Biology Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2749
Browse
12 results
Search Results
Item USING CALCEIN, A FLUOROCHROME CHEMICAL TAG, TO MARK SHELLS OF THE EASTERN OYSTER, CRASSOSTREA VIRGINICA, AND TO VALIDATE DIRECT SETTING OF OYSTER LARVAE(2021) Spires, Jason Eugene; North, Elizabeth W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Effective management of fisheries necessitates the advent and use of tools to monitor wild and introduced species. Tools currently available for marking shells of eastern oysters (Crassostrea virginica) predominantly rely on the physical handling of individual organisms and do not lend themselves to labeling large numbers of individuals with a durable tag. To test and apply an effective mass-marking tool for C. virginica, this research focused on 1) determining the efficacy of chemical labeling of multiple life stages of C. virginica using calcein, a fluorochrome dye, and assessing the potential impacts on survival and growth, and 2) identifying if the larval marking method could be used to validate the direct setting method of oyster stock supplementation that involved releasing larvae onto suitable habitat in situ. To investigate objective 1, multiple life stages of C. virginica were exposed to calcein immersion baths and tracked over time in laboratory experiments. Objective 2 was investigated through an applied field experiment that released calcein-tagged larvae onto constructed artificial reefs that were recovered and assessed for the presence of tagged juveniles. Results from labeling all life stages indicate that C. virginica readily incorporate calcein into shells with minor effects on settlement, growth, and survivorship at concentrations of 25 and 50 mg l-1 for larvae and 250 mg l-1 for juveniles and adults. These marks could be seen without sacrificing individuals, were visible on the shells of juveniles for at least four years, and were retained on the shells of pediveliger larvae for four weeks post metamorphosis. Calcein had little to no effect on the survival of most juveniles and adults and had no effect on the settlement rates of larvae. Field deployments of marked larvae on artificial reefs in the Tred Avon River showed that marked larvae were recovered in high concentrations at release sites, indicating that ‘direct setting’ of pediveligers onto shell bags in situ is possible without enclosures. This is the first known successful test of direct setting of C. virginica pediveliger larvae in situ that was verified with chemical mark and recapture methods. These findings have wide application for supporting C. virginica research, restoration efforts, and industries: these techniques could be used to strengthen comparative growth studies, validate larval transport models, evaluate stock enhancement activities, support law enforcement efforts, and enable testing of alternative setting strategies.Item BAHAMIAN OOLITIC ARAGONITE SAND IMPACT ON WATER QUALITY AND MITIGATION OF PHOSPHATE AND PHOSPHORUS REMOVAL AND RECOVERY IN RECIRCULATION AQUACULTURE SYSTEMS(2021) Rodgers, Steven R; Place, Allen R; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recirculating aquaculture systems (RAS) require management of water conditions to ensure animal health and limit nutrient discharges. Oolitic aragonite sand (OAS) forms from whiting events off the coast of the Bahamian Islands is a sustainable, renewable and effective in controlling water quality. Cyanobacteria mediate the precipitation of aragonite by capturing CO2, internally forming CO32-, which reacts with Ca2+ in seawater forming CaCO3 precipitations. Studies in freshwater, brackish and marine waters maintained stable pH and alkalinities. Initially, OAS removed phosphate rapidly, slowing afterwards. The OAS removed phosphate at rates of 716, 705 and 215 mg PO4/ kg OAS for freshwater, brackish and marine water, respectively. A system with daily P additions showed a removal capacity of 77.8 mg P /kg OAS. Treatment of phosphorus exposed OAS with 1.0% and 2.0% citric acid solutions show phosphate removals ranging from 17.3% to 93.5%. The citric acid increases the OAS surface area 1.66 times to 4.628 m2/g OAS, confirmed by SEM. Microbiome analysis show similar bacterial phyla exist on the naïve OAS and the OAS used in different salinities. Under anaerobic conditions, the control of system conditions were favorable for denitrification and anammox processes to occur. In freshwater, a loss of 215.8 gram of nitrogen (a loss of 90.5%) of the added nitrogen to the system occurred. In marine conditions, a loss of 253.04 g nitrogen, representing an 87.6% loss, occurred. Microbiome analysis identified phyla known to function as denitrifiers, though lacking known phyla for anammox bacteria. Losses of nitrogen in both salinities is likely due to denitrification, as oppose to anammox. OAS in RAS holding Eastern and Pacific oysters, showed dissimilar responses. The water quality remained in acceptable ranges for oyster growth. The survival in Eastern oysters (≥80%) contrasted with the Pacific oysters (≤56%). Weight increases occurred only with the Eastern oysters. Both species shows increases in shell length, width and height, but unchanged or decreases in weight. Reduced somatic growth and limited shell development occurred, perhaps due stresses from nitrogen spikes in the systems. OAS shows no positive