A dominant theme in explaining intraspecific latitudinal gradients in size is the temperature-size rule which states that intraspecific growth rates decline but maximum sizes increase with declining temperatures over a species’ geographic range. The temperature-size rule has accumulated considerable support in poikilotherms, yet amongst marine taxa, few reports issue from studies on the Bivalvia despite the underlying physiological conducement provided by the differential allometric scaling of respiration rate and filtration rate. Amongst the Bivalvia, the mactrid Spisula solidissima (Atlantic surfclam) is noteworthy for its size, the extensiveness of its latitudinal range, and its biomass dominance on the continental shelf. Here, the demographics of S. solidissima are evaluated with respect to the temperature-size rule, followed by contemplations on the impact of climate change on the species and its management. Analysis of size-frequency distributions from the southern range boundary near the Chesapeake Bay to Georges Bank, identify the anticipated trend of increasing maximum size with decreasing temperature. Application of a metabolic energetics model shows that the dramatic variations in size accrue from the direct physiological impact of geographic variations in temperature strongly modulated by variations in food supply. The influence of food likely explains the rarity of direct observations of the temperature-size rule in Bivalvia. Management measures based on the size frequency are discussed, and specifically regulatory size limits on landings are identified as incompatible with the temperature-size rule.