UMD Theses and Dissertations
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Item DETERMINING FEEDING RATES IN EASTERN OYSTERS (Crassostrea virginica) USING NATURAL SESTON FLOW- THROUGH SYSTEM(2023) Wiltsee, Laura E.; Gray, Matthew W; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Bivalves are prized for the ecosystem services they provide. The removal of particles from the water column through filter feeding and resulting water quality benefits, known as the biofiltration services, of bivalves have been studied for over a century. This has created a wealth of knowledge around the mechanistic drivers of bivalve feeding activity. Recently, Chesapeake Bay ecosystem-wide models have begun incorporating Eastern Oyster (Crassostrea virginica) biofiltration. Acute feeding variability is critically important when estimating oyster biofiltration services at ecosystem scale. Typically, natural seston clearance rate studies last a limited timeframe, with a focus on specific environmental events such as an increase in temperature, drop in salinity, or a tidal cycle.To capture the highly variable filter feeding rate of bivalves, such as the Eastern Oyster, studies have used highly controlled laboratory conditions, with single environmental variable modification. These studies often use indirect methods for estimating clearance rates that commonly lack high-resolution capability. Furthermore, these studies are labor intensive and time consuming, and as a result, few studies have monitored bivalve feeding activities over long periods to understand variation in activity or how these rates may change with seasonal shifts in conditions. These limitations have led to a shortage of knowledge around how clearance rates of oysters vary in response to ambient conditions over both short-term (hourly) and long-term (seasonal) time scales. This study leverages advances in semi-autonomous aquatic observing to track high- resolution, long-term feeding responses of bivalves to subtle variations in environmental conditions. Oyster ex situ clearance rates in the Choptank River (Maryland, USA) were estimated under flow-through conditions, and logged in real-time using fluorometers among replicate oysters over 5-day experiments for 9 months. The measured clearance rates from this system were compared to a mechanistic clearance rate model used by the Chesapeake Bay Program, which is used to estimate the role of oysters in controlling water quality in the Bay. Environmental data were evaluated to build a statistical and random forest model to predict how oyster clearance rates respond to prevailing environmental conditions. This monitoring system and resulting models enable a deeper understanding of feeding variability and how natural seston and environmental variability directly influence oyster physiology.Item PREDICTING THE SALINITY HISTORY OF OYSTERS IN DELAWARE BAY USING OBSERVING SYSTEMS DATA AND NONLINEAR REGRESSION(2022) HOWLADER, ARCHI; NORTH, ELIZABETH; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Salinity is a major environmental factor that influences the population dynamics of fish and shellfish along coasts and estuaries, yet methods for predicting the salinity history at specific sampling stations are not widely available. The specific aim of this research was to predict the history of salinity experienced by juvenile and adult oysters (Crassostrea virginica) collected at sampling stations in Delaware Bay as part of the Selection along Estuarine Gradients in Oysters (SEGO) project. To do so, empirical relationships were created to predict salinity at five oyster bed stations using observing systems data and then applied to construct indices of salinity exposure over an oyster’s lifetime. The desired accuracy was +/- 2 psu. Three independent sources of salinity data were used in conjunction with observing systems data to construct and validate the predictive relationships. Observing systems data from the USGS station at Reedy Island Jetty and continuous near-bottom measurements taken by the U.S. Army Corps of Engineers (ACOE) from 2012-2015 and 2018 were employed to fit nonlinear empirical models at each station. Haskin Shellfish Research Laboratory (Haskin) data were used to evaluate model fit, then ACOE data from 2018 (withheld from model fitting in the validation analysis) and SEGO data from 2021 were used to validate models. The best-fitting models for predicting salinity at the oyster bed stations given the salinity at Reedy Island Jetty were logarithmic in form. The root mean square error (RMSE) of the models ranged from 1.3 to 1.6 psu when model predictions were compared with Haskin data, 0.5 to 1.5 when compared with ACOE data, and 0.6 to 0.8 when compared with SEGO data. All of these models were within the desired accuracy range. Results demonstrate that observing systems data can be used for predicting salinity within +/- 2 psu at oyster bed stations within 39 km in upper Delaware Bay. When these models were applied to estimate low salinity exposure of 2-year-old oysters via the metric of consecutive days below 5 psu, the indices suggested that there could be as much as a 42-day difference in low salinity exposure for oysters at stations 31 km apart. This study helps further our understanding of the salt distribution in Delaware Bay as well as the effect of low-salinity stress on the life cycle and genetic differentiation of oysters. In addition, the approach of using observing systems data to predict salinity could be applied to advance understanding of salt distribution and the effect of low salinity exposure on living resources in other estuaries.Item The effect of aquaculture gear and tidal zone on the growth and shape of the oyster Crassostrea virginica during a “finishing period” in Chesapeake Bay.