Theses @ Nicholls State University

 
Abstract
Connectivity of large rivers with their floodplains can benefit riverine fishes by providing access to food, additional habitat, and spawning areas. However, due to anthropogenic modifications, floodplain habitats are often disconnected from their associated rivers, potentially limiting ecosystem function. Two restoration projects addressing this issue were initiated in 2020-2021 at floodplain sites in the Lower Mississippi River Basin: Loch Leven (LL) in Mississippi, and Richard K. Yancey Wildlife Management Area (RKY) in Louisiana. Age and growth rates of top predators such as gars (Lepisosteidae) at these sites may serve as indicators of ecosystem health due to their high trophic position and frequent reliance on floodplains for spawning. From June 2020-December 2021, 572 gars (Alligator Gar Atractosteus spatula, Longnose Gar Lepisosteus osseus, Shortnose Gar L. platostomus, Spotted Gar L. oculatus) were
captured at LL and RKY using gill nets and cast nets, with a subsample from each site retained
for analysis of life history, growth, and trophic ecology. Based on sagittal otoliths, several old
individuals were identified, including a 56-year-old Alligator Gar, 23-year-old Longnose Gar, 34-year-old Spotted Gar, and the oldest known Shortnose Gar, at 49 years. Trophic position (based on δ 15N) was highest in Alligator Gar (3.55 ± SE 0.16, n = 6), followed by Longnose Gar (3.21 ± 0.03, n = 76), Shortnose Gar (3.02 ± 0.02, n = 153), and Spotted Gar (2.92 ± 0.03, n =107). To investigate differences in growth of gars between Mississippi River floodplains and other ecosystems, Spotted Gar data from LL and RKY were combined into a Mississippi River floodplain group and then compared to Spotted Gar populations from the Atchafalaya River
Basin, Upper Barataria Estuary, and a Near-coastal Marsh. Analysis of variance (ANOVA, α =0.05) indicated that Spotted Gar trophic position and mean length at age of multiple age classes were significantly higher at Mississippi River floodplain sites compared to the Atchafalaya River iv Basin, Upper Barataria Estuary, and Near-coastal Marsh. Parameters from von Bertalanffy growth models also suggested that Mississippi River floodplain gars reach a larger maximum size than gars from other Louisiana populations, and ANCOVA (analysis of covariance) indicated Mississippi River floodplain Spotted Gars exhibited significantly higher growth rates. This study created a baseline of life history values for four gar species which can be compared to other systems. Although abundant in some areas of the United States, gar species have been extirpated or are imperiled in several parts of their range. This study’s age and growth models suggest that Mississippi River floodplains support faster growth and larger size in gars and may be similarly beneficial to other species. These valuable freshwater ecosystems should be conserved, and other comparable sites should be restored.

 
Abstract
Spotted Gar Lepisosteus oculatus are a species of interest in genetics research as a translational link between teleost and tetrapod lineages, therefore, consistent access to Spotted Gar embryos and larvae are needed. Spotted Gar are good candidates for aquaculture due to size at maturity and stress tolerance but there are knowledge gaps in optimal feeding regime for larvae. Improved culturing techniques can increase access to Spotted Gar larvae for research. Additionally, Spotted Gar can be induced to spawn during the natural spawning season and out-of-season through hormone injection and temperature and photoperiod manipulation. To produce embryos and larvae for research, Spotted Gar broodstock were obtained from the Atchafalaya River Basin (ARB) that receives an annual flood pulse and the upper Barataria Estuary (UBE) that does not receive an annual flood pulse and may offer fewer resources than the ARB. Resource availability could impact female broodstock nutritional investment in eggs. Differences in environmental conditions could also drive variation in gene expression of Spotted Gar from different sites, which could impact research outcomes. Potential effects of broodstock collection site and timing of induced spawning on embryos and larvae, and optimal live prey items for cultured larval gar were explored.
Larvae from both basins and spawns were offered three zooplankton feeding regimes in triplicate, Moina only, Artemia only and both Artemia and Moina. A starvation study was also conducted to explore larvae survival without exogenous feed. A subsample of 10 larvae were randomly selected every three days for 18 days and total length (mm), wet weight (mg), body condition and relative lipid (mg/mL) and protein (μg/mL) content were measured. Mortalities were monitored and recorded daily and cannibalism rate was calculated at the end of each feeding trial.
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Total number of eggs spawned per gram of female and embryo size were similar between basins but higher in the in-season spawn than the out-of-season spawn. Prey items did not affect growth, condition or survival, but results may have been complicated by Moina availability. Out-of-season larvae grew larger than in-season larvae, but lipid and protein content was similar. Similar quality embryos and larvae based on growth, condition and survival were produced from the ARB and the UBE regardless of feeding treatment or season, therefore, larval quality was not affected by broodstock source. Out-of-season embryos and larvae were similar to in-season embryos and larvae, but a longer acclimation period for out-of-season spawns may increase total embryo and larvae yield. Future studies should further explore the use of Moina as a food source to culture larval Spotted Gar by analyzing fatty acid content to understand nutritional effects.

