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Abstract Much of the evolutionary ecology of toxic algal blooms (TABs) remains unclear, including the role of algal toxins in the adaptive ‘strategies’ of TAB‐forming species. Most eukaryotic TABs are caused by mixotrophs that augment autotrophy with organic nutrient sources, including competing algae (intraguild predation). We leverage the standing diversity of TABs formed by the toxic, invasive mixotrophPrymnesium parvumto identify cell‐level behaviours involved in toxin‐assisted predation using direct observations as well as comparisons between genetically distinct low‐ and high‐toxicity isolates. Our results suggest thatP. parvumtoxins are primarily delivered at close range and promote subsequent prey capture/consumption. Surprisingly, we findoppositechemotactic preferences for organic (prey‐derived) and inorganic nutrients between differentially toxic isolates, respectively, suggesting behavioural integration of toxicity and phagotrophy. Variation in toxicity may, therefore, reflect broader phenotypic integration of key traits that ultimately contribute to the remarkable flexibility, diversity, and success of invasive populations.