The cultivation and downstream processing of microalgal biomass for low to medium value products has high associated costs (Uduman et al., 2010), and despite the emergence of new technologies and efforts to increase efficiencies, significant improvements for large-scale production are still required. Open raceway ponds represent the cheapest method of large-scale microalgae production, requiring only low power inputs and relatively simple maintenance (Vieira Costa et al., 2014). However, these systems still experience numerous limitations such as contamination risks from undesirable organisms, i.e. grazers, which could potentially damage the entire algal cultivation (Montemezzani et al., 2015). Also, commercialisation of a variety of algal bioproducts is still limited, namely due to high operating costs in downstream processing, with the most crucial and expensive step being dewatering and biomass harvesting, accounting for up to 30% of the overall production cost (Uduman et al., 2010, Vandamme et al., 2013). Chemical cues released by grazers like Daphnia and known as infochemicals can induce defensive responses in microalgae, including colony formation, flocculation and other morphological changes (Hessen & van Donk, 1993, Lampert et al., 1994, Lürling & van Donk, 1996, Lürling, 2003). This thesis investigates this phenomenon, as a process which could be exploited within biotechnology to facilitate flocculation of algal cells and therefore harvesting. More specifically, the focus is on the green alga Scenedesmus subspicatus and the zooplanktonic organism Daphnia magna, which act as exemplar organisms.