 
Abstract
Louisiana has lost roughly 25% of its coastal land since 1932 and is vulnerable to continued coastal land loss from anthropogenic activities and disasters, both human and natural. Prior to leveeing, the Mississippi River created millions of hectares of productive estuary habitats that supports 80% of the Louisiana economy and 60% of national commercial fisheries. Marsh terracing is used to enhance open water habitat for aquatic species. Marsh terraces have a high edge to area ratio with an extended littoral zone potentially creating high quality nursery grounds, but this habitat had yet to be assessed. I assessed the temporal and spatial use of newly created marsh terrace habitat and existing marsh habitat by larval and juvenile fish in Chauvin, Louisiana using quatrefoil light traps deployed every other week from April to September 2019 and March to September 2020. In 2019, the larval and juvenile fish assemblages were different in the terrace habitat compared to marsh habitat (P = 0.0019). In 2020, the assemblages were similar between the terrace habitat and marsh habitat (P = 0.4589). Habitat characteristics were also measured at the time of light trap deployment. The marsh terraces were planted in January 2019 and the vegetation was similar to the existing marsh within one year and remained similar in 2020 (P = 0.2420). Water temperature (°C), dissolved oxygen (mg/L), and salinity (ppt) were similar between habitat types for the duration of the study 2019 (P = 0.5915) and 2020 (P =0.4689). However, there was a difference in mean salinity at the marsh (P = 0.0042) and terraces (P = 0.0033) between years. Overall, my results indicated that marsh terraces produced nursery grounds that were similar to natural marsh.

 
Abstract
Stock assessments are vital in fisheries management to monitor past and current status on population size and structure and the potential responses of the fishery to future management decisions. However, there have not been extensive stock assessments for crayfish in the Atchafalaya River Basin (ARB). Crayfish stock assessments in the ARB have been difficult due to the lack of population data and reporting from harvesters and the enormous spatial scale of the ARB. The purpose of this research is to obtain a stock assessment for crayfish in the eastern ARB (east of the Atchafalaya River) by partnering with a local crayfish processor that purchases crayfish from harvesters throughout the eastern ARB. Crayfish harvest data was collected from March to August 2018 and January to July 2019 from harvesters, and included the number of traps fished, total weight of crayfish collected, and ARB spatial zone where crayfish were harvested (upper, middle, lower). Crayfish population characteristics (species, sex, carapace length, and male reproductive form) were examined weekly from three sub-samples of at least 400 individuals from different harvesters in each ARB zone (1,200 crayfish per week in each zone) from March to July 2018 and February to July 2019. Additionally, a minimum of 100 female Procambarus clarkii were collected monthly from three different harvesters in each ARB zone (900/month, 300/zone) to determine ovarian maturation stage and maturation index for each stage. The diameter of 20 oocytes per crayfish was measured in 10 female P. clarkii for ovarian maturation stages I-III and in three females in stage IV. In 2018, the lower zone had a significantly lower mean weight of crayfish per trap compared to the middle and upper zones (F2,998 = 12.93, P < 0.001) and P. clarkii in the upper zone had a smaller mean carapace length compared to individuals from the middle and lower zones (F2,52006 = 857.80, P <
iv0.001). The atypical, large ARB flood pulse in 2019 likely contributed to the observed reduced mean crayfish harvest (F1,1596 = 40.68, P < 0.001) and mean P. clarkii carapace length (F1,79803 = 4972.39, P < 0.001) observed compared to 2018. Throughout the 2018 and 2019 crayfish seasons, sexually immature ovarian maturation indices (stages 0-I) were highest from February to April, and sexually mature indices (stages II-IV) increased after May. Furthermore, mean P. clarkii oocyte diameter was significantly larger (F3,656 = 153.43, P < 0.001) for each increasing ovarian maturation stage. The results from this research will provide novel, high-quality fisheries-dependent data for the stock assessment of the eastern ARB crayfish fishery and provide baseline data for resource managers and future management decisions on the crayfish fishery.

