The eastern oyster (Crassostrea virginica Gmelin 1791) has great ecological and economic importance but populations have declined, especially in Chesapeake Bay, to historically low numbers. Hatcheries strive to produce oysters with beneficial characteristics for supplementation and commercial purposes, both natural and stimulated mass spawning. Unequal contribution of parents in mass spawnings potentially can lead to high levels of inbreeding and a loss of beneficial characteristics in offspring. In this study, we determined microsatellite genotypes for parents (n^parents =24, 49, and 77 parents) and progeny (n=96 each) of three hatchery-produced families and used the data for parental assignment. We observed the presence of more than two alleles per locus for some offspring, yet because genetic analysis software only allows for a maximum of two alleles per locus, we chose the two alleles with the strongest signals. For the three parent “populations,” 71% of alleles had frequencies of <0.05 and observed heterozygosities were lower than expected by an average factor of 0.27. Inbreeding within the various parent populations was similar across the three families ranging from F^IS 0.26–0.43. In all three families, the offspring exhibited greater levels of genetic diversity and lower inbreeding levels than the parents (F^IS 0.14–0.21), and in some cases offspring exhibited alleles that were not present in the parents. Variance in the number of offspring produced per parent was observed for all families and in general, <10% of potential parents (generally 2-5 females and 1-3 males) produced >10% of the offspring. Reproductive success for spawning parents, N^b, determined by three methods, ranged from 0.07 to 0.27. As the number of parents per family increased, a higher proportion of parents failed to produce offspring. Across all three families, the average effective number of breeders was N^b = 7.1 and the level of reproductive success was inversely proportional to the number of potential parents. This finding implies that to maintain high levels of diversity and beneficial characteristics in the offspring (and to avoid the chance of unintentional inbreeding), hatcheries should perform more spawnings with fewer parents.

The lack of success in restoring oyster, Crassostrea virginica, populations to Chesapeake Bay and its tributaries has raised many questions about why many restoration efforts have failed. A number of studies have focused on the larval stage of oysters and considered the variables that impact oyster setting behavior in an effort to understand why oyster populations have not recovered. Studies that have examined setting surfaces suggest that biofilms promote oyster larval settlement; however, similar studies with barnacle larvae have found an inhibitory relationship. The present study utilized field-produced biofilms of different ages to determine if natural biofilms inhibit or promote setting of larval oysters. Several aspects of the biofilms where analyzed including biomass, chlorophyll a concentration, percent organic matter, bacterial cell counts, and bacterial community composition. Larval setting was found to increase as biomass and age of biofilm increased. No effects of chlorophyll a concentration, percent organic matter, bacterial cell counts, or bacterial community composition were detected. The predator Stylochus elipticus was observed to have a profound effect on newly set larvae. A new method for enumerating bacterial cells was explored to promote high throughput analysis of biofilm specimens. This method involves applying bacterial suspensions to bio-adhesive slides with subsequent staining and was compared to the standard method of enumeration on filters. The bio-adhesive slide procedure allowed processing of ten times more specimens per slide, resulted in lower background fuorescence, and higher bacterial counts than the standard filter method. The method promoted high throughput while yielding more accurate counts than filters when compared to dilution curves and was found to be useful for direct enumeration of bacteria in laboratory cultures, wastewater, sediments, and biofilms.

Invasive colonial tunicates pose substantial economic threat to the shellfish aquaculture industry, but their population dynamics and ecological impacts are highly variable and region-specific. This thesis contributes to our regional understanding of two such tunicates in Oregon. The first chapter explores the population dynamics of Didemnum vexillum, one of Oregon’s top 100 most dangerous invasive species, at an oyster farm. From May 2011 to 2016 the population fluctuated extensively, though did not exhibit any net growth over the study period. In the second chapter, I demonstrate that Botrylloides violaceus had no impact on the growth, condition, or organic composition of oysters and mussels grown in a simulation of longline aquaculture. Together, these studies paint a cautiously positive outlook for the shellfish aquaculture industry in Oregon. This thesis includes previously unpublished co-authored material.

The principal aims of this thesis were to examine whether there were hydraulic links between individual on-site wastewater systems in sandy soils at Salt Ash and the Tilgerry Creek estuary near Port Stephens, New South Wales, and whether the chemical and microbiological contaminants from on-site systems could reach surface and groundwaters, and possibly lead to impacts on estuarine oyster growing waters. The research outcomes are contained within the thesis and in four refereed papers presented at conferences, and which have been subsequently published, or are in press. Copies of each of these papers are contained within the thesis Appendices. The presence of faecal contamination from domestic systems in the estuary, and surface drains in particular, has been confirmed by work contained in this thesis. The potential level of risk to human health from the consumption of contaminated oysters is, however, regarded as very low, although an assessment of health risk using established microbial assessment models has not been undertaken / Doctor of Philosophy (PhD)

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Patrick M. Gaffney, School of Marine and Earth Studies. Includes bibliographical references.

