Abstract
Chenier forests are hardwood communities associated with the Northern Gulf Coast that have been severely reduced due to anthropogenic impacts and natural disturbances, with one of a few fragments remaining on Grand Isle. While long-term studies on permanent resident species of these forests are lacking, box turtles, an understudied permanent resident of Grand Isle’s forest, are vulnerable to habitat loss. To better understand the status and habitat use of Grand Isle’s box turtle population, as well as the health of the forest they reside in, I conducted a systematic mark-recapture study from June 2020 to August 2021. Population estimates of survival, recruitment, capture, and recapture rates, as well as abundance, were obtained using a robust model framework. Additionally, turtle size, ground temperature, turtle temperature, activity, as well as canopy and understory cover measurements were recorded to assess size classes and habitat use. There were 84 total box turtle captures and 40 recaptures, resulting in 44 marked individuals (17 Females, 16 Males, and 11 Juveniles). Survival and recruitment were constant and estimated to be 0.99 and <0.01, respectively. Abundance (70-116) capture (0.024-0.053) and recapture (0.036-0.073) estimates all varied over time. Males were significantly larger than females for all size measurements (CL, CW, CH, PL); however, the largest females were proportionally heavier than males. There was no difference between presence and absence habitat measurements, however, several differences in canopy and understory cover were found within and between life stage and sex regarding activity and season. Results from my study serve as baseline data for Grand Isle’s box turtle population. Specifically, these results have provided population estimates and habitat preferences that can aid in the planning and implementation of management for chenier forests while accounting for a resident species.
  Abstract
The overuse and improper disposal of antibiotics results in antibiotic resistance. Louisiana ranks as the fourth highest state for number of antibiotic prescriptions, implying greater opportunity for the introduction of antibiotics into Louisiana’s natural ecosystems. This raises concern over the presence of antibiotic resistant bacteria (ARB) in waterways and potential health risks of antibiotic resistant infections to water recreationists. The purpose of this study was to monitor water quality, microbial ecology, and antibiotic resistance of water and biofilm on submerged plastics at two public boat launches in southeastern Louisiana. From June 2021 to June 2022, water and biofilm samples were collected once a month, in triplicates, from Pleasure Bend boat launch near Vacherie, and Attakapas Landing boat launch near Labadieville, Louisiana. Water quality metrics included nitrogen, ammonia, sulfate, phosphate, and organic carbon. Water samples were tested for total and fecal coliform abundance and the presence of ARB. The antibiotics tested for resistance include, meropenem, amoxicillin/clavulanic acid, erythromycin, tetracycline, sulfamethoxazole/trimethoprim, bacitracin, and penicillin. Water quality metrics for both sites showed similar seasonal trends for all metrics, except sulfate. Sulfate levels were significantly higher at Attakapas Landing for fall, winter, and spring. Out of 131 bacterial isolates studied from these two sites, 86% of them tested for antibiotic resistance with multi-drug resistance. Antibiotic resistance genes (ARGs) for sulfonamide (sul2), bacitracin (bacA) and ampicillin (ampA) were identified in bacterial isolates from water and biofilm samples at both sites. Molecular genetic diversity analysis identified distinct taxonomic diversity differences in biofilm bacteria compared to the planktonic bacteria in the surrounding water. Biofilm samples showed increased diversity at the phylum, genus, and species levels. The presence of ARB and ARGs in biofilms on aquatic plastics raises concern for the spread of iv antibiotic resistance from plastic pollution. Plastics can degrade to microplastics, which can easily enter the food chain, further spreading ARB and ARGs through the food web.
