Hemigrapsus oregonensis and Hemigrapsus nudus, two beach crabs common on the Pacific Coast of North America, show considerable variation in numbers, and species dominance from place to place. To determine why this should be so, a number of experiments were performed, and observations made to determine what are the morphological, and physiological differences between the two species, and how the crabs would be affected by the different physical conditions prevailing in different places. In general, it appeared that H. nudus could not tolerate muddiness of the substrate, while H. oregonensis tended to be eliminated from clean areas by predators. The abundance of the crabs appears to be correlated with the amount of cover available. / Science, Faculty of / Zoology, Department of / Graduate

xi, 153 leaves : ill. Typescript. (Another copy on microfilm is located in Archives) Thesis (PhD.) -- University of Oregon Includes vita and abstract Bibliography: leaves 145-153 University of Oregon theses, Dept. of Biology, Ph.D., 1981

Typescript. Includes vita and abstract. Bibliography: Includes bibliographical references (leaves 45-47). / Rhithropanopeus harrisii is an introduced Atlantic crab in Coos Bay, Oregon. In Coos Bay, it occurs only in the uppermost estuary where salinities are seasonally low (<1 0/00). Rhithropanopeus occurs at higher salinities in its native range, and tolerates higher salinities in the laboratory. A native crab, Hemigrapsus oregoneos1s, occurs in the estuary, but not as far up into the oligohaline and freshwater zones as Rb1tbcopanopeus. In laboratory experiments, adult Hem1grapsus consume juvenile Rhithropanopeus. Hemjgrapsus is significantly more aggressive than Rhithropanopeus. The absence of juvenile Rhithropanopeus at field sites where both species occur suggests that field interactions may be occurring. Taken together, these results and observations suggest that there may be a dynamic zone in the estuary where the distribution of Rhithropanopeus is restricted by Heroigrapsus. Rhithropanopeus may find a refuge from Hemigrapsus in the oligohaline-freshwater Zones of the estuary, such that Hemigrapsus may be exerting selective pressure on the Rhithropanopeus population favoring freshwater adapted individuals.

Contaminants such as pharmaceuticals are of increasing concern due to their ubiquitous use and persistence in surface waters worldwide. Limited attention has been paid to the effects of pharmaceuticals on marine life, despite widespread detection of these contaminants in the marine environment. Of the existing studies, the majority assess the negative effects of pharmaceuticals over an exposure period of 30 days or less and focus on cellular and subcellular biomarkers. Longer studies are required to determine if chronic contaminant exposure poses risks to marine life at environmentally relevant concentrations. Also scarce in the literature is examination of whole organism effects to identify potential community-level consequences. Two long-term studies with the antidepressant pharmaceutical, fluoxetine (the active constituent in Prozac®) were conducted to determine whether nominal concentrations detected in estuarine and coastal environments affect organism health and interactions. First, we measured whole organism metrics in the California mussel, Mytilus californianus over a period of 107 days. Specifically, we measured algal clearance rates, growth, and condition indices for both reproductive and overall health. We found that fluoxetine negatively affects all measured characteristics, however many effects are mediated by length of exposure. Perhaps the most notable result was that mussels spiked with fluoxetine cleared less algae after 30 days of exposure. Reduced growth and condition indices likely are a consequence of improper nutrition among fluoxetine-treated mussels. Any level of fluoxetine significantly affected the gonadosomatic index after 47 days. The results from this study on mussels fill an important data gap, highlighting organism-level effects of chronic exposure periods; such data more explicitly identify the impacts of pharmaceuticals and other contaminants on marine communities and ecosystems. Fluoxetine has also been documented to affect the behavior of fish and invertebrates, including freshwater and marine bivalves, crustaceans, and fish. Given that other crustaceans exhibited increased activity levels under fluoxetine exposure, we hypothesized that this would subject them to greater predation risk. In our second exposure study, we assessed whether a similar range of fluoxetine concentrations used in the mussel study altered the risk behavior of the Oregon mud crab, Hemigrapsus oregonensis, in response to a common predator, the red rock crab, Cancer productus. We conducted this study for 60 days, conducting day and night behavioral trials (with and without predators) four times a week. We found that crabs exposed to any amount of fluoxetine (3 or 30 ng/L) had increased activity levels relative to controls; however behaviors of 3 ng/L-spiked crabs were not always significantly different from controls. Among control crabs, day and night trials yielded similar results, where a clear response to the addition of the predator was observed. Crabs dosed with fluoxetine exhibited more foraging and active behaviors in the presence of the predator. Additionally, crabs spiked with fluoxetine at 30 ng/L had the greatest risk of mortality either by predation by red rock crabs or due to more aggressive behaviors among conspecifics. The results of this study shed light on a particularly unexplored area of contaminants research: how do psychoactive pharmaceuticals affect animal behavior when exposed to the low concentrations persisting in the aquatic environment for a prolonged period of time?