined using a model of horizontal advection, along the Sigma-t surface 27.10, with three point vertical mixing. The core of the Antarctic Intermediate Water mass was traced from the Antarctic Convergence northward. The charts used to describe the distribution were those of core depth, salinity, percentage composition, Equivalent Thickness, and acceleration potential. The percentage composition of Antarctic Intermediate Water in the entire water column for all stations was computed and the Equivalent Thickness determined. Intermediate water volume for the South Pacific was then calculated. North-South geostrophic velocities and transports were computed for two zonal sections. The model agreed quite well with the flow patterns reported by other investigators. The broad counterclockwise gyre in the central South Pacific, the flow into the Tasman and Coral Seas, the localized flow near New Zealand, and the suggestion of southward flow near the South American Coast are all indicated by the model. A previously unreported small, counterclockwise gyre in the southeast South Pacific was detected. The circulation within the small gyre is consistent wity flow over a variable bottom in the Southern Hemisphere. Antarctic Intermediate Water transport across selected sections indicate a northward flow of 10 x 10⁶ m³ sec⁻¹. A low salinity tongue was found on the salinity chart. This tongue extended northward, then westward, into the northern Tasman Sea. The salinity was over 34.50°/₀₀ in the center of this counterclockwise motion east of New Zealand. The isohalines in the southeast Pacific suggest the presence of the small counterclockwise gyre. A 20 percent drop in core percentage composition was noted in the 10 degrees north of the Antarctic Convergence. A large uniform area between 80 percent and 70 percent over the central portion of the central South Pacific was bounded on the north by a 20 percent drop near the equator, again supporting the general counterclockwise circulation. The Equivalent Thickness distribution showed a general lenticular shape, the thickest part lying in the center of the counterclockwise gyre east of New Zealand. The Equivalent Thickness distribution, as well as the core percentage, supported the hypothesis of little or no flow into the Tasman Sea from the south. The volume of intermediate water obtained from surface area integration of the Equivalent Thickness distribution was 59.44 x 10⁶ km³. This is approximately 16% of the water volume in the South Pacific. / Graduation date: 1972
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