Mesodinium-Dinophysis encounters: temporal and spatial constraints on Dinophysis blooms.

Species of the Dinophysis acuminata complex are the main cause of diarrhetic shellfish poisoning worldwide. These mixotrophs perform photosynthesis with plastids stolen from specific ciliate prey. Current transport models forecast advection of established populations, but modelling bloom development and maintenance also needs to consider the prey (Mesodinium spp.) of Dinophysis. Predator and prey have distinct niches, and Dinophysis bloom success relies on matching prey populations in time and place. During autumn 2019, red tides of Mesodinium rubrum in Reloncaví Fjord, Chile, were not followed by Dinophysis growth. The dynamics of Mesodinium-Dinophysis encounters during this and additional multiscale cases elsewhere are examined. Analogies with some classic predator-prey models (match-mismatch hypothesis; Lasker's stable ocean hypothesis) are explored. Preceding dense populations of Mesodinium do not guarantee Dinophysis blooms if spatial co-occurrence is not accompanied by water column structure, which leads to thin layer formation, as in Lasker's stable ocean hypothesis or if the predator growth season is over. Tracking the frequency of vacuolate Dinophysis cells, irrefutable signal of prey acquisition, with advanced in situ fluid-imaging instruments, is envisaged as a next-generation tool to predict rising Dinophysis populations.