Award: EF-1416690

Since the industrial revolution, the earth's oceans have become more acidic due to absorption of carbon dioxide (CO2) from the combustion of fossil fuels. In the early 21st century, biological impacts of this "ocean acidification" ("OA") were first noted in terms of damage to marine organisms, such as snails, whose shells are made of calcium carbonate minerals. These shells fail to grow, or even begin to dissolve, as seawater becomes more acidic. Most studies of OA have focused on discerning the effects of the average levels of OA that will occur in open-ocean ecosystems, as predicted by expectations for rising atmospheric CO2 in the decades ahead. However, the situation is much more complicated in near-shore coastal ecosystems, where high levels of biological productivity generate both large increases in dissolved CO2 (from the respiration of organisms) and decreases in dissolved CO2 (from the photosynthesis of algae and marine plants), relative to a steadily-rising baseline of CO2 from the atmosphere. These biological processes are also affected by human impacts such as nutrient pollution and environmental temperature increases. Measures of OA, such as seawater pH, thus fluctuate much more in coastal environments than in the open ocean. The importance of coastal environments is underscored by the fact that about 40% of the world's human population lives within 100 km of a coast, and that these environments support a disproportionate share of global fisheries and other marine ecosystem services. Our project examined the effects of high levels of OA on the slippershell snail, Crepidula fornicata, an important member of coastal ecological communities both in its native range in the northeastern USA, and in parts of the Pacific Northwest and Europe where it has become established as an invasive "pest" species. We studied effects of OA on the development of the larval and juvenile stages of this animal, because larval forms of other marine organisms are known to be especially sensitive to OA and because dispersal and growth of larvae and juveniles are so important to the distribution of adult populations. Moreover, a great deal is already known about the growth and development of the larvae of C. fornicata, what factors control the metamorphosis or transition from larval to juvenile forms, and how environmental stressors experienced during the larval period have persistent effects on the growth of juveniles after metamorphosis. We found that OA depressed larval growth only at a rather severe level of acidification (pH 7.5) that will not be reached in the open ocean in the foreseeable future, but that sometimes occurs in coastal habitats today. Less-severe OA conditions had no detectable effect on larval growth, but larval experience of moderate OA inhibited the growth of juveniles after metamorphosis, even after the OA stress had been removed. Furthermore, this juvenile growth inhibition by larval OA stress was more pronounced in individuals that had been reared with low levels of nutrition as larvae. Poorly-fed larvae normally take longer than well-fed larvae to become "competent," or developmentally ready to metamorphose into juveniles. Under moderate OA conditions, this developmental difference between poorly-fed and well-fed larvae became more pronounced. OA treatments had no effect on the ability of competent larvae to perceive sensory cues that trigger metamorphosis. The growth of juveniles after metamorphosis, like that of larvae before metamorphosis, was also remarkably resilient to OA, only declining at a seawater pH of about 7.5. However, more moderate OA conditions lowered the breaking strength of juvenile shells, even though these shells grew just as fast in length and weight as the shells of juveniles growing under less-acidified control conditions. This result points to the likelihood that OA may affect survival of marine organisms in subtle ways. We found that OA treatments changed the expression patterns of a large number of genes that are related to growth and metabolism; analysis and interpretation of these genomic data are continuing. We hope that ongoing research will reveal the biological mechanisms by which C. fornicata and other resilient organisms respond physiologically and evolutionarily to acidified environments, and how these mechanisms differ from those in less-resilient species. Such a comparative organism-level perspective should give insight into how coastal marine communities may change in the face of challenges from OA in concert with other environmental stressors. Last Modified: 11/09/2018 Submitted by: Anthony Pires