## 4 Materials and Methods  
### Microcalgae and Rotifer Cultures  
Axenic _Microchloropsis gaditana_ CCMP 526 was obtained from National Center for Marine Algae and Microbiota (NCMA at Bigelow Laboratory, East Boothbay, ME, USA). Axenicity of the culture was defined by NCMA standards and _M. gaditana_ cultures were not further tested in house. _M. gaditana_ cultures were grown in modified ESAW medium [40] made with 7.5 mM NaNO\({}_{3}\) and 0.5 mM Na\({}_{3}\)PO\({}_{4}\) and MilliQ water. Stock cultures of _M. gaditana_ were grown at 20 \({}^{\circ}\)C, a light intensity of 100 \(\upmu\)mol m\({}^{-2}\)s\({}^{-1}\) and a 16:8 h light:dark cycle. Volatilomics experiments were conducted under the same conditions as in [PERSON] et al. 2019 [24], except 80:20 N\({}_{2}\)/O\({}_{2}\) was used as the VOC-free research grade air with a purity of 99.999% (Matheson Tri-Gas, West Sacramento, CA, USA). Briefly, cultures were continuously sparged with 1% CO\({}_{2}\) and 99% air for a total mass flow of 900 cc min\({}^{-1}\) split equally across the six culture vessels (150 cc min\({}^{-1}\) sparging rate for each individual sample). Xenic rotifer cultures of _Brachionus plicatilis_ (Reed Mariculture, Campbell, CA, USA) were concentrated, counted, and added to experiments in the same way as described in [24]. Cultivation of _M. gaditana_ and _B. plicatilis_ at 15-L scale was carried out according to the methods described in [24] with few differences, detailed herein. All three experiments of _M. gaditana_ and _B. plicatilis_ (referred to as \"A + R Experiments 1-3\", or \"A + R 1-3\") utilized six 20-L carboys. Prior to algal inoculation, 15 L of ESAW media were 0.2 \(\upmu\)m-filtered, added to each of the six carboys, and then media blank headspace samples were collected for 1 h on SPME fibers (described further below). All six carboys were then inoculated with _M. gaditana_ to a final concentration of 5-6 \(\times\) 10\({}^{6}\) cells mL\({}^{-1}\) for A + R Experiments 1 and 3, and 12 \(\times\) 10\({}^{6}\)_M. gaditana_ cells mL\({}^{-1}\) for A + R Experiment 2. For all experiments, microalgae were grown under the same conditions as described in [PERSON] et al. (2014). (Briefly: 2000 \(\mu\)mol m\({}^{-2}\)s\({}^{-1}\) of 24 h light, 22-25 \({}^{\circ}\)C, 150 cc min\({}^{-1}\) sparging of 1% CO\({}_{2}\) through bubbler). For all A + R Experiments, 6.6 \(\times\) 10\({}^{5}\) live rotifers (final concentration of 44 rotifers mL\({}^{-1}\)) were added to three of the six _M. gaditana_ cultures (carboys 4, 5, and 6, abbreviated C4, C5, C6). For A + R Experiments 1 and 2, the rotifers were added to the algae cultures 24 h after algae inoculation and for A + R Experiment 3, the rotifers were added to the algae 48 h after algae inoculation. Rotifers were concentrated, counted, and prepared for addition to cultures as described previously (2014). Fewer rotifers were used for these experiments, in comparison to [PERSON] et al. (2014), due to the slightly smaller size of the _M. gaditana_ cells and presumed higher grazing rate by _B. pliattilis_. Freeze-Thawed Algae (FTA) experienced cellular disruption in the absence of rotifers by repeatedly freeze-thawing concentrated _M. gaditana_ before adding to media (these experiments are referred to as \"FTA Experiments 1-3\", or \"FTA 1-3\"). These experiments had a similar setup (e.g., ESAW media, CO\({}_{2}\)/air sparging rates, initial algal concentration) as the previously described algae + rotifer experiments except that the final culture volume for each of the six replicates was 900 mL, held in glass 1-L Pyrex containers. After media blank headspace samples were collected by SPME (as described previously for algae + rotifer experiments), _M. gaditana_ inoculum was concentrated by gentle centrifugation (2500\(\times\)_g_) down to ~100-120 mL and then evenly divided between six conical tubes for each of the six Pyrex containers in the experimental setup. Three of these conical tubes (each containing ~15-20 mL of concentrated _M.