  Abstract
The Barataria-Terrebonne Estuary System in southeast Louisiana is a biologically productive wetland ecosystem that is bound to the west by the Atchafalaya River and to the east by the Mississippi River. This system experiences the highest land loss rates in the U.S., which have converted healthy, freshwater cypress swamp near Chauvin, Louisiana into a degraded brackish marsh with mostly shallow water. Marsh-terracing is a restoration strategy that has been employed across much of the Gulf South to combat high rates of wetland loss. Terraces were recently constructed in a 20-hectare marsh site near Chauvin to decrease wave energy, reduce wave fetch height, and provide flora and fauna with improved habitat. The terraces contain 3,658 linear meters of marsh edge habitat and were planted with 35,000 marsh grass plugs. various sampling methods were used to compare differences in abundance of flora and fauna at the restored marsh site for the years 2019 and 2020. Water temperature was significantly greater (p < 0.05) at inner terrace sites in summer 2020 compared to control marsh sites in fall 2020 and spring 2021. Spartina alterniflora, S. patens, and Phragmites australis are the three dominant vegetation species occurring at the marsh site. Of seven invertebrate species collected at the marsh site, Palaemonetes spp. were the most abundant, composing 65.5% of overall aquatic invertebrate species. Of nine small-bodied fish species collected, Cyprinodon variegatus was the most abundant and composed 58.0% of overall small-bodied fish species. Hyla cinerea was the predominant species encountered at frog pipes for both years. Nine species of anurans were recorded at the marsh site using frog call surveys, and H. cinerea was heard most frequently throughout the study and in greatest densities. Nerodia cyclopion was the most abundantly collected reptile and composed 72.1% of overall reptile species. A maximum 55 bird species were documented, totaling 5,352 individuals. Continued monitoring of this site will provide insight into how well various floral and faunal species colonize terraces in a restored marsh landscape.
  Abstract
Antibiotics are often released into the environment via disposal or excretion. A selection pressure is then initiated that leads to the acquisition of antibiotic resistance genes (ARGs) in environmental bacteria, thus encouraging the environmental spread of antibiotic resistance. The purpose of this study was to examine nutrient and antibiotic reducing capacity of the Point au Chene wetland that receives the city of Thibodaux treated sewage wastewater. Water samples were collected from four sampling sites along the wetland every month from May 2022 to April 2023, excluding October 2022–January 2023 due to seasonal closing of the site for hunting. Water quality was assessed at each stage of flow within wetland during summer and winter/spring seasons, including the input site, wetland midpoint, wetland endpoint, and a control site adjacent to the Thibodaux Sewage Plant. Water chemistry, coliform bacteria, and antibiotic concentrations were analyzed in triplicates. The results indicated antibiotic, coliform, nitrate, sulfate, and ammonia concentrations were significantly higher at the input site than other wetland sites throughout both seasons, supporting the value of wetland systems in water purification and nutrient reduction. The input site additionally expressed the highest amount of multi-drug resistance and bacterial diversity of all sites. ARGs have been identified throughout the wetland system, with Escherichia coli isolates testing positive for the ARGs bacA, sul2, and tetA, coding for resistance to bacitracin, sulfonamide, and tetracycline antibiotics respectively. Successful reduction of aforementioned nutrients, coliform, and resistance indicators are present within this natural assimilation wetland wastewater treatment system. The wetland has a positive impact of reducing the nutrients and ARB in the treated sewage.
  Abstract
Triclosan (5-chloro-2-(2,4-dichlorophenoxy)phenol) is an antibacterial and antifungal agent that is resent in many antibacterial detergents and surgical leaning treatment products. This antimicrobial compound is typically discharged from households and collected at the local sewage treatment plant. because triclosan inhibits phospholipid biosynthesis, it affects the microbial population that perform waste degradation. Sewage treatment plants are the major reservoir of triclosan as the wastewater from various households are discharged and treated in the local sewage treatment plant. This study was conducted to determine whether triclosan degradation occurs in the anaerobic digester of the Thibodaux Sewage treatment Plant. Bacterial enrichment cultures were developed under various electron acceptor conditions including aerobic, nitrate-reducing, sulfate-reducing, and mixed electron acceptor condition using basic mineral salt (BMS) medium with triclosan as the sole source of carbon and under co-metabolic condition with glucose as a main substrate. We found that the bacterial consortia collected were not inhibited by 100 ppm of triclosan. Triclosan was removed in both co-metabolic conditions and sole carbon source conditions under sulfate-reducing and mixed electron acceptor conditions. The sole carbon source condition under sulfate reducing and mixed electron acceptor treatments exhibited complete degradation of triclosan, and the sulfate-reducing co-metabolic condition exhibited approximately 83% carbon removal. One major metabolite was eluted in the high performance chromatograph analysis indicating triclosan degradation by the bacterial consortium. The molecular analysis of the consortium showed wide biodiversity of bacteria including roteobacteria, Euryarchaeota, Bacteroidetes, Caldiserica, Firmicutes, Acinitobacteria, Sacharibacteria, Tenericutes, Aminicenantes, and Acidobacteria with Proteobacteria being the dominant group.
