Rapid range expansion of a marine ectotherm reveals the demographic and ecological consequences of short-term variability in seawater temperature and dissolved oxygen

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.