Sand shrimp, Crangon septemspinosa Say, are important to the trophic dynamics of coastal systems in the northwestern Atlantic. To evaluate predatory impacts of sand shrimp, daily energy requirements (J ind.−1 day−1) were calculated for this species from laboratory estimates of energy losses due to routine (RR), active (RA), and feeding (RSDA) oxygen consumption rates (J ind.−1 h−1), coupled with measurements of diel motile activity. Shrimp used in this study were collected biweekly from the Niantic River, Connecticut (41°33′N; 72°19′W) during late spring and summer of 2000 and 2001. The rates of shrimp energy loss due to RR and RA increased exponentially with increasing temperature, with the magnitude of increase greater between 6°C and 10°C (Q10=3.01) than between 10°C and 14°C (Q10=2.85). Rates of RR doubled with a twofold increase in shrimp mass, and RSDA was 0.130 J h−1+RR, irrespective of shrimp body size. Shrimp motile activity was significantly greater during dark periods relative to light periods, indicating nocturnal behavior. Nocturnal activity also increased significantly at higher temperatures, and at 20°C shifted from a unimodal to a bimodal pattern. Laboratory estimates of daily metabolic expenditures (1.7–307.4 J ind.−1 day−1 for 0.05 and 1.5 g wet weight shrimp, respectively, between 0°C and 20°C) were combined with results from previous investigations to construct a bioenergetic model and make inferences regarding the trophic positioning of C. septemspinosa. Bioenergetic model estimates indicated that juvenile and adult shrimp could meet daily energy demands via opportunistic omnivory, selectively preying upon items of high energy content (e.g. invertebrate and fish tissue) and compensating for limited prey availability by ingesting readily accessible lower energy food (e.g. detritus and plant material).