Graduation date: 1953

The green porcelain crab, Petrolisthes armatus, has recently invaded oyster reefs of the South Atlantic Bight at mean densities of up to several thousand individuals m-². Despite the crab’s tremendous densities and wide-spread occurrence, its population dynamics, the reasons for its success, and its ecological impacts have remained unknown. We used field monitoring in two estuaries of coastal Georgia to assess spatial and temporal patterns of distribution, demographics, reproduction, and effects on native crabs. We used field and mesocosm experiments with constructed oyster reef communities of varying native species richness and adult porcelain crab additions to assess why the invader is successful and how it impacts native species and communities. We found P. armatus distributed throughout the estuaries, primarily in the lower regions and low intertidal. Sex ratios were 1:1 throughout the year. During warmer months mean densities ranged from 1,000-11,000 crabs m-², 20-90% of mature females were gravid, and numerous recruits were present. Despite decreases in density of 64->99% in the winter, populations rebounded in the spring. Maximum mean densities were 37 times the highest densities ever recorded and population fecundity exceeded that of the native range by an order of magnitude, but correlations did not show significant negative effects of P. armatus on native crabs. Field experiments suggested that invasion was successful due to tremendous recruitment overwhelming biotic resistance by native species richness or predation. The crab only needed structure to invade, but the presence of adult conspecifics significantly enhanced recruitment (i.e., intraspecific “invasional meltdown”). We documented several impacts on native biota, including the (1) suppression of oyster growth, benthic algal biomass, native crab recruitment, and native goby densities and the (2) enhancement of bivalve recruitment, macroalgal cover, and survivorship of oyster drills. We did not, though, see an effect on native taxonomic richness. The large direct and indirect effects of P. armatus on growth, survivorship, and recruitment of virtually all of the most common native species on oyster reefs in the short-term (4-12 weeks) and at relatively low experimental densities (750-1500 crabs m-²) imply considerable long-term consequences for a major hard-substrate habitat of the South Atlantic Bight.

Tapeng Bay is the second largest lagoon in Taiwan. The biological and ecological environments are an autotrophic system and are influenced by seasonal variability, terrestrial pollutant inputs and the exchange rates with seawater. There¡¦re intense oyster culture and fish farming activities in the bay before July, 2002. The oyster was the most important spineless member in the lagoon. They would filtrate microplankton and detritus; they would also excrete nutrient and consume dissolved oxygen. Therefore, oyster played a very crucial role in the Tapeng Bay. This study combines the biological responses of the oysters with the complicated interaction among microplankton, nutrient, detritus and dissolved oxygen to establish the relationship of dynamical mechanisms between variables by applying the system dynamics simulation software STELLA. Model results clearly reveal that the oysters are the main species of filtration. The factors which affect the biomass of oysters include microplankton concentration, temperature and individual mass; the connection between oysters and other biological variables is closely tied. The study has also shown that the removing of oysters may cause significant increases of plankton and detritus during the eutrophication condition. Although the simulated water quality variables show higher than those obtained from sampling experiments in the literatures, the trend corresponds well with the relative studies. Despite the fact that oysters excrete much nutrient and nutrient is mostly taken up by microplankton, the condition of nutrient limitation has never happened, which is in correspondence with the result. In the sensitivity analysis, the parameters of oyster filtration rate and the autotroph nitrogen to carbon ratio are important factors which have influence on oysters biomass, and the concentration of microplankton and ammonium. Oyster excretion rate and the proportion of oyster feces and pseudofeces also have significant influences on the concentration of ammonium. The oyster culture racks in the Bay have already been torn down, but the Bay is still eutrophic. This is a clear indication of the importance of the oysters in the lagoon. Properly culture some oysters in the area where exist high concentrations of microplankton or organic input. By applying the oyster abundant filtration, planktons and suspended solids, mostly detritus and organic matters, can probably be controlled and the water quality in the bay can thus be improved. Although the STELLA has its limitation on broader applications, the model developed by this study can be combined with the features of social or economic fields. A decision supporting system can be developed for the management of ecological environment policies.

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: Patrick M. Gaffney, College of Earth, Ocean, & Environment. Includes bibliographical references.

The quantification of population and mortality data for insect pests of apple is necessary if we are to gain fundamental insight in the dynamics of insect populations of the orchard ecosystem. The need to quantify has recently been emphasized (LeRoux, 1964a; 1964b) and the greater application, practical and scientific, or the quantitative results obtained for agricultural and forest insect pests has been demonstrated (LeRoux et al., 1963). [...]