Predator chemical cues increase growth and alter development in nauplii of a marine copepod

Copepods are a fundamental trophic link in the marine food web. While much attention has been devoted to the role of temperature and food for copepod development and growth, little is known about how marine copepods adjust their life history according to the prevailing predation risk. This is striking, considering the potential advantage of risk-sensitive life history, and the many reports of freshwater zooplankton showing strong effects of risk cues on growth and development. Here, we measured growth and development in nauplii of the marine copepod Temora longicornis. We incubated newly hatched nauplii individually with or without a predator chemical cue. Individuals were followed and measured repeatedly over time, generating highresolution data. We estimated treatment-specific stage transition probabilities from daily molting frequencies. The nauplii showed an increased growth rate when exposed to fish kairomones. However, the corresponding response in development differed between stages, with the later naupliar stages generally displaying a higher molting probability and higher body mass (ash-free dry weight) per stage. These results suggest that development and growth in marine copepods is flexible and sensitive to predation risk. Our findings also indicate that investment in growth might be beneficial in copepods despite higher visibility.