Co-occurrence bloom of lipophilic toxic-producers in a hotspot Chilean fjord: Fine-scale distribution, toxins and fate in shellfish

During the austral summer of 2019, an intense co-occurring bloom of three lipophilic toxin-producing dinoflagellates—Dinophysis acuta, D. acuminata, and Protoceratium reticulatum—was recorded in Puyuhuapi Fjord, a strongly stratified system in northwest Patagonia, Chile. This study investigated the fine-scale vertical distribution of these three toxic species, their associated lipophilic toxins in plankton, and their accumulation in commercially important shellfish.

Using hydrographic profiling, microphytoplankton analysis, UHPLC-MS/MS toxin quantification, and numerical modeling of circulation, we characterized the physical and biological interactions that promote toxin accumulation. The results showed distinct ecological niches for each species and toxin congruent with the stratified water column, with the highest cell and toxin concentrations occurring in thin layers near the head of the Magdalena Sound. Okadaic acid (OA), dinophysistoxin-1 (DTX-1), pectenotoxin-2sa (PTX-2sa), and yessotoxins (YTX) reached peak values in Mytilus chilensis and Aulacomya atra, far exceeding regulatory thresholds.

The spatial distribution of toxins in plankton and shellfish mirrored the physical structure of the fjord, with accumulation linked to weak vertical mixing and high water residence time. These findings highlight species-specific toxin profiles and accumulation potential among filter-feeding bivalves, with implications for seafood safety and sustainability of aquaculture. This study underscores the need to incorporate local hydrographic dynamics into early warning systems for harmful algal blooms (HABs) and supports the development of predictive models for managing toxin outbreaks in vulnerable fjord ecosystems under climate change scenarios.