 
Abstract
Coastal ridges are linear upland features in the coastal landscape that provide an abundance of ecosystem services. However, quantitative assessments of the ecological characteristics and processes of these habitats are limited. Little is known regarding either trajectories of terrestrial vegetation succession for restored coastal ridges, or the role of abiotic factors in structuring vegetation community composition in these habitats. The resolution of these knowledge gaps will enable ridge restoration projects to proceed in a more informed fashion, increasing the likelihood of success for future restoration projects along Louisiana’s coast. Terrestrial vegetation community composition and growth responses were studied using four nested ridge plots at ten sites within the Barataria-Terrebonne National Estuary System of varied hydrogeomorphic setting, landform age, and site history from June 2022 to September 2023. All live trees within replicates with a diameter at breast height (DBH) greater than 5 cm were identified and tagged with numbered aluminum tags. Soil core samples, 5-cm in diameter, were taken to a depth of 15 cm and analyzed for relevant soil metrics, including carbon content. High resolution elevation surveys were performed using Real-Time Kinematic (RTK) methods across the width of each replicate and at the base of individually tagged trees. Avian surveys that collected species sightings, calls, and observed behaviors, were conducted monthly from January 2023 to October 2023 by walking the length of the four maritime ridge sites. Trail cameras were also installed at these sites to record general biota presence and activity. Notable patterns were detected in various ecological characteristics and processes across the terrestrial habitats of coastal ridge types, settings, and ages. Importantly, reference (natural) ridges, restored and managed ridges, and spoil banks did not differ in either woody or understory vegetation community composition. Further, Quercus virginiana and Ilex vomitoria were noted
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as occurring across a wide range of ridge hydrogeomorphic settings and elevations within ridge settings, highlighting their importance in these habitats and desirability as a target species for restoration. Overall community composition of both woody forest species and understory composition demonstrated gradients with site age and soil salinity concentration. For example, younger, more coastal sites had a higher presence of shrub species Iva frutescens and Baccharis halimifolia. Older, natural forests had larger individuals but less sapling abundance. Terrestrial carbon stock in woody forest species also exhibited a discernible pattern with age. Key soil properties (e.g., bulk density, moisture content, etc.) fell within expected ranges for healthy coastal habitat in Louisiana, and displayed expected trends in extractable salinity consistent with distance from maritime influence. Surveys of avifauna occurrence suggests that the restored BTNEP ridge at Port Fourchon is successfully providing neo-tropical migratory song-bird habitat.

