Marine environments are becoming more acidic as a result of increased atmospheric levels of carbon dioxide; this gas dissolves in sea water and is driving a process known as ocean acidification. However, organisms that live on the ocean floor (e.g. crabs, sea stars and oysters) experience, as a result of their biological activity, daily variations in their pH (acidity) that are greater than those caused by the increased levels of carbon dioxide in the atmosphere. This project addresses the comparative effects on porcelain crabs of increased ocean acidity (which changes slowly over years) with the daily variation in pH that these animals experience. The impacts of simultaneous changes in pH and temperature will be assessed, and it will be determined if early life history stages (i.e., crab larvae) are more sensitive to ocean acidification than adults. The responses that will be measured include calcification of the shell, metabolism, altered expression of genes and the modification of proteins. This research is expected to produce new and ecologically important information, across multiple levels of biological organization, about the impacts of ocean acidification on a coastal marine organism.
Broader Impacts: This research will provide interdisciplinary training for graduate and undergraduate students in biochemistry, genomics, physiology and ecology. Students who are members of groups underrepresented in science will be recruited through programs at the San Francisco State University Student Enrichment Opportunity office, and through collaboration between Cal Poly and Hancock University. The investigators will incorporate this research in their undergraduate physiology classes, which emphasize active learning. A workshop on proteomics for researchers interested in ecological physiology will be conducted at Cal Poly San Luis Obispo. The investigators will present public lectures on ocean acidification and climate change, and write articles on these topics in the popular press. Teacher training workshops designed to enhance secondary education in climate change biology will be conducted at the Romberg Tiburon Center and Cal Poly San Luis Obispo.
Intellectual Merit: Increased atmospheric carbon dioxide (CO2) has consequences including climate change, ocean warming and ocean acidification. We examined responses of intertidal zone porcelain crabs to ocean warming and acidification. These crabs experience variable temperature and pH. At high tide variation in pH is caused from day-night cycles of photosynthesis (which elevates pH) and respiration (which decreases pH) and by upwelling. At low tide temperatures can rise by more that 20°C during hot sunny days. Temperature and pH variability are expected to increase under climate change, so crab adult and embryo responses to pH and temperature variability are important to understand. Crab larvae live in the open water where the pH and temperature variation is less than on the seashore. Comparison of adult, embryo, larvae and juveniles is important to fully characterize how crabs will fare in future ocean conditions. Studies have been (are being) performed as the thesis projects of eight graduate students. Projects also involved two additional graduate students, four undergraduate students and one postdoctoral fellow. A brief summary of our findings and products follows: We found that the metabolic rates of crab embryo, larvae and juveniles were overall lowered by reduced pH, though the responses depended on which family the crabs were from. This finding indicates that there is diversity across individuals in response to ocean acidification that could represent specific genotypes that are pre-adapted to future conditions, or that represent trans-generational effects of response to environmental change, the mechanisms of which are yet to be determined. These findings were published in two articles in the Journal of Experimental Biology that were highlighted in the journal’s news & view’s section "inside JEB." The lead authors were MS students Lina Ceballos-Osuna and Hayley Carter. We found that temperature and pH variation interact in adult crabs to lower overall metabolism but increase the fraction of metabolism spent on basic physiological maintenance. This finding suggests that in the future crabs could have less energy for growth and reproduction when they are exposed to increased thermal variation during low tide and increased pH variation during high tide. This finding is going to be published in mid-November 2014 in the Journal of Experimental Biology, and will be highlighted as the editor’s choice and in the journal’s news & view’s section "inside JEB," plus has been chosen as the cover of that issue. Lead author is MS Student Adam Paganini. We are currently testing the follow-up hypothesis to the above finding by examining growth and metabolism of juvenile crabs under thermal and pH variation. One run of the experiment has been completed and showed reduced growth, supporting our energetic hypothesis. Lead is MS student Carley Turner. We found that exposure to reduced pH changes the mineral composition of the exoskeleton of the claw and carapace of four species of porcelain crabs. Those changes were not uniform across species, and were related to intertidal location and geography. The manuscript will soon be submitted to the Journal of Experimental Biology. Lead author is MS student Tessa Page We found that exposure to reduced pH and thermal stress interactively impacts the development and metabolism of embryos of porcelain crabs from the southwestern coast of England. Thermal stress had a stronger effect than low pH, though the effect was not seen equally across broods of embryos. This finding is currently being prepared for publication. Lead is PhD student Eric Armstrong. We are testing the exposure to pH and thermal stress in embryos of a California porcelain crab, with the addition of genetic analyses of mother and father to determine whether multiple paternity plays a role in the variability of metabolic and developmental responses to environmental stress. Lead is MS student Thomas Yockachonis. We are examining gene expression profiles using genomics approaches in two species of adult porcelain crabs that have been exposed to varying pH and temperature with the goal of identifying differentially expressed genes related to acidification and warming. Next generation sequencing has been completed and we are presently finishing bioinformatics analyses. Lead is PhD student Eric Armstrong. We have used cDNA microarrays to examine changes in gene expression associated with rearing larval and juvenile crabs under low pH conditions. There were zero differentially expressed genes using microarrays, and so this work did not lead to a publication. Lead was PhD student Dave Hurt. Additional products include four review papers on adaptation to ocean acidification, and genomic approaches in environmental biology. Broader Impacts: In addition to student training, this project established of an international collaboration with Piero Calosi with whom I am writing a children’s book on ocean acidification. Presentations on ocean acidification were made in a variety of public forums and outreach programs.