(2016) Thomas, Laura Landis; Plough, Louis V; Cornwell, Jeffrey C; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study investigated how aquaculture gear type and increased wave action influenced growth and shape of eastern oysters Crassostrea virginica during a “finishing” period in Chesapeake Bay. Oysters were deployed in three different gear treatments in the intertidal or upper water column: bottom cages, OysterGro™ floats, and rack and bag, and a bottom cage was also deployed in the subtidal zone as an industry control. Shell length(L), width(W), height(H), total weight and wet meat weight were measured each month from August to December 2015 and an index of shell shape (deviation of L-W-H from idealized 3-2-1 ratio) calculated. OysterGro™ floats produced the greatest increase in wet and total weight and the most ideal shaped oysters (lowest 3-2-1 ratio deviation). Overall, these results demonstrate the benefit of deploying oysters in higher wave action gear types such as the OysterGro™ and will increase the available data on gear performance in Chesapeake Bay.Item Influences of the biotic and structural components of Crassostrea virginica on the oyster reef community.(2015) Kesler, Karen Elizabeth; Paynter, Kennedy T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The hard, complex reef structure created by the eastern oyster, Crassostrea virginica, provides refuge and habitat that protects many organisms, allowing them to settle, survive, and spawn. In addition, oysters create copious amounts of biodeposits, which potentially serve as a basal nutrient resource for the reef ecosystem. I investigated the influence of oyster reef structure and oyster biodeposits on the reef community through a series of field experiments and mesocosm studies. Initially, the communities that colonized live oyster reefs were compared to communities that colonized empty oyster shell reefs, to evaluate the potential influence of live oysters that were actively feeding and creating biodeposits. Community assemblages on the two reef types were similar and no differences were seen with species level comparisons of abundance or biomass between the two treatments. The impact of oyster shell structure on energy transfer up the food chain from the basal resource of oyster biodeposits to the predator, Gobiosoma bosc, through the amphipod, Melita nitida was then investigated. Oyster shell structure effectively provided protection to amphipods, with reduction of predation impacts in high complexity habitats when a predator was present. Next, stable isotope signatures (d13C and d15N) of dominant reef species and basal resources, including oyster biodeposits, were measured seasonally to evaluate the major resource contributors to the reef. Overall, most carbon sources appeared to be pelagic in nature and an additional unidentified carbon source from outside of the oyster reef was incorporated into the food web. Finally, a d15N tracer study, utilizing biodeposits labeled with elevated d15N values, indicated that both Melita nitida and Neanthes succinea could incorporate Crassostrea virginica biodeposits and pass these nutrients to higher trophic levels. These studies suggested that oyster structure played a prominent role in defining the oyster reef community by providing habitat and protection for reef organisms. Mesocosm studies and isotopic analysis indicated that while some deposit feeders could consume oyster biodeposits, biodeposits were likely not a large component of their diet. Overall, these results suggest that structure was the dominant factor driving community organization on the reef, with minimal influence from oyster biodeposits.Item THE EFFECTS OF THE DIEL-CYCLING OF DISSOLVED OXYGEN AND pH ON THE EASTERN OYSTER, CRASSOSTREA VIRGINICA (GMELIN), CLEARANCE RATES AND HEMOLYMPH pH(2014) Clark, Virginia M; Breitburg, Denise L; Harris, Lora A; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Chronic hypoxia and hypercapnia affect Crassostrea virginica. Less is known about how the co-cycling of these stressors, as occurs in shallow waters worldwide, affects this filter feeder. I used laboratory experiments and age-specific models to test how diel-cycling hypoxia and hypercapnia affect algal clearance rates by C. virginica and C. virginica hemolymph pH. Clearance rates were reduced during periods of low dissolved oxygen, but older oysters compensated by clearing faster when DO returned to normoxia. Models indicated that this compensatory feeding may allow older oysters to avoid decreases in average summertime clearance rates. Low hemolymph pH has been linked to decreased immune function in marine invertebrates and low water pH decreases the hemolymph pH of oysters. My hemolymph experiment also showed that hemolymph pH decreased with decreasing water pH and indicated that oysters may begin to compensate for declining water pH at water pH values between 7.60 and 7.36.Item COMPARATIVE PHYSIOLOGICAL ECOLOGY OF THE EASTERN OYSTER, CRASSOSTREA VIRGINICA, AND THE ASIAN OYSTER, CRASSOSTREA ARIAKENSIS: AN INVESTIGATION INTO AEROBIC METABOLISM AND HYPOXIC ADAPTATIONS(2012) Lombardi, Sara Ann; Paynter, Kennedy T; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Eastern oyster, Crassostrea virginica, has a remarkable ability to withstand low oxygen conditions. However, the taxonomically and morphologically similar Asian oyster, Crassostrea ariakensis, died earlier than C. virginica during hypoxic exposure in multiple studies. My dissertation research sought to understand the physiological basis for this difference in tolerance. The aerobic metabolic rate of these species was assessed and a theoretical investigation into the importance of correctly standardizing metabolic rate by mass was conducted by using multiple techniques to analyze the respiration data. Crassostrea ariakensis juveniles exhibited higher mass-specific respiration rates than C. virginica , while there was no difference between adults. Further, the approach used to standardize mass vastly affected the results. When adult oysters were exposed to hypoxic water (oxygen concentration below 0.5mgL-1) for 24 hours, C. ariakensis gaped more frequently and wider than C. virginica and gaping was associated with acidification of the ambient water. When gaping was restricted by clamping, the longer an