The influence of loss of diversity on community dynamics and ecosystem functioning has recently received considerable attention. Although study of biodiversity has a long history within ecology, empirical investigations exploring consequences of loss have been rare. Because many factors confound diversity comparisons, experimental manipulations of diversity offer the most direct way of attributing cause to diversity loss. The effects of reduction in number of species will depend on the strength and sign of species interactions affected by loss of diversity. An experiment performed on a high zone, rocky intertidal community in which macroalgal diversity was manipulated demonstrated that effects of diversity loss will be highly dependent on which species are removed. However, effects of diversity reductions were strongest at the harsh end of a stress gradient where interactions were more positive. Thus, factors that affect the strength and sign of species interactions such as the degree of physical stress may serve as a rough guide to where the effects of diversity loss will be most severe. An assessment of the influence of diversity on community response to a strong physical perturbation was performed using an experimentally-induced thermal stress. Higher diversity treatments were most strongly affected directly by the stress because such treatments had higher abundance and therefore more biomass to lose. However, those same treatments recovered more quickly from the stress. Community recovery of initially low diversity treatments was slowed by persistence of non-typical states or slow recovery of dominant species. A simulation study was performed to assess the ability of different experimental designs to detect biodiversity effects. Our ability to predict consequences of changes in diversity will be dependent on our ability to distinguish the most influential biodiversity "components" within a system. This study uncovered a phenomenon that will be common in biodiversity studies: misidentification of one biodiversity component (e. g., an effect of a keystone species) as a different component (e. g., an effect of the number of species). I call this phenomenon "aliasing." Because of the complexity of biodiversity, experiments and observational studies will be highly susceptible to aliasing and, thus, results will require careful interpretation. / Graduation date: 1997

Understanding how large-scale processes (>100 kms) influence ecological communities is currently a major focus in ecology. In marine systems, coastal upwelling, a large-scale oceanographic process in which surface water pushed offshore by winds is replaced by cold, nutrient-rich water from depth, appears to cause variation in rocky intertidal communities. Along the central Oregon coast upwelling occurs intermittently during the summer while on the southern coast it begins earlier in the spring and is less variable throughout the summer. Coastal upwelling can affect rocky intertidal communities by altering the delivery of nutrients, larvae, and phytoplankton. I conducted three studies on both the southern and central Oregon coast to understand how differences in upwelling affect rocky intertidal community structure and dynamics. In the first study, I examined the recruitment and growth rates of sessile invertebrates (mussels and barnacles). Recruitment of both mussels and barnacles, and growth of mussels were consistently higher on the central Oregon coast than the southern coast. Upwelled water is nutrient-rich, so differences in upwelling are likely to affect growth rates of macroalgae. In the second study, I tested this hypothesis by monitoring the growth of two species of intertidal kelp at both central and southern coast sites. During El Ni��o years, when upwelling is sharply reduced on the central Oregon coast, algae may fare better at sites on the southern coast where upwelling is less affected. However, during years when upwelling is strong all along the coast, nutrient limitation does not appear to differentially affect macroalgal growth rates. Finally, in the third study, I examined the influence of upwelling on the interactions between microalgal primary producers and herbivorous limpets. I conclude that this interaction is complex and varies both within and between upwelling regions. My research suggests that a transition in upwelling from weak and sporadic on the central Oregon coast to stronger and more persistent on the southern Oregon coast drives the striking differences in rocky intertidal community structure and dynamics between these areas. / Graduation date: 2003

