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Background and aims: Planktonic dinoflagellates have a great ecological significance in marine environments. While some dinoflagellate species commonly reach bloom concentrations and are thus conspicuous components of marine phytoplankton, others occur in very low abundances which make them difficult to detect in field studies.Here we analyzed dinoflagellate composition and abundance in five oceanographic expeditions carried out in continental shelf and slope waters of the Argentine Sea.M&M: Plankton abundance was estimated by the Utermöhl method, using inverted microscopy, whereas further optical and scanning electron microscopy was applied for the identification of dinoflagellate species.Results: We focused on the occurrence of seven dinoflagellates that have been previously poorly documented or overlooked in marine environments worldwide: Dinophysis microstrigiliformis; Gyrodinium sp.; Karlodinium elegans; Oxytoxumlaticeps; Peridiniella danica; Peridiniella globosa and Prorocentrum nux. The latest and K. elegans are observed for the first time in field conditions after their original descriptions based on cell cultures. While most species were detected in low ormoderate abundances, P. nux, which is the smallest Prorocentrum species, reached 82,000 cells L-1 in slope waters. Very small Gyrodinium cells (11.5 µm long; 8.7 µm wide) with a distribution restricted to slope waters during spring, were not possible tobe accurately assigned to a species.Conclusions: This study contributes to the understanding of dinoflagellate diversity in the Argentine Sea and the worldwide distribution of little known species.

Plankton composition and density, and domoic acid (DA) content in microplankton and mesozooplankton were assessed over the northern Patagonian coastal shelf in late austral summer 2013. Maximum values of DA in these two plankton fractions as well as maximum densities of both Pseudo-nitzschia spp. (mainly the toxigenic P. australis) and DA potential vectors were only detected on the southern coast of San Matías Gulf and the eastern coast of Valdés Peninsula. In this zone, waters were characterized by low temperature, high nitrate, and intermediate values of silicic acid and phosphate. Based on the high association between the DA values recorded and the values of either micro- and mesozooplankton grazer density or biomass, we inferred that DA transfer from Pseudo-nitzschia spp. occurred largely through the small copepods Euterpina acutifrons and Oithona nana, Calanidae nauplii and Calanidae copepodites, Noctiluca scintillans, and euphausiid developmental stages. Small copepods, Calanidae nauplii and copepodites, and cladocerans were proposed as novel DA vectors although this suggestion requires experimental confirmation. This study provides the first lines of evidence of the co-occurrence of Pseudo-nitzschia spp. blooms with DA production and accumulation in mesozooplanktonic grazers at the base of the food web and of the environmental and oceanographic conditions that seem to favor these processes over the northern Patagonian shelf coasts.

Some dinoflagellate species of the genera Azadinium and Amphidoma (Amphidomataceae) produce azaspiracids (AZA), a group of toxins responsible for gastrointestinal disorders in humans following the consumption of contaminated shellfish. In this study, we investigated the diversity, distribution and abundance of Azadinium and AZA from field plankton samples collected during four oceanographic expeditions that covered an extended area of the Argentine Sea during different seasons. Scanning electron microscopy analyses indicated the presence of five Azadinium species: Az. dexteroporum, Az. luciferelloides, Az. obesum, Az. asperum and Az. cf. poporum. Azadinium-like cells were frequently found and were even an abundant component of plankton assemblages, showing a wide latitudinal distribution, from ~38 to ~55.5°S, and occurring in a wide temperature and salinity range. High cell densities (up to 154000cellsL⁻¹) occurred in northern slope and external shelf waters during spring. AZA-2 was detected in net samples from the 20- to 200-µm fractions by tandem mass spectrometry–liquid chromatography analysis, suggesting a transfer of AZA through the food web. Our results contribute to the knowledge of the worldwide occurrence of Azadinium species and AZA, and highlight the importance of amphidomatacean species as a potential source of AZA shellfish poisoning in the south-west Atlantic Ocean., Facultad de Ciencias Naturales y Museo

