PREDICTING THE IMPACTS OF OCEAN ACIDIFICATION ON THE SPATIAL AND PHYLOGENETIC STRUCTURE OF THE GLOBAL MARINE BIVALVE FAUNA

Ocean acidification (OA) is a pressing anthropogenic threat to marine biological resources and diversity. Among Bivalvia, high temperatures and low pH disrupt metabolic processes, interfering with shell formation and maintenance and causing dissolution-driven stress or mortality. We present a trait-based approach to assess where, geographically and phylogenetically, the global bivalve fauna may be most susceptible to OA. Many bivalve-specific traits are known to interact with OA, but four are most frequently discussed and experimentally measured: shell mineralogy, size, thickness, and organic content. We evaluated the spatial and phylogenetic distribution of these traits across the class (5960 shelf-depth species) to anticipate how OA may globally affect bivalves, which are an important component of ecosystems and human diets and a >$20 billion/yr industry. Each trait was scaled from 0-1 and then summed to create a species-specific composite OA resistance score, with higher values indicating higher OA resistance. These scores approximate a species’ robustness to shell dissolution, not its possible physiological response (e.g. in metabolic rate, lipid content, exterior pH balance). We find that, globally, the median composite resistance score is 1.25 (ranging 0.2-3). Both composite and single-trait scores indicate relatively strong threat to the entire biota, assuming uniform global change in OA, with Antarctic taxa as the most vulnerable (Antarctic median=0.9). If mineralogy alone is the crucial driver of OA resistance, then the zone of lower resistance includes southern Oceania, South America, South Africa, and the high northern latitudes (median=1.1). Phylogenetically, exploited species in Pteriomorphia (oysters, scallops) show higher resistance to OA than exploited species in Imparidentia (cockles, quahogs, surf and pismo clams). This trait-based approach provides hypotheses for the impacts of OA on international fisheries and natural communities and informs climate-conservation policy in the face of rapid anthropogenic climate change, which requires rapid risk assessments. This approach also enables similar targeted evaluations of extinction selectivity among other groups, climate factors, and OA events in the geologic past (e.g. end-Permian, Paleocene-Eocene).