Distinct temperature stressors acting on multiple ontogenetic stages influence the biogeography of Atlantic blue crabs

To understand and predict shifts in species distribution in a changing climate, it is important to consider the exposure and sensitivity of multiple life history stages, particularly for marine species with complex life cycles. In this study, we examined spatio-temporal trends in the abundance of the blue crab Callinectes sapidus and how different temperature stressors acting on multiple ontogenetic stages may affect the species' current and future distribution across the Atlantic coast of the USA. Since 1975, crab abundance has remained constant or increased in the northeast and northern mid-Atlantic regions but declined in the southern mid-Atlantic and southeast. In the northeast, abundance changes and the location of the northern range boundary appear to be dictated primarily by lower thermal constraints on summer larval stages and may be reinforced by chronic winter cold stress on juveniles and adults. In the mid-Atlantic, acute winter cold stress on juveniles and adults may regulate crab abundance, whereas in the southeast, temperature stress is likely not limiting or directly driving abundance declines. Temperature projections suggest a potential for northward range expansion and increased abundance in the northeast. In the northern mid-Atlantic, however, changes in the duration, magnitude, and phenology of summer temperatures may have complex effects on crab reproduction. Our results highlight how past and future changes in environmental suitability can vary non-uniformly both within and beyond a species' current range, and the value of examining multiple life history stages and aspects of temperature stress.