Graduate Thesis Or Dissertation


So Long and Thanks for All the Sponge: Cryptic Intertidal Communities, Consequences of Ocean Acidification, and New Directions for Science Education Public Deposited

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  • The current generation of scientists will be asked to mitigate climate change, stall biodiversity loss, and protect ecological communities. These are tasks that require a knowledge of both ecological and social systems to be undertaken successfully. Therefore, my dissertation spans the fields of community ecology and social sciences in an attempt to prepare to solve problems that are multidisciplinary by nature. My ecological research (Chapters 2-4) utilizes rocky intertidal ecosystems as a platform to study how oceanographic processes impact ecological communities. Intertidal communities, and the processes that maintain them, are strongly connected to large-scale oceanographic processes; previous research has highlighted the connection between large-scale processes and general patterns among sites. In Chapter 2, I examine how site level characteristics of community structure and recovery from disturbance predict patterns in previously uncharacterized cryptic surge channel communities. Using multivariate methods, I provided a novel quantitative description of cryptic surge channel communities and their patterns of recovery after disturbance. I quantified the relative importance of site and environmental factors on patterns of community composition, diversity, and recovery in these two communities. I found that site-level patterns in species dominance (e.g., macrophyte versus sessile invertebrate) predict patterns of community composition in cryptic communities. Furthermore, patterns of recovery and recovery rates were consistent with site-level patterns, suggesting that site-level processes are important across all habitat types within a site. This finding validates the previous assumption that large-scale oceanographic processes (e.g., upwelling, productivity, and recruitment) are closely linked to nearshore ecosystems and that this pattern is evident across distinct habitat types. Ocean acidification (OA), defined as the reduction in the pH of global oceans, is predicted to have negative impacts on marine invertebrates. Within the past two decades there have been hundreds of studies on the effects of OA on the fitness, survival, and growth of many marine organisms, and yet there are several large gaps in our understanding. Many OA studies focus on one population (e.g. only sample from one site/location) of a widespread species and then make generalizations about that species as a whole. This is problematic for species that are spread between habitats with different levels of acidification. My work in Chapters 3 and 4 addresses the response of multiple populations of an important intertidal invertebrate to ocean acidification conditions on the Oregon coast; I describe the impacts of OA on the early life history (Chapter 3) and adult physiology (Chapter 4) of the common breadcrumb sponge Halichondria panicea. To investigate if H. panicea are adapted to local conditions, I utilized the persistent pattern of acidification that exists on the cape scale along the Oregon coast. I compared the responses of sponge populations that persist in areas of high, intermediate, and low acidification. I used both field and laboratory experiments to investigate the potential for local adaptation or acclimatization to OA conditions in H. panicea. In Chapter 3 I found that sponge larvae from areas that experience persistently high levels of ocean acidification may be less resilient to future levels of OA vs. larvae from other less acidified regions. Negative carryover effects for early exposure during brooding may result in increased larval mortality and faster rates of settlement; there were no effects of treatment on post-settlement processes for either population. Chapter 3 highlights a novel response of sponges to OA and reveals a potential population bottleneck during the critical larval stage for pre-exposed sponges under future OA conditions. Chapter 4 builds on the work of Chapter 3 by examining the response of adult sponges from high, middle, and low areas of OA along the Oregon coast. I used a common garden approach to untangle the effects of environmental acclimation and adaptation in a reciprocal transplant and mesocosm experiment. I observed changes in survival, mass, and Chlorophyll a (Chl- a) concentration. Consistent with Chapter 3, I found that prior exposure to OA resulted in increased mortality during the transplant and mesocosm experiment, although we found no evidence of treatment- or population-dependent effects on mass and chlorophyll a concentration in H. panicea populations. Combined, results of Chapters 3 and 4 suggests that sponges from highly acidified regions may be living near a threshold, past which the fitness of both larvae and adults would be compromised, with implications for the population as a whole. Understanding how climate change will impact ecological communities is a large and difficult task and we therefore need to attract and retain science students to meet this demand. Recent work has shown that undergraduate research experiences may increase science technology engineering and math (STEM) identity and ultimately persistence down the STEM pipeline, however, the link between these research experiences and the formation of participant STEM identity remains understudied. Chapter 5 addressed this research need by clarifying the role of undergraduate research experiences (UREs) in developing STEM identity and contributing to persistence of individuals within STEM. In chapter 5, I applied several analytical models of STEM identity to quantify pre- versus post- shifts in the STEM identity of National Science Foundation Research Experiences for Undergraduates (REUs) using quantitative and qualitative pre/post survey data. Quantitative survey results indicated that STEM identity did not change with REU program participation. However, qualitative responses indicated that participation facilitated science learning, personal growth, and general identity development. I examined qualitative answers to understand the discrepancies between survey results and long answer questions. I found that qualitative answers related to science learning outcomes were associated with the acquisition of specific science skills and research techniques and did not translate to broader scientific understanding. These findings are problematic because to develop a STEM identity and persist in STEM, learners need a broad understanding of the scientific process to be incorporated into the culture of science, which is vital part of forming a strong STEM identity and is therefore linked to STEM persistence. Overall my dissertation builds on our understanding of how ecological and social communities persist in the face of change and challenge. I provide a novel description of a new habitat type, describe the response of a dominate taxa to ocean acidification, and provide insight into how we can improve science education to meet the growing demand for STEM professionals.
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