advantage with oyster growth.Item Effects of Salinity on Settlement and Metamorphosis of the Eastern Oyster (Crassostrea virginica)(2016) Priester, Anna Priester; Meritt, Donald W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The eastern oyster (Crassostrea virginica) is a euryhaline species known for its historic populations, valuable fishery, and ecological importance. One of the most critical periods in the oyster’s life cycle is its transition from a free-swimming pelagic larva into its sessile benthic form. Despite the importance of this transition, which includes attachment to a substrate (settlement) and metamorphosis into the juvenile, our understanding of salinity tolerance during these processes is limited. This study was designed to quantify the effects of salinity on settlement and metamorphosis and to determine if those effects were influenced by the salinity in which the larvae were reared. Multiple cohorts of pediveliger larvae from hatcheries grown in Low (10), Medium (15-16.5) and High (22-27.5) salinities were allowed four days to settle in twelve salinity treatments ranging from 5 to 35. A set of additional experiments was extended to 14 days to investigate if the settlers were also able to complete metamorphosis and demonstrate juvenile growth within the same range of salinities. Settlement consistently occurred all tested salinities (5-35), indicating that pediveliger larvae can adapt to a broader salinity range than described in previous research. Highest settlement rates were achieved in treatment salinities between 11 and 30 for all three larval groups. Settlement performance outside that optimal range was highest for the larvae group reared in salinities closest to those extremes. Settlers from the 14-day experiments demonstrated metamorphosis and high post-settlement survivorship in all salinity treatments, but juvenile growth rates were reduced in salinities less than 9 and above 30. This highly repeated study reveals the impressive capacity for pediveliger larvae to tolerate a wide range of salinities and has direct implications for oyster aquaculture and our understanding of natural recruitment.Item INTEGRATING AUTOMATED IMAGING AND A NOVEL IDENTIFICATION TECHNIQUE TO ESTIMATE MORTALITY AND IDENTIFY FACTORS THAT INFLUENCE THE VERTICAL DISTRIBUTION OF CRASSOSTREA VIRGINICA LARVAE(2015) Goodwin, Jacob; North, Elizabeth; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Understanding the population dynamics and complete life cycle of bivalves is important for effectively manage them. Most of the literature and research to date has focused on juvenile and adult bivalves, much less is known about larvae. The larval stage of the bivalve life cycle has been difficult to study due to the lack of a rapid automated approach for identifying species. However, a new technique, called ShellBi, has emerged that utilizes color patterns on the larval shell under polarized light to identify bivalve larvae. The objective of this chapter was to review the scientific basis for ShellBi and to apply it to bivalve larvae in Choptank River with the goal of distinguishing C. virginica from seven other species that spawn at the same time. A digital camera and polarized light microscope were used to capture images of the shells of bivalve larvae under standard and cross-polarized light. Images of C. virginica were distinguishable from other species based on these patterns, especially at later stages of development. These images could serve as a visual guide to identify C. virginica collected from the Choptank River and other tributaries with similar species in Chesapeake Bay.Item THE EXCHANGE OF EASTERN OYSTER (CRASSOSTREA VIRGINICA) LARVAE BETWEEN SUBPOPULATIONS IN THE CHOPTANK AND LITTLE CHOPTANK RIVERS: MODEL SIMULATIONS, THE INFLUENCE OF SALINITY, AND IMPLICATIONS FOR RESTORATION(2015) Spires, Jason Eugene; North, Elizabeth; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)With limited funds available for restoration and management, information is needed that would enhance the objectives of restoration of the eastern oyster (Crassostrea virginica) in Chesapeake Bay. One challenge with choosing locations for C. virginica restoration is lack of information regarding larval exchange, which helps determine whether the reefs will be self-sustaining and/or enhance nearby populations. The goal of this research was to estimate the larval exchange between subpopulations within the Choptank and Little Choptank Rivers (Maryland, USA) and to determine the influence of low salinity on these patterns in connectivity. To this end, the Lagrangian TRANSport model (LTRANS) was coupled with a Regional Ocean Modeling System hydrodynamic model of Choptank River (ChopROMS) and applied to predict the exchange of simulated C. virginica larvae between 596 reefs within the system. Model results indicated that there is a high degree of connectivity among the subpopulations in this system. Most simulated larvae were transported down river (rather than upriver). Reefs in upper portions of the Choptank River and its tributaries were in a position to produce the most larvae which encountered suitable habitat, whereas those in the lower Choptank River received the most simulated larvae. In addition, salinity-induced mortality of larvae substantially decreased transport success and self-recruitment, and changed