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Thesis (Ph. D.)--University of Rhode Island, 2004. / Typescript. Includes bibliographical references (leaves 221-243).

Graduation date: 1981

The shallow, wave-swept sea floor off the central Oregon coast is used by 0-age flatfishes as a nursery ground. This dissertation is based on a series of projects designed to: 1) identify the dominant meiobenthic nematodes present in a coastal nursery area; 2) describe the important temporal and spatial scales of nematode variability at this site; 3) discuss the role of sediment disturbance in structuring nematode assemblages; and 4) relate seasonal and spatial differences in the distributions of meiobenthos to observed changes in the diet of flatfishes. The 19 numerically dominant nematode species found at the study site showed significant fluctuations in density over a 15 month period, yet their rank order based on abundance did not change. Four mechanisms capable of producing seasonal changes in nematode abundance without altering species proportions are discussed: winnowing from sediments, non-selective predation, seasonally variable food resources, and compensatory links between birth and death rates among species. Significant differences in the abundance of nematodes were found over horizontal distances of kilometers and centimeters. Sediment disturbance contributes to the generation of these spatial patterns. Over broad scales there were two distinct faunal groups associated with different water depths. The division between these assemblages was closely correlated with the threshold depth at which sediments are influenced by passing waves. On small scales (<0.25 m²), the distributions of the numerically dominant species varied seasonally. In the winter, frequent storm activity mixes the bottom sediments and randomly distributes the fauna over the sea floor. In the late spring and summer, physical disruption of sediments is minimal and biological factors, e.g., attraction between males and females, lead to aggregation. Food habits of juvenile English sole were a function of location of capture within the study area, season, and fish length. Diets of fish less than 35 mm SL varied greatly both between seasons in the same year and between years. Diets of English sole captured in trawls obtained at the same depth and different depths were similar in January 1979 but were highly variable in May 1979. These temporal and spatial differences in feeding are thought to be related to seasonal changes in the abundance and spatial distributions of benthic prey. / Graduation date: 1982

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Thesis (Ph. D.)--University of Rhode Island, 2004. / Typescript. Includes bibliographical references (leaves 162-175).

The effect of various concentrations of thiourea on the production of thyroid hormones was investigated in the starry flounder, Platichthys stellatus. Flounder were immersed in sea water solutions of thiourea in concentrations of 0.0001%, 0.0005%, 0.001% and 0.0025% for periods of 10 - 11 days and in concentrations 0.005%, 0.01%, 0.02% and 0.03% for as long as 74 days. After injections of tracer doses of radioiodine, extracts of the thyroid glands were subjected to autoradiochromatography. It was established that concentrations of thiourea ranging from 0.0025% - 0.03% completely inhibited the synthesis of the thyroid hormones throughout the course of the experiments. Although the synthesis of the thyroid hormones was abolished in flounder exposed to 0.0025% and higher concentrations of thiourea, flounder in some instances were able to synthesize moniodotyrosine and diiodotyrosine. The significance of this phenomenon is discussed in connection with biosynthesis of the thyroid hormones and the mechanism of antithyroid activity of thiourea. Measurement of the percentage uptake of the injected dose of radioiodine revealed that inhibited flounder consistently had lower values in the thyroid when compared to controls. / Science, Faculty of / Zoology, Department of / Graduate

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The acanthocephalan Echinorhynchus lageniformis Ekbaum, 1938, is a common intestinal parasite of the starry flounder, Platichthys stellatus (Pallas), of Yaquina Bay, Lincoln Co., Oregon. Three hundred and sixty-one flounders were examined and 146 (40.5 percent) were found to harbor infections of E. lageniformis. Cystacanths of E. lageniformis were found encysted in the body cavity of the starry flounder; this is probably the result of the fish feeding on larval infections not yet mature enough to attach to the intestinal mucosa. As the size of the flounder increased, the percent infection decreased. The smaller fish with the higher incidence of infection were found to be of the size range that ate amphipods, which may be the intermediate host, as the main part of their diet. The older fish do not feed on amphipods. A correlation could not be found between the sex of the starry flounder and the incidence and degree of parasitism. A peak of adult worms was found in April, 1966 - 198 mature females as compared to a low of 30 mature females in December, 1965. This indicates a seasonal periodicity in the E. lageniformis population of Yaquina Bay. Possible explanations for this seasonal occurrence were discussed. It is postulated that E. lageniformis lives in its final host for about a year. The one-year-old plus fish were found to have a high incidence of infection, whereas the two-year plus fish had a low incidence of infection. Twenty-six percent of the worms collected were males and 74 percent were females. Of the 146 infections, 74 were unisexual and 72 were mixed (containing both sexes). In April, 1966, the percent infection was the highest - when there were 20 mixed infections and two unisexual infections. This indicates that all the females have a good chance of being fertilized. The starry flounder intestine reacts to E. lageniformis at the point of attachment. It was observed that the larger the worm, the more severe the reaction. No crowding effects were observed in single species infections of E. lageniformis or in concurrent infections with trematodes. The shelled acanthor larva was found to have four enveloping membranes. Data indicates that when the proboscis reaches a certain length and width, it does not increase in size, although the neck and trunk of the worm do increase in size. / Graduation date: 1967

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