  Abstract
Crayfish are key components in freshwater ecosystems and trophic webs, fundamental in determining ecosystem structure and function, and are indicators of water quality and biodiversity. However, many crayfishes are imperiled due to anthropogenic activities and in Louisiana there is a paucity of basic ecological information on most crayfishes, including species of greatest conservation need (SGCN). This lack of crayfish distribution and habitat preference information makes conservation actions difficult for scientists and resource managers. Therefore, the purpose of this project was to examine the distribution, population status, and habitat requirements for crayfishes in the Tickfaw, Tangipahoa, and Tchefuncte River basins in Louisiana. Fifty-five 1st to 4th order streams were sampled from June to October in 2020 and 2021 using backpack electrofishing, kick seining, and dipnets. A total of 2,326 crayfishes representing ten species were collected. Although there was no significant difference in crayfish diversity among river basins or ecoregions, Pinelands Creek Crayfish Procambarus vioscai was the most abundant and common species collected (878 individuals in 28 streams). The Pontchartrain Painted Crayfish Faxonius hobbsi, a SGCN, was found in all three river basins but was one of the rarest species encountered with only 56 individuals collected. Multivariate analysis of variance indicated a significant difference in habitat characteristics between streams with and without F. hobbsi (Wilks’ Lambda = 0.52, P < 0.001). Streams with F. hobbsi were characterized by sandy substrate, significantly higher dissolved oxygen (F1,53 = 9.95, P = 0.003), discharge (F1,53 = 7.38, P = 0.009), and in-stream wood (F1,53 = 13.04, P = 0.001), and significantly lower specific conductance (F1,53 = 4.06, P = 0.049), turbidity (F1,53 = 10.15, P = 0.002), and temperature (F1,53 = 14.58, P < 0.001) compared to streams without F. hobbsi. Additionally, F. hobbsi did not co-occur in streams with Red Swamp Crayfish Procambarus clarkii. There was no significant difference in any habitat variables among F. hobbsi, Lowland Painted Crayfish F. palmeri, and P. vioscai and all three species were associated with relatively high-quality aquatic habitats. Conversely, P. clarkii, Southern White River/White River Crayfish P. zonangulus/acutus, Shrimp Crayfish F. lancifer, and Cajun Dwarf Crayfish Cambarellus shufeldtii were associated with lower quality habitat characteristics. Results from this study provide novel information on crayfishes and habitat requirements, including the SGCN F. hobbsi. The information collected will aid state and federal resource managers with species conservation assessments and preservation efforts, help prioritize stream and watershed locations for future sampling efforts, and establish a quantitative biological and ecological data set on crayfishes in Louisiana.
  Abstract
With the introduction of the Giant Apple Snail Pomacea maculata to Louisiana in 2006, there came a need to understand how this invasive species and the estuary habitat respond to one another. While several reports on Apple Snails outside of this estuary exist, there remains a need to study the geographical range of the snails and the predatory capabilities of other species on the snails in the Barataria-Terrebonne Estuary System (BTES). The purpose of this research was threefold: document the range of the Apple Snail in the BTES, explore the potential of the reproductive anatomy of the Apple Snail as a possible biomarker for reproductive health, and test whether native decapods would act as predator species on the egg and juvenile stages of the Apple Snail. We conducted a presence/absence survey to document the range of the snails in 20 major waterways of the BTES. We identified snails in 19 of the 20 waterways and developed a map of the range in the BTES. We developed an anatomical biomarker using secondary sex characteristics compared to somatic characteristics. The male index compared the penile sheath length to the operculum length, and the female index compared the albumen gland mass to the total body mass. We collected and dissected 931 snails (385 males and 546 females). The males exhibited a difference (F = 9.219, P < 0.0001) in the average penile sheath to operculum length index among sites. Likewise, the female albumen gland to total wet mass index varied among sites (F = 40.44, P < 0.0001) and the female albumen gland to total dry mass index varied among sites (F = 16.90, P < 0.0001). In the predation survey, we observed the predatory abilities of Blue Crabs Callinectes sapidus, Longwave Fiddler Crabs Uca longisignalis, and Red Swamp Crayfish Procambarus clarkii on snail eggs and juveniles. Blue Crabs consumed (F = 29.09, P < 0.0001) more eggs than fiddler crabs and crayfish. On the other and, when presented with juveniles, crayfish consumed (F = 145.36, P < 0.0001) more than Blue Crabs and fiddler crabs. The results of this research provided an updated geographic range of Giant Apple Snails in the BTES in the month of July 2020 with a suggested salinity barrier at the southern limit of the range. This study provides baseline information on Giant Apple Snail anatomy as a biomarker for reproductive health using two developed reproductive indices. Finally, this study identified three new decapod predators of Giant Apple Snails at previously understudied life stages: eggs and juveniles.
