The distributions of marine ectotherms are governed by physiological sensitivities to long-term trends in seawater temperature and dissolved oxygen. Short-term variability in these parameters has the potential to facilitate rapid range expansions, and the resulting ecological and socioeconomic consequences may portend those of future marine communities. Here, we combine physiological experiments with ecological and demographic surveys to assess the causes and consequences of sudden but temporary poleward range expansions of a marine ectotherm with considerable life history plasticity (California market squid, Doryteuthis opalescens). We show that sequential factors related to resource accessibility in the core range may drive these expansions—the buildup of large populations due to competitive release, and climate-associated temperature increase and oxygen loss that constrain aerobic activity. We also reveal that poleward range expansion alters the body size—and therefore trophic role—of invading populations, with potential negative implications for socioeconomically valuable resident species. To help forecast rapid range expansions of marine ectotherms, we advocate that research efforts focus on factors impacting resource accessibility in core ranges. Determining how environmental conditions in receiving ecosystems affect body size, and how body size is related to trophic role, will help refine estimates of the impacts of future marine communities.

This excel file includes: envt_data_goa—seawater temperature trends in GOA determined from measurements reported by referenced data sources; abundance_data_goa—processed catch data of squid (presence/absence) in GOA from referenced data sources; pcrit_rmr_temp—critical oxygen partial pressures and routine metabolic rates for California market squid; pcrit_rmr_squid_metadata—metadata for squid specimens used in pcrit_rmr_temp; aerobic_scope—metabolic rates used for aerobic scope determination in California market squid, including those from referenced data sources; envt_data_ccs—seawater temperature and dissolved oxygen trends in CCS determined from measurements reported by referenced data sources; abundance_data_ccs—processed catch data of squid, anchovy, and sardine (counts) in CCS from referenced data sources; age_size_maturity_goa_ccs—age and size at maturity of California market squid in the GOA and CCS in 2016 and 2017; size_maturity_ccs_time—size at maturity of California market squid over the study period in the CCS; isotopes—carbon and nitrogen stable isotope data for GOA species, including those from referenced data sources; energy_density_proximal_comp—energy density, lipid content, and protein content data for GOA species, including those from referenced data sources.