## 4 Materials and Methods
### SPME Headspace Sampling and GC-MS Data Acquisition  
VOCs from the headspace of each culture and media control were collected using portable field sampler solid-phase microextraction (SPME) fibers at the same time as algal density measurements. The methodology of VOC sampling was the same for the algal damage occurring via rotifer grazing (A + R Experiments 1-3) and or freeze-thaw cellular disruption (FTA Experiments 1-3). The collection procedures were similar to those described in [PERSON] et al. (2014), briefly summarized here with relevant modifications. Bi-phasic coated SPME fibers with 65 \(\mu\)m polydimethylsiloxane/divinylbenzene (PDMS/DVB) coat ings (Supelco, Bellefonte, PA, USA) were introduced to the headspace above culture vessels for 60 min during relevant experimental timepoints. Three vessels were prepared as biological replicates. For the A + R Experiments, two SPME fibers were introduced to each vessel and the reported VOC signal of each biological replicate (_n_ = 3) per timepoint per condition is the average of \(n\) = 2 technical replicates (two SPME fibers per vessel). For A + R experiments 1 and 2, SPME timepoints were collected at 48, 72, and 96 h post algae inoculation, and at 72, 96, and 120 h for A + R experiment 3 (as indicated by * in Figure 1). For the freeze-thaw cellular disruptions, one SPME fiber was introduced to sample each vessel, resulting in \(n\) = 3 biological replicates with a single technical replicate (one SPME fiber) per timepoint per condition. For FTA Experiment 1, only 24 and 48 h SPME sampling timepoints were collected, but for FTA Experiments 2 and 3, SPME sampling was performed at 1, 6, 24, and 48 h timepoints. Additionally, an unexposed fiber representing a \"travel blank\" to detect extraneous volatiles deposited during the storage process was included with the culture samples. All SPME fibers were subsequently stored at 2-4 \({}^{\circ}\)C and analyzed by GC-MS within 2-3 weeks of VOC sample collection. VOC data acquisition utilized an untargeted GC-MS approach performed using an Agilent 5975 T GC-MSD (Agilent Technologies, Santa Clara, CA, USA), employing the same instrument and temperature program used in [PERSON] et al. (2018). Instrument performance was monitored using a commercial reference mixture (S-22329-R1; AccuStandard, New Haven, CT, USA) to evaluate variation in day-to-day performance and to calculate retention indices.  
Analytical reference standards for trans-\(\beta\)-ionone (\(\geq\)97.0% purity, catalogue #16976) and \(\beta\)-cyclocitral (\(\geq\)97.0% purity, catalogue #16976) were purchased (Sigma-Aldrich, St. Louis, MO, USA) to verify if putative identifications of select biomarkers were accurate. The standards were injected neat (1 \(\mu\)L) into the GC inlet. The analytical standards were analyzed alongside an injection of the commercial reference mixture (AccuStandard) for determination of retention indices values. Resultant mass spectral fragmentations from the analytical standards were then compared to those of experimentally observed biomarkers. The same GCMS method detailed in (2018) was also used for these analytical standards except that the analytical standards method required a 4 min solvent delay.