oyster was clamped the more acidic the hemolymph became in both species and a more acidic shift was observed in C. ariakensis. This research also investigated whether hypoxic-induced gaping was a behavioral or physiological response by exposing oysters to hypoxic, hypercapnic, and both hypoxic and hypercapnic environments and assessing metrics of adductor muscle contraction strength and speed. No significant difference was observed in the contraction strength (log10 transformed grams) between species, gas type, or the length of time exposed to the gas treatment. While there was no significant species effect on the speed of contraction (square root transformed seconds until peak contraction strength), oysters within the combined hypoxic and hypercapnic environment contracted more slowly than those in other treatments. When oysters were exposed to gas treatments for eight hours they exhibited the slowest rate of contraction, but there was no significant linear relationship between time exposed and time (square root seconds) to peak contraction strength. This research indicates different biochemical responses to hypoxia between closely related species which may assist in identifying mechanisms responsible for hypoxia tolerance and may contribute to restoration decisions.Item DEVELOPING SPATIALLY-EXPLICIT ASSESSMENT TOOLS FOR EASTERN OYSTER IN CHESAPEAKE BAY(2011) Livings, Maude Elizabeth; Wilberg, Michael J; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Decreasing abundance of the eastern oyster Crassostrea virginica in Chesapeake Bay is of concern because of its ecological, economic, and cultural importance. The objective of my study was to develop methods for conducting stock assessments of eastern oysters in Maryland waters of Chesapeake Bay that estimate abundance, recruitment, and fishing mortality at regional scales. First, I evaluated how spatial patterns in autocorrelation of recruitment and adult relativity density varied over time by fitting semivariogram models to survey data for each year. This information was then used to determine appropriate scales for my second objective which was to develop a stage-based model for the lower Potomac River using data from the Maryland Department of Natural Resources fall dredge survey and fishery data from the Potomac River Fisheries Commission. Estimated abundance declined to approximately 39% of that in 1990. The analyses will provide a platform for regional management of eastern oysters.Item NAKED GOBIES (GOBIOSOMA BOSC) AS INDICATORS OF OYSTER REEF RESTORATION SUCCESS(2009) Lederhouse, Terra Marie; Paynter, Kennedy T; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Naked gobies (Gobiosoma bosc) are the most abundant resident fish on oyster reefs in the Chesapeake Bay and serve as a critical trophic link between the benthic and pelagic communities. Their response to oyster restoration may therefore be a useful indicator of ecosystem functioning. Experiments were conducted from 2005-2006 in the Severn and Patuxent Rivers to determine the response of naked gobies to increasing availability of oyster substrate. Naked gobies and other resident macrofauna were collected from experimental oyster reefs, constructed using adult oysters of various densities, loose oyster shell, and ambient sediment. Naked goby abundance, length, dry weight, and biomass increased with the availability of oyster substrate and were positively correlated with the abundance of other resident macrofauna. Individual dry weight and biomass were greater on reefs with a high density of oysters than on control plots, and may therefore serve as important indicators of oyster reef habitat quality.Item Population genetics of the eastern oyster in Chesapeake Bay(2008) Rose, Colin G.; Hare, Matthew P; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The eastern oyster, Crassostrea virginica, plays an important role in the ecology of Chesapeake Bay. Its large population size, long larval dispersal stage and potential for high variance in reproductive success is representative of many marine invertebrates. Nevertheless, many important aspects of the oyster's biology remain unclear. I investigated how migration, natural selection, and effective population size have shaped the evolution of Chesapeake oysters. First, I examined aspects of genetic connectivity among oysters from rivers throughout the Bay. A correlation between geographic and genetic distance indicated that oyster larval dispersal tends to be local and that migration between Bay tributaries is rare over an ecological time scale. This result contributes to a growing body of literature indicating that larval dispersal is not passive. Next, I showed that a pattern of non-neutral mitochondrial evolution previously observed in different oyster populations also existed in Chesapeake Bay C. virginica. Tests of selection indicated that the pattern, in which there is an excess of high frequency and low frequency haplotypes and a deficit of intermediate frequency haplotypes, was the result of positive selection on the genome. Demographic explanations appear unlikely to account for the mitochondrial haplotype pattern because nuclear loci exhibited neutral patterns of sequence evolution. Estimates of effective population size were several orders of magnitude smaller than census size, indicating that there was variance in reproductive success (sweepstakes reproduction). Nevertheless sweepstakes reproduction was not so severe that individual cohorts of juvenile oysters exhibited reduced levels of variation compared to the adult population. Finally I evaluated the risks associated with a supplementation program in which hatchery-raised oysters bred for disease tolerance were released into wild oyster populations. The results indicated that following supplementation, the wild effective population size remained large despite the danger of severe genetic bottlenecks. Increased hatchery effective population is suggested to prevent future harm to the wild population.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.