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Abstract 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. 

SeveralDinophysisspecies produce lipophilic toxins (diarrhetic shellfish poisoning, DSP and pectenotoxins PTX) which are transferred through the food web. Even at low cell densities (< 10³cell L^-1), they can cause human illness and shellfish harvesting bans; toxins released into the water may kill early life stages of marine organisms.Dinophysisspecies are mixotrophs: they combine phototrophy (by means of kleptoplastids stolen from their prey) with highly selective phagotrophy on the ciliateMesodinium, also a mixotroph which requires cryptophyte prey of theTeleaulax/Geminigeraclade. Life cycle strategies, biological interactions and plastid acquisition and functioning inDinophysisspecies make them exemplars of resilient holoplanktonic mixoplankters and of ongoing speciation and plastidial evolution. Nevertheless, 17 years after the first successful culture was established, the difficulties in isolating and establishing cultures with local ciliate prey, the lack of robust molecular markers for species discrimination, and the patchy distribution of low-density populations in thin layers, hinder physiological experiments to obtain biological measurements of their populations and slow down potential advances with next-generation technologies. The Omic’s age inDinophysisresearch has only just started, but increased efforts need to be invested in systematic studies of plastidic diversity and culture establishment of ciliate and cryptophyte co-occurring withDinophysisin the same planktonic assemblages. 

At the end of summer 2020, a moderate (~105 cells L−1) bloom of potential fish-killing Karenia spp. was detected in samples from a 24 h study focused on Dinophysis spp. in the outer reaches of the Pitipalena-Añihue Marine Protected Area. Previous Karenia events with devastating effects on caged salmon and the wild fauna of Chilean Patagonia had been restricted to offshore waters, eventually reaching the southern coasts of Chiloé Island through the channel connecting the Chiloé Inland Sea to the Pacific Ocean. This event occurred at the onset of the COVID-19 lockdown when monitoring activities were slackened. A few salmon mortalities were related to other fish-killing species (e.g., Margalefidinium polykrikoides). As in the major Karenia event in 1999, the austral summer of 2020 was characterised by negative anomalies in rainfall and river outflow and a severe drought in March. Karenia spp. appeared to have been advected in a warm (14–15 °C) surface layer of estuarine saline water (S > 21). A lack of daily vertical migration patterns and cells dispersed through the whole water column suggested a declining population. Satellite images confirmed the decline, but gave evidence of dynamic multifrontal patterns of temperature and chl a distribution. A conceptual circulation model is proposed to explain the hypothetical retention of the Karenia bloom by a coastally generated eddy coupled with the semidiurnal tides at the mouth of Pitipalena Fjord. Thermal fronts generated by (topographically induced) upwelling around the Tic Toc Seamount are proposed as hot spots for the accumulation of swimming dinoflagellates in summer in the southern Chiloé Inland Sea. The results here provide helpful information on the environmental conditions and water column structure favouring Karenia occurrence. Thermohaline properties in the surface layer in summer can be used to develop a risk index (positive if the EFW layer is thin or absent).