 
Abstract
The Rufa Red Knot (Calidris canutus rufa) is a shorebird with one of the longest migrations in the animal kingdom, therefore adequate prey abundance along their migration paths is necessary for success and survival. In the early 2000s, overfishing of prey led to Rufa Red Knot population decline and they were subsequently listed as federally threatened in the United States and endangered in Canada. Although considered primarily molluscivorous, in January 2022 I observed a Rufa Red Knot catch and eat a fish on the Chandeleur Islands, Louisiana, suggesting that their diets may be more diverse than previously thought. The purpose of this study was to characterize Rufa Red Knot diet using fecal metabarcoding. Rufa Red Knot fecal samples were collected from Grand Isle and the Chandeleur Islands. DNA was extracted, amplified, and sequenced from scat to identify invertebrates and fish. DNA was amplified with MiFish and 18S rRNA primers and sequenced on the Illumina MiSeq® platform. Sequences were assigned to a phyletic group, or species when possible, using a curated fish database of publicly available sequences and the BLASTn database. We detected two species of fish: Gulf Menhaden (Brevoortia patronus) and White Hake (Urophycis tenuis), and orders within mollusks, arthropods, annelids, and insects. To validate BLASTn results of fish and veneroida, pairwise MUSCLE alignments were performed in Geneious® 2023.0.4 to identify nucleotide differences between fecal sample sequences and known sequences from GenBank. The Rufa Red Knot fecal sample sequences showed one nucleotide difference from the known Gulf Menhaden sequence (DQ912033.1), but showed no nucleotide differences between the Rufa Red Knot fecal sample sequence and White Hake sequence (MT103927.1). Alpha diversity of Rufa Red Knot diet was not statistically different between sites (F1,56 = 5.823, P = 0.206) or between years at Grand Isle (F1, 38 = 0.428, P = 0.517). However, alpha diversity was higher in 2022 when both sites were included in the analysis (F1,56 = 5.823, P = 0.0191). Likewise, community diversity iv was statistically different between the Chandeleur Islands in 2022 and Grand Isle 2022 (P = 0.022) and between years at Grand Isle in 2021 and 2022 (P = 0.041). Our results confirm Rufa Red Knots primarily consume mollusks, but they do have some diversity in their diet. They exhibit opportunistic feeding habits and may choose alternative prey items such as fish and arthropods in scenarios where mollusks are not as abundant or there is a more efficient food source available. These data suggest that management decisions may need to include conservation of not only mollusks, but also fish and arthropods for Rufa Red Knots at their various stopover and winter sites, thereby allowing a higher probability of Rufa Red Knot migration success and survival.

 
Abstract
Recent studies have found microplastic (100nm-500nm) and nanoplastic (<100nm) particles to be ubiquitous contaminants detectable in virtually all habitat types. Microplastic presence and pollution reduction in freshwater systems is an emerging field of study due to recent evidence of impacts on organismal and ecosystem function. However, little research has been performed understand the interactions of vegetation with microplastics. Two mesocosm studies were performed to assess the interactions of microplastics with wetland macrophyte surficial tissues and to determine if aqueous microplastic contamination may be diminished through this mechanism. HDPE microplastics of small and large size classes, 43-250µm and 250-500µm respectively, were applied to experimental units containing either an emergent macrophyte, Panicum hemitomon, or no vegetation and compared to determine if vegetative tissues removed microplastics from surrounding surface waters. Experimental units containing Panicum hemitomon had significantly higher surface water microplastic abundance than experimental units with no wetland vegetation. However, microplastic abundance was significantly lower on vegetative tissues than in surface water of experimental units containing Panicum hemitomon. The presence of emergent vegetation may have acted to maintain concentrations of microplastics in surface waters by acting as weakly binding temporary points of attachment that allowed for cyclic series of adhesion and dislodging events. Further, 43-250µm sized microplastics were significantly more abundant in the experimental units than 250-500µm sized microplastics. Movement of water and air within the units may have more intensely affected the large microplastics with greater available surface area than small microplastics. Stomatal conductance, net CO2 assimilation, cumulative stem height, and biomass of Panicum hemitomon were measured over the three-month study duration to determine effects of microplastic exposure on growth and photosynthetic productivity. Stomatal conductance and net CO2 assimilation of Panicum hemitomon, Typha latifolia, Sagittaria latifolia, and Juncus effusus were also monitored during a 24-hour period of high microplastic concentration exposure and consecutive recovery period to determine if microplastics influenced photosynthetic characteristics. Plant growth and photosynthetic response were not significantly influenced by exposure of aboveground tissues to aqueous microplastics in either mesocosm study. No evidence of stomatal blockage was observed; therefore, microplastics of either size class may have been too large to remain in place along tissues to block stomata of experimental species. Additionally, chemical interactions that facilitate leaching of toxic compounds that can occur in microplastics do not appear to have occurred in these studies. This research has enhanced processing protocols for isolating and quantifying microplastics in vegetation studies. By providing a mechanistic understanding of vegetation surface-microplastic interactions, this study informs management strategies and enables future studies to refine nature-based microplastic abatement strategies.