I examined the biomechanical factors that influence the sizes of intertidal macroalgae by studying a population of Fucus gardneri at Fogarty Creek Point, OR. I constructed a mathematical model to predict optimal sizes and probabilities of survival for Fucus under conditions of high and low wave exposure. Predicted optimal sizes of Fucus closely matched the mean observed sizes of plants collected from wave-exposed and protected locations. To test this hypothesis in the field, I reciprocally transplanted Fucus between wave-exposed and wave-protected sites and found that the degree of wave exposure did not affect survival, but did influence size. Large Fucus were tattered by waves at exposed sites, and small Fucus grew at protected sites. These results support the hypothesis that wave forces can set mechanical limits to size in Fucus. I experimentally examined the relative influences of wave-induced disturbance, competition and predation on the sea palm, Postelsia palmaeformis and its understory community at a wave-exposed site at Depoe Bay, OR. Postelsia recruitment was affected by seasonal variations in disturbance and was greatest in areas disturbed in winter. Postelsia were most abundant at mid-zone, wave-exposed sites, and their restriction to wave-exposed sites seems to be due both to; 1) the occurrence of predictable winter disturbances at these sites which remove mussels, thereby stimulating sea palm growth from the underlying rock, and 2) high water motion which enhances sea palm growth by increasing nutrient exchange and photosynthesis and preventing desiccation at low tide. Competition, disturbance and grazing were all important factors in structuring the Postelsia understory community. Postelsia were dominant competitors and their holdfasts overgrew low-lying plants which were torn loose with Postelsia when this kelp was dislodged by winter storm surf. In the absence of this predictable, seasonal disturbance, competitive understory species, such as Corallina dominated primary space. Intermediate levels of disturbance allowed for the highest understory species diversity. Limpets played a keystone role by grazing Postelsia, the competitive dominant during most of the year, and maintained high levels of species diversity in the algal understory. / Graduation date: 1995

ix, 119 leaves : ill., maps ; 28 cm Notes Typescript Thesis (Ph. D.)--University of Oregon, 1985 Includes vita and abstract Bibliography: leaves 108-119 Another copy on microfilm is located in Archives

Early life stages of many marine and diadromous fish species use sandy beach surf zones, which occur along >50% of the world's marine coastlines. This extensive habitat can provide juvenile fishes with an abundant supply of potential prey and the ability to hide from predators in its shallow turbid waters. Chinook salmon is an anadromous species that migrates to the ocean during their first (subyearlings) or second (yearlings) year of life. The majority of subyearlings reside in estuaries during their first summer season; however, a small number of juveniles also use surf zones. Early marine residence is considered a critical period for Chinook salmon due to high mortality rates; however the role of surf zones in Chinook salmon life history is unclear. Therefore, I determined the distribution of juvenile Chinook salmon on beaches of the eastern North Pacific, compared the migration and growth patterns observed in surf zones and estuaries, identified the factors that accounted for variation in juvenile surf zone catch, explored the factors that influence growth rate variation in surf zones and estuaries, and modeled how growth rates in these coastal habitats may vary in the near future with predicted changes in climate. The majority (94%) of juveniles were caught in surf zones adjacent to estuaries with trough areas, which are beach sections where sand moved by currents and waves produce a trench-like shape. Surf zone fish were collected in significantly lower numbers than estuarine juveniles but entered brackish/ocean waters at similar sizes. Juveniles in surf zones consumed similar organisms (gammarid amphipods, crustacean larvae and insects) as in estuaries. Furthermore, stomach fullness indices (average = 2% of body weight) and growth rates (average = 0.4 mm day�����) were similar in surf zones and estuaries. At one surf zone, juvenile catch was positively correlated to short-term specific growth rates (14 days prior to capture). A bioenergetics modeling approach indicated that given current conditions, consumption rates accounted for more of the variation in growth than prey energetic content and temperature. Climate models predict future increases in fresh water temperature (1.5 to 5.8��C), sea surface temperature (1.2��C) and wave height (0.75 m) that could influence estuarine and surf zone use. Therefore, I developed a local mixing model based on these predictions to estimate future surf zone and estuarine water temperatures in two of the watersheds studied. Based on these temperature projections and the bioenergetics model, I predicted how juvenile specific growth rates would vary in both habitats. I determined that increases in water temperature in both habitats would reduce specific growth rates by 9 to 40% in surf zones and estuaries if diet composition and consumption rates remain similar to present conditions. To compensate for the decline in growth, juveniles may increase their consumption rates or consume more energetically rich prey, if available. If they are not able to compensate, their size at the end of the season may be reduced, which could reduce their overall survival. These results confirm that a small number of suyearling Chinook salmon use sandy beach surf zones, mostly adjacent to estuary mouths, where they experience growth conditions comparable to estuaries. My findings indicate that, in certain situations, juvenile Chinook salmon surf zone use can be influenced by surf zone growth conditions, while variation in growth rates are themselves most strongly influenced by variation in consumption rates in surf zones and estuaries. Predicted changes in coastal western North American climate will likely modify juvenile growth conditions in the next 50 years, and potentially reduce overall survival. Additional insights into the potential impacts of climate change on juvenile salmon will require estimates of changes in the composition, energetic quality and abundance of prey communities inhabiting coastal environments. / Graduation date: 2013