Anthropogenic stressors are omnipresent in marine environments and interfere with organisms of all sizes, from large whales to small organisms. We investigated potential interactive multistressor effects of increased temperature with chronic low-frequency sound on the development and movement patterns of the calanoid copepod Acartia tonsa, a model species for small marine zooplankton. Copepods were reared while exposed to chronic low-frequency sound around 15 and 22 dB re 1 μPa2 Hz−1 above control sound pressure levels at frequencies between 110 and 120 Hz, at 21°C (increased temperature) and 18°C (control temperature). For each sound and temperature scenario, we assessed after-incubation development rate, stage distribution, and movement patterns. We found that fewer copepods reached the developmental stages copepodites IV to VI in low-frequency sound conditions, even though warmer conditions increased developmental rate. By using high-speed videography in both control and low-frequency sound conditions, we observed that copepods showed more escape behaviors (drops) and fewer feeding-associated behaviors (helical swimming) when exposed to low-frequency sound (~ 42 dB higher than normal at 142 Hz). Copepods reared with added low-frequency sound showed fewer feeding-associated behaviors and did not reverse these trends despite the absence of added sound in their feeding environment. These significant behavioral changes suggest detrimental negative, life-long, consequences for copepods exposed to low-frequency sound.