Description: In the Argentine Sea, blooms of toxigenic dinoflagellates of the Alexandrium tamarense species complex have led to fish and bird mortalities and human deaths as a consequence of paralytic shellfish poisoning (PSP). Yet little is known about the occurrence of other toxigenic species of the genus Alexandrium, or of their toxin composition beyond coastal waters. The distribution of Alexandrium species and related toxins in the Argentine Sea was determined by sampling surface waters on an oceanographic expedition during austral spring from ~39°S to 48°S. Light microscope and SEM analysis for species identification and enumeration was supplemented by confirmatory PCR analysis from field samples. The most frequent Alexandrium taxon identified by microscopy corresponded to the classical description of A. tamarense. Only weak signals of Group I from the A. tamarense species complex were detected by PCR of bulk field samples, but phylogenetic reconstruction of rDNA sequences from single cells from one station assigned them to ribotype Group I (Alexandrium catenella). PCR probes for Alexandrium minutum and Alexandrium ostenfeldii yielded a positive signal, although A. minutum morphology did not completely match the classical description. Analysis of PSP toxin composition of plankton samples revealed toxin profiles dominated by gonyautoxins (GTX1/4). The main toxic cyclic imine detected was 13-desMe-spirolide C and this supported the association with A. ostenfeldii in the field. This study represents the first integrated molecular, morphological and toxinological analysis of field populations of the genus Alexandrium in the Argentine Sea.

Description: The marine diatom genus Pseudo-nitzschia, the major known producer of the neurotoxin domoic acid (DA) responsible for the amnesic shellfish poisoning (ASP) syndrome in humans and marine mammals, is globally distributed. The genus presents high species richness in the Argentine Sea and DA has been frequently detected in the last few years in plankton and shellfish samples, but the species identity of the producers remains unclear. In the present work, the distribution and abundance of Pseudo-nitzschia species and DA were determined from samples collected on two oceanographic cruises carried out through the Argentine Sea (∼39–47°S) during summer and spring 2013. Phytoplankton composition was analysed by light and electron microscopy while DA was determined by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The genus Pseudo-nitzschia was recorded in 71 and 86% of samples collected in summer and spring, respectively, whereas DA was detected in only 42 and 21% of samples, respectively. Microscopic analyses revealed at least five potentially toxic species (P. australis, P. brasiliana, P. fraudulenta, P. pungens, P. turgidula), plus putatively non-toxigenic P. dolorosa, P. lineola, P. turgiduloides and unidentified specimens of the P. pseudodelicatissima complex. The species P. australis showed the highest correlation with DA occurrence (r = 0.55; p 〈 0.05), suggesting its importance as a major DA producer in the Argentine Sea. In the northern area and during summer, DA was associated with the presence of P. brasiliana, a species recorded for the first time in the Argentine Sea. By contrast, high concentrations of P. fraudulenta, P. pungens and P. turgidula did not correspond with DA occurrence. This study represents the first successful attempt to link toxigenicity with Pseudo-nitzschia diversity and cell abundance in field plankton populations in the south-western Atlantic.

Description: Dinophysis is a cosmopolitan genus of marine dinoflagellates, considered as the major proximal source of diarrheic shellfish toxins and the only producer of pectenotoxins (PTX). From three oceanographic expeditions carried out during autumn, spring and late summer along the Argentine Sea (∼38–56°S), lipophilic phycotoxins were determined by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) in size-fractionated plankton samples. Lipophilic toxin profiles were associated with species composition by microscopic analyses of toxigenic phytoplankton. Pectenotoxin-2 and PTX-11 were frequently found together with the presence of Dinophysis acuminata and Dinophysis tripos. By contrast, okadaic acid was rarely detected and only in trace concentrations, and dinophysistoxins were not found. The clear predominance of PTX over other lipophilic toxins in Dinophysis species from the Argentine Sea is in accordance with previous results obtained from north Patagonian Gulfs of the Argentine Sea, and from coastal waters of New Zealand, Chile, Denmark and United States. Dinophysis caudata was rarely found and it was confined to the north of the sampling area. Because of low cell densities, neither D. caudata nor Dinophysis norvegica could be biogeographically related to lipophilic toxins in this study. Nevertheless, the current identification of D. norvegica in the southern Argentine Sea is the first record for the southwestern Atlantic Ocean. Given the typical toxigenicity of this species on a global scale, this represents an important finding for future surveillance of plankton-toxin associations.

