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.
Rickborn A. J., 2019. So long and thanks for all the sponge: cryptic intertidal communities, consequences of ocean acidification, and new directions for science education. PhD thesis, Oregon State University. 219 pp. Thesis.
