## 1 Introduction
For these reasons, imaging flow cytometry [17; 18], and nucleic-acid hybridization techniques [19] are under study to automate, simplify, and expediate the pond contaminant monitoring process. As an alternative, non-invasive, and diagnostic pond-monitoring method, we and others are interested in identifying signature chemicals to aid in rapid and accurate identification and/or detection of biological contamination in order to facilitate targeted and effective treatment to save the algal crop from a catastrophic crash. It is well known that deleterious species produce various volatile organic compounds (VOCs) as specific biomarkers of their predatory action [20] and monitoring VOCs in health and disease is similarly underway [21]. Since microalgae and their predators both produce volatile organic compounds (VOCs) throughout their life cycle [22; 23], there is potential that VOCs serve as indicators of unhealthy ponds that may indicate the presence of microalgalpredators. Recently, we have demonstrated feasibility of using VOCs as biomarkers of pond health with _Microchloropysis salina_ in the presence and absence of the marine rotifer, _Brachious plicatilis_[24; 25]. These works used solid-phase microextraction (SPME) or Car-bopack thermal desorption (TD) tubes to non-invasively collect headspace volatiles for analysis by gas chromatography-mass spectrometry (GC-MS). In the present study, we expand upon this work by determining if VOCs generated by the algae undergoing grazing by rotifers are specific for the grazing event or represent a generic chemical signal of algae crop damage. The goal of this study was to determine the difference between the VOCs released from algae upon ingestion by a rotifer, with all the attendant digestive processes, and those released by the physical disruption of the algae alone. Grazing by rotifers was selected as the biotic crash mechanism because they are important threat to production systems with which we have significant experience and have developed standard grazer assays. Among the various abiotic crash mechanisms, freeze than treatment was selected because of the ability to treat the entire algal culture to ensure that the vast majority of cells were disrupted simultaneously. Second, it was not necessary to alter the physiological state for the algal cells (i.e., through nutrient depletion) to achieve physical disruption. That allowed us to match the physiological state of the culture prior to freeze-thaw to that of the culture prior to rotifers addition. In this study we have surveyed and compared the production of VOCs by _M. gaditana_ in the presence and absence of both abiotic and biotic damage. We have identified specific VOC differences for _M. gaditana_ in the presence of rotifer grazing versus healthy cultures. Although several VOCs are the same as produced by _M. salina_ in the presence of actively grazing rotifers [24], we have identified at least one reportable difference. Additionally, we induced the physical disruption of _M. gaditana_ cells through repeated freeze-thaw events which elicited a different array of VOCs, suggesting that different algal crop damaging events might produce specific VOCs that could be used diagnostically and aid in specific interdictive strategies to save a pond from crashing [4]. Resulting chemical fingerprints are potential targets for future chemical monitoring systems (such as micro-GC device, see [26] for review) in microalgal cultivation.