Description: The marine diatom genus Pseudo-nitzschia, the major known producer of the neurotoxin domoic acid (DA) responsible for the amnesic shellfish poisoning (ASP) syndrome in humans and marine mammals, is globally distributed. The genus presents high species richness in the Argentine Sea and DA has been frequently detected in the last few years in plankton and shellfish samples, but the species identity of the producers remains unclear. In the present work, the distribution and abundance of Pseudo-nitzschia species and DA were determined from samples collected on two oceanographic cruises carried out through the Argentine Sea (∼39–47°S) during summer and spring 2013. Phytoplankton composition was analysed by light and electron microscopy while DA was determined by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The genus Pseudo-nitzschia was recorded in 71 and 86% of samples collected in summer and spring, respectively, whereas DA was detected in only 42 and 21% of samples, respectively. Microscopic analyses revealed at least five potentially toxic species (P. australis, P. brasiliana, P. fraudulenta, P. pungens, P. turgidula), plus putatively non-toxigenic P. dolorosa, P. lineola, P. turgiduloides and unidentified specimens of the P. pseudodelicatissima complex. The species P. australis showed the highest correlation with DA occurrence (r = 0.55; p 〈 0.05), suggesting its importance as a major DA producer in the Argentine Sea. In the northern area and during summer, DA was associated with the presence of P. brasiliana, a species recorded for the first time in the Argentine Sea. By contrast, high concentrations of P. fraudulenta, P. pungens and P. turgidula did not correspond with DA occurrence. This study represents the first successful attempt to link toxigenicity with Pseudo-nitzschia diversity and cell abundance in field plankton populations in the south-western Atlantic.

Description: The marine dinophycean genus Azadinium has been identified as the primary source of azaspiracids (AZA), a group of lipophilic phycotoxins known to accumulate in shellfish. Blooms of Azadinium in the southern Atlantic off Argentina have been described from the 1990s, but due to a lack of cultures, the diversity of South-Atlantic Azadinium has not yet been fully explored and their toxin production potential is completely unknown. During a spring 2010 research cruise covering the El Rinco´n (ER) estuarine system (North Patagonian coast, Argentina, Southwestern Atlantic) a search was conducted for the presence of Azadinium. Although neither Azadinium cells nor AZA in field plankton samples were detected, 10 clonal strains of Azadinium poporum were successfuly established by incubation of sediment samples. Argentinean A. poporum were more variable in size and shape than the type description but conformed to it by the presence of multiple pyrenoids with starch sheath, in plate pattern and arrangement, and in the position of the ventral pore located on the left side of the pore plate. In contrast to all previous description of A. poporum, isolates of the Argentinean A. poporum possessed a distinct field of pores on the second antapical plate. Conspecificity of the Argentinean isolates with A. poporum was confirmed by molecular phylogeny of concatenated ITS and LSU rDNA sequences, where all Argentinean isolates together with some Chinese A. poporum strains formed a well-supported ribotype clade within A. poporum. All isolates produced AZA with the same profile, consisting of AZA-2 as the major compound and, to a lesser extent, its phosphated form. This is the first report of a phosphated marine algal toxin. This first confirmation of the presence of AZA producing Azadinium in the Argentinean coastal area underlines the risk of AZA shellfish contamination episodes in the Southwestern Atlantic region.

