Zooplankton can serve as indicators of ecosystem health, water quality, food web structure, and environmental change, including those associated with climate change and ocean acidification (OA). Laboratory studies demonstrate that low pH and high pCO 2 associated with OA can significantly affect the physiology and survival of zooplankton, with differential responses among taxa. While laboratory studies can be indicative of zooplankton response to OA, in situ responses will ultimately determine the fate of populations and ecosystems. In this perspective , we compare expectations from experimental studies with observations made in Puget Sound (Washington, United States), a highly dynamic estuary with known vulnerabilities to low pH and high pCO 2 . We found little association between empirical measures of in situ pH and the abundance of sensitive taxa as revealed by meta-analysis, calling into question the coherence between experimental studies and field observations. The apparent mismatch between laboratory and field studies has important ramifications for the design of long-term monitoring programs and interpretation and use of the data produced. Important work remains to be done to connect traits that are sensitive to OA with those that are ecologically relevant and reliably observable in the field.