  Abstract
Zinc is an essential but toxic metal with both natural and anthropogenic sources. Zinc has been reported to be present in crustacean exoskeleton, but it has remained unknown as to when zinc is incorporated into the shell during the molting cycle and the effects zinc has on exoskeleton properties. This study was conducted to identify what molting stage and pathway was used for zinc incorporation into the exoskeleton of the blue crab, Callinectes sapidus, and to identify deleterious effects of zinc incorporation on the exoskeleton. It was hypothesized that zinc would be incorporated into the shell during the mineralization phase using calcium transporters, which would inhibit exoskeletal calcification. Post-ecdysial blue crabs were given two injections of zinc in the form of zinc chloride dissolved in Pantin’s crustacean saline at the arthrodial membrane at three treatment levels: 0.0, 1.0 and 5.0 μg Zn/g wet weight. Exoskeletal and hemolymph samples were then analyzed for zinc, calcium, and magnesium content. Gill, muscle, and hepatopancreas samples were analyzed for zinc only. Epidermis samples were analyzed for carbonic anhydrase activity. The results showed that the injection dose of 1.0 μg Zn/g wet weight resulted in significant accumulation of zinc in the exoskeleton. A significant reduction in exoskeletal calcium content in crabs treated with 1.0 or 5.0 μg Zn/g wet weight was also observed. Discussion on the mechanisms driving zinc’s incorporation into the exoskeleton as well as the inhibition of exoskeletal calcification is presented. Additionally, for the soft tissues examined, significant zinc accumulation was only observed in the hepatopancreas following zinc treatment. This study is the first to present evidence that zinc is deposited to the exoskeleton during post-ecdysial mineralization and inhibits postmolt exoskeletal calcification in a crustacean.
  Abstract
River-floodplain ecosystems provide important spawning, feeding, and nursery habitat for large-river fishes. Anthropogenic modifications can reduce river-floodplain connectivity, limiting access for fishes, and influencing community structure and trophic ecology. The purpose of this study was to identify changes in the trophic ecology of gars (Lepisosteidae), primarily piscivorous fishes often dependent on floodplain habitats, during seasonal inundation. Shifts in trophic ecology were evaluated using stable isotope analysis of fin tissue. Carbon (δ13C) was used to determine habitat use and nitrogen (δ15N) to estimate trophic position. Fin tissue clips (n = 198) were collected from four species of adult and young of the year (YOY) gars, Longnose Gar Lepisosteus osseus (n = 55), Shortnose Gar L. platostomus (n = 87), and Spotted Gar L. oculatus (n = 54), and Alligator Gar Atractosteus spatula (n = 2) in riverine and floodplain habitats of Loch Leven, a restored Mississippi River floodplain in Wilkinson County, Mississippi. Gars on the floodplain (16.25 ± 0.09‰) were significantly (F-ratio = 79.42, df = 1, P < 0.001) depleted in δ15N relative to gars in riverine habitats (17.37 ± 0.08‰). Adult Longnose Gars exhibited the greatest δ15N enrichment (17.44 ± 0.11‰), followed by Shortnose (16.60 ± 0.08‰) and Spotted Gars (15.97 ± 0.15‰). The δ15N value of YOY (16.41 ± 0.08‰) wassimilar to adults, but δ13C (-28.47 ± 0.15‰) varied significantly (F-ratio = 157.70, df = 1, P < 0.001), reflecting that of floodplain baseline organisms (-27.86 ± 0.33‰). These results indicate that floodplain access influences gar trophic ecology. Low δ15N of gars on the floodplain suggests a lower trophic position relative to gars in riverine habitats. Similarities in δ13C between YOY and baseline organisms indicate YOY originated on the floodplain and capitalized on abundant floodplain resources. Understanding the influence of river-floodplain connectivity on trophic ecology of aquatic organisms can better inform restoration, conservation, and land management practices.
