Diel Variations in Cell Abundance and Trophic Transfer of Diarrheic Toxins during a Massive Bloom in Southern Brazil.

spp. are a major source of diarrheic toxins to marine food webs, especially during blooms. This study documented the occurrence, in late May 2016, of a massive toxic bloom of the complex along the southern coast of Brazil, associated with an episode of marked salinity stratification. The study tracked the daily vertical distribution of spp. cells and their ciliate prey, cf. , and quantified the amount of lipophilic toxins present in seston and accumulated by various marine organisms in the food web. The abundance of the complex reached 43 × 10⁴ cells·L at 1.0 m depth at the peak of the bloom. Maximum cell densities of cryptophyceans and cf. (>500 × 10⁴ and 18 × 10⁴ cell·L, respectively) were recorded on the first day of sampling, one week before the peak in abundance of the complex. The diarrheic toxin okadaic acid (OA) was the only toxin detected during the bloom, attaining unprecedented, high concentrations of up to 829 µg·L in seston, and 143 ± 93 pg·cell in individually picked cells of the complex. Suspension-feeders such as the mussel, , and barnacle, , accumulated maximum OA levels (up to 578.4 and 21.9 µg total OA·Kg, respectively) during early bloom stages, whereas predators and detritivores such as Caprellidae amphipods (154.6 µg·Kg), gastropods (111.6 µg·Kg), crabs (33.4 µg·Kg) and a commercially important species of shrimp, (7.2 µg·Kg), only incorporated OA from mid- to late bloom stages. Conjugated forms of OA were dominant (>70%) in most organisms, except in blenny fish, , and polychaetes, (up to 59.3 and 164.6 µg total OA·Kg, respectively), which contained mostly free-OA throughout the bloom. Although algal toxins are only regulated in bivalves during toxic blooms in most countries, including Brazil, this study indicates that human seafood consumers might be exposed to moderate toxin levels from a variety of other vectors during intense toxic outbreaks.