patterns in reef-specific transport success throughout the estuary. Model results provide region-specific information that could be used to support restoration efforts in areas with low salinities like the Choptank River.Item The Pursuit of a Sustainable Coastal Fishery: Comparisons of the Oyster Fishery in Chesapeake Bay and Ariake Sea(2012) Ishikawa, Momoko; Kennedy, Victor S; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A coastal fishery brings high productivity and economic profit while supporting cultural norms. However, it also causes environmental degradation and political conflicts, which sometimes collapse a fishery. With the current global shift from capture fisheries to aquaculture, appropriate management is required for social and environmental sustainability. To identify essential factors in coastal fishery management, I compared the oyster industries in Chesapeake Bay (USA) and in Ariake Sea (Japan) from political, environmental, and cultural perspectives, by field observations, interviews, and literature research. Despite their different historical backgrounds, the two regions have lost most of the oyster resource due mainly to 1) failure of environmental management, 2) environmental degradation and 3) resistance of the fishing communities to necessary changes in fishing methods and aquaculture. Based on these lessons, I propose that a coastal fishery management plan should include environmental management, development of government-initiated aquaculture, understanding cultural backgrounds, and cooperation among science, industry and politics as essential factors.Item Sex, Dispersal, and Deep Divergence: the Population Genetics of the Protistan Parasite Perkinsus marinus(2010) Thompson, Peter Christian; Hare, Matthew P; Rosenthal, Benjamin M; Behavior, Ecology, Evolution and Systematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The protistan parasite Perkinsus marinus causes Dermo disease in the eastern oyster, Crassostrea virginica. This parasite causes reduced growth and fecundity in its ecologically and economically important host, and as such has become a focal point for shellfish research. Though much is known regarding the seasonal dynamics and interactions between host and parasite, little research has focused on the basic biology of this parasite. In the research presented here, I used population genetic approaches to investigate the reproduction, dispersal, and origins of extant populations of P. marinus. First, I determined the extent of clonality in P. marinus populations. Repeated sampling of the same multilocus genotypes and extensive multilocus linkage disequilibrium indicated that clonal reproduction is prevalent. However, genotypic diversity was great and recombination occurred between genetic loci, supporting sexual reproduction as an important source of new genetic variation in P. marinus. An interesting consequence of sexual reproduction is that genotypic correlations may be maintained through inbreeding when sex occurs. Next, I investigated the genetic connectivity among locations. Clustering analyses revealed that local geographic samples are collections of independent clonal lineages rather than freely interbreeding populations. Some lineages were widespread while others were found at high frequencies only in specific locations indicating that P. marinus has a high capacity for dispersal, but local conditions may determine the success of certain lineages. Finally, I examined an interesting pattern of di-allelism observed in P. marinus DNA sequences. Two allelic classes were discovered at six out of seven nuclear loci where large divergences indicated the alleles had been independent for possibly millions of years. Balancing selection may be responsible for the retention of ancient diversity in this parasite, but it seems more likely that a recent hybridization event has occurred between two formerly allopatric lineages. These results underscore risks in the anthropogenic movement of protistan parasites as there may be no reproductive barriers between ancient lineages. Resulting hybrids could result in increased parasite virulence with increased disease in host populations.Item THE DIVALENT CATION TRANSPORTER NRAMP IN PARASITE PERKINSUS MARINUS: GENOMIC, MOLECULAR, STRUCTURAL, FUNCTIONAL AND EVOLUTIONARY ASPECTS(2010) Lin, Zhuoer; Vasta, Gerardo R; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Perkinsus marinus, the causative agent of Dermo disease in eastern oyster Crassostrea virginica has been a great hurdle for oyster population restoration. Iron was shown to be an essential element for P. marinus growth and virulence, but iron uptake pathways have not been elucidated. Natural Resistance-associated Macrophage Protein (Nramp), an iron transporter, was considered to be a potential virulence factor in intracellular pathogens. One Nramp homolog (PmNramp1) was reported in P. marinus previously. Two other PmNramp isotypes (PmNramp2 and PmNramp3) were identified through genome mining followed by molecular characterization. The three PmNramp isotypes with distinct gene structures were transcribed in parasite trophozoites cultured in defined medium. Transcripts of a number of P. marinus genes, including PmNramp isotypes, superoxide dismutases (PmSOD), ascorbate peroxidase (PmAPX) and heat shock proteins (PmHSP70 and PmHSP90) were trans-spliced