  Abstract
Model organisms (e.g. Fruit Fly Drosophila melanogaster, Laboratory Rat Rattus norvegicus) are species used to investigate biological processes that are applicable to humans. The Spotted Gar Lepisosteus oculatus is abundant in Louisiana waters and can be spawned in the laboratory. The Spotted Gar has emerged as a new model organism that has enhanced our ability to compare more traditionally used fish models such as Zebrafish Danio rerio with the human genome. Until recently, Spotted Gars were only spawned in the lab during the natural spawning season (spring, in-season spawn), producing a single cohort of research specimens each year. New techniques, developed at Nicholls State University, have made it possible to also spawn Spotted Gars in the winter (out-of-season spawn), potentially doubling the availability of specimens to the research community. To assess the “quality” of Spotted Gars produced from an out-of-season spawn, I used a common garden experiment to compare growth and development of young-of-year fish spawned in spring and winter 2019 for 65 days. Growth (length and weight) and morphometric ratios (e.g. head length:standard length) were used to compare development of in-season and out-of-season spawns. Results indicated growth rate of winter Spotted Gars (1.07 mm/day and 6.1 mg/day) was not different from spring Spotted Gars (1.12 mm/day and 8.2 mg/day). Our findings suggest that Spotted Gars spawned out-of-season are of similar quality to Spotted Gars spawned in-season, and can greatly increase the number of specimens available for research each year, further supporting the use of Spotted Gars as biomedical model organisms and adding value to an abundant Louisiana natural resource.
  Abstract
Understanding the trophic ecology of populations is important for the conservation and management of species. Stable isotope analysis (SIA) can be a powerful tool for investigating trophic ecology and how energy flows through an ecosystem. Muscle tissue is preferred for SIA in fishes due to its intermediate turnover rate, however, sampling muscle is often lethal. I evaluated the feasibility of a fin clip model (FCM) using fin tissue as a non-lethal alternative to muscle tissue for SIA (nitrogen, δ15N and carbon, δ13C) in the Spotted Gar Lepisosteus oculatus and Alligator Gar Atractosteus spatula. I also used stomach content, trophic level, and life history characteristics (e.g. age, size) of Spotted Gars from the upper Barataria Estuary (UBE) and Atchafalaya River Basin (ARB) to evaluate the robustness of the FCM. Muscle tissue plugs and fin tissue clips were collected from Spotted Gars (n = 104) and Alligator Gars (n = 16) at four localities in southeastern Louisiana in 2019. Spotted Gars were collected seasonally from the UBE (pre-spawn, spring, summer, fall, and winter) and ARB (fall and winter). Both Alligator Gars and Spotted Gars showed strong positive Pearson’s correlations in δ15N and δ13C between fin and muscle tissues, and linear regression confirmed correlations were significant (Spotted Gar; δ15N: R2 = 0.94; δ13C: R2 = 0.97, Alligator Gar; δ15N: R2 = 0.74; δ13C: R2 = 0.94). The FCM was not significantly affected by size, age, or sex. Mean trophic level for ARB Spotted Gars in fall (3.51 ± 0.05) was significantly higher than fall UBE (3.03 ± 0.06), but ARB winter (3.99 ± 0.04) and UBE winter (3.83 ± 0.09) mean trophic level was not significantly different. Overall, my results suggest that fin tissue can be used as a non-lethal surrogate for muscle tissue for both Spotted and Alligator Gars. Understanding the trophic ecology of these key Louisiana predator populations can better inform conservation and management practices for the species.