Prey morphotype and abundance controls plastid retention and bloom dynamics for a mixotrophic dinoflagellate

Dinophysis is an obligate mixotroph that relies on consumption of the ciliate, Mesodinium rubrum, to grow and form harmful algal blooms (HABs). In this study, blooms of Dinophysis acuminata in two NY, USA, estuaries were studied over the course of 3 yr (2019–2021) using discrete samples and an Imaging FlowCytobot (IFCB) to capture images of plankton 20–150 μm. The darkness of Dinophysis images on the IFCB was used to quantify the “fullness” or feeding state of Dinophysis cells. Culture experiments performed to ground truth this approach revealed a highly significant correlation (R = 0.98; p