with a trans-splicing leader (SL) highly similar to dinoflagellate SL. No change in transcription level of those genes was detected by real-time quantitative reverse transcription PCR (qRT-PCR), under iron/manganese overload, iron depletion and host hemolymph exposure, indicating a constitutive polycistronic transcription in the parasite. Functional study by yeast complementation assays suggested iron uptake activity by PmNramp1. Prediction of PmNramp1 topology by homologous modeling indicated that PmNramp1 was an integral protein with 12 transmembrane segments (TMS). The central position of the Nramp-specific triplets Asp-Pro-Gly (TMS1) and Met-Pro-His (TMS6) in a three-dimensional (3D) arrangement formed with TMS3 and TMS8 provided the mechanistic basis for iron acquisition via PmNramp1. Site-directed mutagenesis of the residues on the triplets in PmNramp1 caused the lost of complementation activity as iron transporter in yeast. A chimeric protein with PmNramp1 N- and C-termini but PmNramp3 core structure from TMS1 to TMS12 complemented yeast growth, suggesting PmNramp3 an iron transporter. Phylogeny data implied that all the three PmNramp isotypes were archetype Nramp. Protein sequence divergence among PmNramp isotypes was not related to diversification of critical functional elements, which remained constrained by purifying selection. This result was consistent with the function of both PmNramp1 and PmNramp3 as iron transporters in yeast, despite their different evolutionary rate and substitution patterns. Subcellular localization of PmNramp isotypes in P. marinus trophozoites are in progress. PmNramp3 was shown to localize on cell peripheral when the parasite proliferates by binary fission. The data were consistent with the previous observation that iron is important for P. marinus growth. As the first functional study of Nramp homolog in protozoan parasites, the work in the dissertation may serve as the reference for research in other protozoan Nramp and iron transporters.Item RELATIONSHIPS BETWEEN LARVAL MORPHOMETRICS AND SETTING EFFICIENCY IN THE EASTERN OYSTER, CRASSOSTREA VIRGINICA(2009) Vlahovich, Emily Ann; Meritt, Donald W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In oyster hatcheries, the decision to move larvae from rearing tanks to setting tanks is based on physical and behavioral characteristics. These criteria can suggest conflicting action and a more reliable method may result in higher spat production. I observed hatchery reared Crassostrea virginica larvae, beginning with larvae retained on a 200 µm sieve. Aliquots of larvae were measured or placed in a setting vessel, and the remaining were returned to the culture cone daily. Each day had an associated setting efficiency, loss, and set of larval morphometrics, including shell height and length and eyespot diameter. Day was most strongly correlated with setting efficiency. Eyespot diameter was moderately correlated with setting efficiency, and shell morphometrics were weakly correlated with setting efficiency. I estimated daily spat production, which peaked on day 2. These results suggest spat production may be increased by altering current hatchery methods to consider eyespot diameter or days past retention on a 200 µm sieve when deciding to place larvae in setting tanks.Item A von Bertalanffy Based Model for the Estimation of Oyster (Crassostrea virginica) Growth on Restored Oyster Reefs in Chesapeake Bay(2008-02-21) Liddel, Michael Keith; Paynter, Kennedy T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A model to estimate the mean monthly growth of Crassostrea virginica oysters in Chesapeake Bay was developed. This model is based on the classic von Bertalanffy growth function, however the growth constant is changed every monthly timestep in response to short term changes in temperature and salinity. Using a dynamically varying growth constant allows the model to capture seasonal oscillations in growth, and growth responses to changing environmental conditions that previous applications of the von Bertalanffy model do not capture. This model is further expanded to include an estimation of Perkinsus marinus impacts on growth rates as well as estimations of ecosystem services provided by a restored oyster bar over time. The model was validated by comparing growth estimates from the model to oyster shell height observations from a variety of restoration sites in the upper Chesapeake Bay. Without using the P. marinus impact on growth, the model consistently overestimates mean oyster growth. However, when P. marinus effects are included in the model, the model estimates match the observed mean shell height closely for at least the first 3 years of growth. The estimates of ecosystem services suggested by this model imply that even with high levels of mortality on an oyster reef, the ecosystem services provided by that reef can still be maintained by growth for several years. Because larger oyster filter more water than smaller ones, larger oysters contribute more to the filtration and nutrient removal ecosystem services of the reef. Therefore a reef with an abundance of larger oysters will provide better filtration and nutrient removal. This implies that if an oyster restoration project is trying to improve water quality through oyster filtration, it is important to maintain the larger older oysters on the reef.