Las yessotoxinas (YTXs) son un grupo de ficotoxinas descrito recientemente, asociado a toxicidad en moluscos y a cardiotoxicidad en ratones de laboratorio. Hasta el momento se conocen tres especies de dinoflagelados productoras de YTXs a nivel mundial: Protoceratium reticulatum, Gonyaulax spinifera y Lingulodinium polyedra. En este estudio se analizó la presencia de YTXs y de sus potenciales productores en cuatro campañas oceanográficas realizadas en diferentes estaciones del año entre los 38 y 55ºS. La detección de toxinas se realizó mediante cromatografía líquida de alta eficiencia acoplada con espectrometría de masas en tándem. Los análisis morfológicos incluyeron observaciones mediante microscopía óptica y electrónica de barrido. Se encontraron dos potenciales productores de YTXs, Protoceratium reticulatum y Gonyaulax spinifera, presentando densidades máximas de 660 y 140 cél. L-1 respectivamente durante las campañas de otoño y primavera, en las cuales se detectó YTX en muestras del Golfo San Jorge y del talud. Los datos obtenidos sugieren que la especie P. reticulatum es la principal productora de YTXs en el Mar Argentino presentando cuotas celulares entre 2,2 y 12,5 pg YTX cél.-1, mientras que G. spinifera representa un productor potencial en la región que no ha mostrado una asociación clara con la detección de YTX. Dinoflagellates producers of yessotoxins in the Argentine Sea. Yessotoxins (YTXs) consist of a recently described group of phycotoxins associated with shellfish toxicity and with cardiotoxicity in laboratory rodents. Until now there are only three dinoflagellate species considered as YTXs producers: Protoceratium reticulatum, Gonyaulax spinifera and Lingulodinium polyedra. In this study the presence of YTX and its potential producers in the Argentine Sea was analyzed by four oceanographic expeditions carried out between 38 and 55ºS and during different seasons. Toxin detection was performed by application of liquid chromatography coupled to tandem mass spectrometry. Morphological analysis included optical and scanning electron microscopy. Two YTXs potential producers were found: Protoceratium reticulatum and Gonyaulax spinifera, showing highest concentrations of 660 and 140 cell L-1 respectively, during autumn and spring. YTX were also detected during autumn and spring in samples from San Jorge Gulf and slope waters and were associated with the presence of P. reticulatum, showing toxin cell quotas of 2.2 and 12.5 pg YTX cell-1. The data obtained suggest that P. reticulatum is the main YTXs producer in the Argentine Sea, while G. spinifera represents a potential producer in the region which did not show a clear association with YTX detection. Fil: Fabro Cerreia Fus, Elena Ines. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina Fil: Krock, Bernd. Alfred-Wegener-Institut. Helmholtz-Zentrum für Polar und Meeresforschung; Alemania Fil: Almandoz, Gaston Osvaldo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina

The recently established diatom genus Shionodiscus is characterized as possessing a labiate process on the valve face and strutted processes with long internal and reduced, or no, external extensions. Many Thalassiosira species with these features were transferred to this new genus, as well as some with short internal, strutted process extensions. Examination of samples from the Argentine continental shelf and slope waters, and from the Beagle Channel, revealed the presence of a small centric diatom that formed an extensive bloom in slope waters during spring 2005 and 2006. Analysis by light and electron microscopy revealed high similarity to specimens previously referred as Thalassiosira bioculata var. raripora. This name was never effectively published; nevertheless, the name has been adopted and observations referring to it have been reported on several occasions. Here we trace the usage of the (nomenclaturally invalid) name Thalassiosira bioculata var. raripora in the literature, and formally describe the species as Shionodiscus gaarderae, based on our observations and comparison with previous reports. A morphological comparison of this and similar taxa is also provided. In addition, we offer an emended description of S. bioculatus var. bioculatus from Ostenfeld material sampled from the ‘Färöer Island Naströ Fjord Plankton (16.9.1902)’, held in the Hustedt collection. Finally, we propose the transfer of Thalassiosira rosulata to Shionodiscus. Fil: Ferrario, Martha Elba. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina Fil: Almandoz, Gaston Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina Fil: Cefarelli, Adrián Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Desarrollo Costero; Argentina Fil: Beszteri, Bank. Helmholtz-Zentrum für Polar- und Meeresforschung. Alfred-Wegener-Institut; Alemania Fil: Akselman Cardella, Rut. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Subsede Instituto Nacional de Investigación y Desarrollo Pesquero; Argentina Fil: Fabro Cerreia Fus, Elena Ines. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina Fil: Cembella, Allan. Helmholtz-Zentrum für Polar- und Meeresforschung. Alfred-Wegener-Institut; Alemania

