Signals in flux: Investigating the seasonal turnover of the diel vertical migration-inducing kairomone 5α-cyprinol sulfate

5α-cyprinol sulfate (CPS) is a chemical signal released by cyprinid fish that plays a crucial role in predator-prey interactions by inducing diel vertical migration (DVM) in Daphnia , a key process driving freshwater ecosystem dynamics. While CPS-mediated DVM has long been considered a stable and predictable response to predator abundance, this study challenges previous assumptions by demonstrating that CPS undergoes rapid turnover in aquatic systems. We show that CPS exudation is tightly linked to fish feeding intensity, independent of fish size, while microbial degradation emerges as the dominant removal process, with degradation rates reaching up to 85.7% per day in lake water. Seasonal field data from a mesotrophic lake reveal that CPS concentrations range from 40 to 900 ng/L over a season, peaking in late summer, putatively indicating increased fish feeding and shifts in prey availability. Using an integrated approach combining laboratory feeding trials, field sampling, and predictive modeling, we present a temperature-dependent framework that captures the interplay between CPS exudation and degradation. Our findings highlight a fundamental reconsideration of CPS as an environmental cue: rather than reflecting predator abundance, CPS concentrations primarily track predator feeding activity, dynamically modulating the strength of DVM and its cascading effects on freshwater food webs. This study provides the first in-situ quantification of CPS turnover, offering new insights into the temporal variability of chemical signaling and its ecosystem-wide consequences in fluctuating aquatic environments.