Award: OCE-1636191

PROJECT OUTCOMES As humans release carbon dioxide into the atmosphere, approximately a third enters the ocean, altering the chemistry of seawater. This process, termed ?ocean acidification? because it lowers the water?s pH, reduces the ability of many marine organisms to form shells and skeletons, and can also disrupt their behavior. The latter phenomenon is incompletely understood, and continues to be the focus on ongoing research. Behavioral impairment due to ocean acidification is especially relevant because every species interacts with other species, and behavior often underlies the character of such interactions. In this National Science Foundation project, we examined behavioral impairment by ocean acidification in a model food web, to begin to isolate how human-induced chemical changes to seawater influence both individual organisms, as well as relationships among those organisms. Understanding such relationships is crucial because they often dictate not only the ability of individual species to succeed, but also the broader community implications of their successes or failures. In our work, we focused on a simple but classic food web found on temperate rocky shores along the west coast of the U.S. This food web consists of sea star predators, their snail prey, and seaweed consumed by the latter. It echoes the kinds of feeding links that exist quite widely in shoreline marine systems. Our research demonstrated that the snails we examined (black turban snails, Tegula funebralis, one of the most common grazers regionally) are vulnerable to chemical changes to seawater associated with lower pH. In particular, under ocean acidification conditions, the snails fail to respond appropriately to waterborne cues emitted by sea stars (ochre and six-armed stars, Pisaster ochraceus and Leptasterias hexactis), and no longer seek refuge to avoid predation. As one might expect, this effect then results in snails experiencing elevated mortality because sea stars are able to consume the snails more easily. Less obviously, we also found that even though fewer snails remain to feed on their seaweed food sources (Ulva sp. and Macrocystis pyrifera), the abundance of seaweed actually declines. This latter result derives from the fact that ocean acidification makes the snails ?foolhardy,? such that snails that are not consumed by sea stars feed as if sea stars are absent ? that is, the snails feed in place of attempting to hide from their predators. The net consequence is that even though fewer snails remain under ocean acidification, those that do remain graze on seaweeds at higher rates, which more than compensates for their lower numbers. We demonstrated that these findings hold in carefully controlled laboratory experiments, as well as in field experiments where we manipulated the chemistry of seawater in dozens of replicate tidepools along the shore. Additional experiments also explored the degree to which multiple species of snails might respond differently to ocean acidification in the presence of predators. These latter research efforts revealed that snail species that live at deeper depths, and thus do not experience the more extreme excursions in pH characteristic of tidepools, exhibit reduced tolerance to strong deviations in ocean chemistry. Together these scientific insights help guide expectations for how coastal marine species and communities will respond to ocean acidification in coming decades. The project also had important broader impacts via training of next-generation scientists, and in informing the public and policymakers about ocean acidification. The primary Ph.D. student funded by the grant has now advanced into a permanent tenure-track faculty position at a top university, and a second Ph.D. student who also received funding from the project completed their degree and was awarded a prestigious National Science Foundation Postdoctoral Fellowship. This second graduate student was a member of an underrepresented group. Multiple undergraduates, including four Latinx individuals, received STEM training and direct exposure to the research enterprise, and a Canadian Ph.D. student who visited our lab for six months developed components of her thesis in collaboration with our team. Information about ocean acidification was transmitted to the public (10,000 individuals per year) through a long-term institutional program linked to our research efforts, and the PI provided scientific input to various legislative members and their staff regarding ocean acidification and other research topics of societal importance. Last Modified: 10/26/2021 Submitted by: Brian P Gaylord