Description: The overlay of cooler nutrient enriched Beagle–Magellan water with warmer nutrient depleted shelf water and a strong stratification of the water column in the San Jorge Gulf region, Argentina, coincided with relatively high dinoflagellate abundances in April 2012, up to 34,000 cells L− 1. This dinoflagellate proliferation was dominated by Ceratium spp., but environmental conditions also favored to a lesser amount the occurrence of toxigenic dinoflagellates, such as Alexandrium tamarense and Protoceratium reticulatum, whose toxins were hardly detected in any other areas along the expedition transect of the R/V Puerto Deseado between 38 and 56°S (Ushuaia–Mar del Plata) in March/April 2012. Generally vegetative cells of A. tamarense and P. reticulatum co-occurred with their respective phycotoxins in the water column and their cysts in the upper sediment layers. Two strains of A. tamarense were isolated from the bloom sample and morphologically characterized. Their PSP toxin profiles consisted of C1/2, gonyautoxins 1/4 and to a lesser amount of neosaxitoxin and confirmed earlier data from this region. The ratios between autotrophic picoplankton and heterotrophic bacteria were higher in shelf waters in the north than in Beagle–Magellan waters in the south of San Jorge Gulf.

Description: The species Dinophysis tripos is a widely distributed marine dinoflagellate associated with diarrheic shellfish poisoning (DSP) events, which has been recently identified as a pectenotoxin (PTX) producer. In two sampling expeditions carried out during austral autumns 2012 and 2013 along the Argentine Sea (�38–568 S), lipophilic phycotoxins were measured by tandem mass spectrometry coupled to liquid chromatography (LC–MS/MS) in size-fractionated plankton samples together with microscopic analyses of potentially toxic phytoplankton. PTX-2, PTX-11 and PTX-2sa were recurrently detected in the 50– 200 mm fractions, in association to D. tripos. PTX-2 was also widely distributed among the 20–50 mm fractions, mostly related to Dinophysis acuminata. Okadaic acid or its analogs were not detected in any sample. This is the first report of D. tripos related to PTX in the Argentine Sea and the first record of PTX- 11 and PTX-2sa for this area. The morphological variability of D. tripos, including the presence of intermediate, small and dimorphic cells, is described. Also, the micro- and mesoplanktonic potential grazers of Dinophysis spp. were explored.

Description: Protoceratium reticulatum is a dinoflagellate with a life cycle that includes a motile planktonic stage and a resting cyst stage in benthic habitat, both with a wide geographical distribution, including southern South America. P. reticulatum produces yessotoxins (YTX) – these can be accumulated in shellfish and show potent cytotoxicity, posing a risk to human health if contaminated shellfish is consumed. YTX have been reported from coastal shellfish of many localities, but until now it was unknown if they were present in the austral Southwestern Atlantic and also if local populations of P. reticulatum have the ability to produce these toxins. In this study we report the presence of YTX in plankton samples and its production in culture by two P. reticulatum strains isolated from the San Jorge Gulf (SJG). In addition, we describe the geographical distribution and seasonal abundance of this species based on data collected over the past two decades. The YTX cell quotas calculated from net hauls (∼10 pg cell−1) are in the same range as the toxin cell quotas observed in these two isolates. The phylogenetic analysis of sequences of the hypervariable region of the large subunit (LSU) 28S rDNA showed that the two clonal strains from the SJG were part of a monophyletic clade that subdivides P. reticulatum into two well-supported, divergent sub-clades. The sequences of the two strains of P. reticulatum from the SJG fell in the same clade as the majority of sequences of P. reticulatum, which belong to a geographically widely distributed evolutionary clade. P. reticulatum was occasionally observed from about 35° S in Uruguayan shelf waters up to 53° S on the Patagonian shelf and north of Tierra del Fuego, and it was present from coastal areas up to the shelf break zone. We recorded P. reticulatum in plankton samples during spring, summer and autumn but invariably in low abundance (maximum: 560 cells L−1). Viable cysts of the species in surface sediments also showed a wide geographical distribution. Together, the high total abundances and high relative numerical contribution to planktonic dinoflagellate assemblages near frontal areas, emphasize the necessity to pay attention to the dynamics of this species in areas of potential risk of harmful algal bloom development.