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. Fil: Fabro Cerreia Fus, Elena Ines. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Almandoz, Gaston Osvaldo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Ferrario, Martha Elba. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: John, Uwe. Alfred Wegener Institut-Helmholtz Zentrum fur Polar und Meeresforschung; Alemania Fil: Tillmann, Urban. Alfred Wegener Institut-Helmholtz Zentrum fur Polar und Meeresforschung; Alemania Fil: Toebe, Kerstin. Alfred Wegener Institut-Helmholtz Zentrum fur Polar und Meeresforschung; Alemania Fil: Krock, Bernd. Alfred Wegener Institut-Helmholtz Zentrum fur Polar und Meeresforschung; Alemania Fil: Cembella, Allan. Alfred Wegener Institut-Helmholtz Zentrum fur Polar und Meeresforschung; Alemania

The Beagle Channel is a remote subantarctic environment where mussel aquaculture initiatives have existedsince the early 1990s. Here we analyze phytoplankton biomass and composition, and the occurrence of harmfulmicroalgae species and their toxins at three sites during the period 2015?2016. The occurrence of potentiallyharmful algae was observed throughout the study period, including toxigenic dinoflagellates such asAlexandrium catenella (Group I of the A. tamarense complex), A. ostenfeldii, Dinophysis acuminata, Gonyaulaxspinifera, Azadinium sp., and the diatoms Pseudo-nitzschia australis and P. fraudulenta. Toxic dinoflagellates weredetected in low densities whereas a Pseudo-nitzschia bloom was observed in late February. Isolates of A. catenellaand P. delicatissima sensu stricto were phylogenetically characterized. The toxin profile of A. catenella wasdominated by GTX4, while P. delicatissima sensu stricto showed no production of the neurotoxin domoic acid inculture conditions. The results provide base-line information for the management of harmful algal blooms in thislittle explored subantarctic area. Fil: Almandoz, Gaston Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina Fil: Cefarelli, Adrián Oscar. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro de Investigaciones y Transferencia Golfo San Jorge. Centro de Investigaciones y Transferencia Golfo San Jorge: Sede Caleta Olivia - Santa Cruz | Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia Golfo San Jorge. Centro de Investigaciones y Transferencia Golfo San Jorge: Sede Caleta Olivia - Santa Cruz | Universidad Nacional de la Patagonia "san Juan Bosco". Centro de Investigaciones y Transferencia Golfo San Jorge. Centro de Investigaciones y Transferencia Golfo San Jorge: Sede Caleta Olivia - Santa Cruz; Argentina. Universidad Nacional de la Patagonia "San Juan Bosco". Instituto de Desarrollo Costero; Argentina Fil: Diodato, Soledad Lorena. Universidad Nacional de Tierra del Fuego, Antártida e Islas del Atlántico Sur. Instituto de Ciencias Polares, Ambientales y Recursos Naturales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina Fil: Montoya, Nora Gladys. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina Fil: Benavides, Hugo R.. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina Fil: Carignan, Mario Osvaldo. Instituto Nacional de Investigaciones y Desarrollo Pesquero; Argentina Fil: Hernando, Marcelo Pablo. Comisión Nacional de Energía Atómica; Argentina Fil: Fabro Cerreia Fus, Elena Ines. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina Fil: Metfies, Katja. Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung; Alemania Fil: Lundholm, Nina. Universidad de Copenhagen; Dinamarca Fil: Schloss, Irene Ruth. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Austral de Investigaciones Científicas; Argentina. Universidad Nacional de Tierra del Fuego; Argentina. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina Fil: Álvarez, Marcela. Instituto Nacional de Investigaciones y Desarrollo Pesquero. Dirección de Pesquerías Demersales. Programa Pesquerías de Peces Demersales Costeros; Argentina Fil: Ferrario, Martha Elba. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Ficología; Argentina

In order to assess the relevance of sporadic upwelling events on primary productivity, the availability of nitrogen (N) sources and their uptake by phytoplankton were studied. Incubations of 15N-enriched samples were performed at 3 depths in 12 stations in San Jorge Gulf (SJG, Patagonia Argentina) aboard of the R/V “Puerto Deseado” during November 2016. Additional coastal stations were sampled to analyze the upwelling event. The total uptake of N sources (ρNO3- + ρNH4+) was higher on the surface than in the deep layer. The ρNO3- by phytoplankton doubled that of ρNH4+ suggesting SJG acted as a CO2 sink during the period studied. However, NH4+ played an important role in maintaining primary productivity where NO3− was low. In most stations, phytoplankton showed a preference for the uptake of the less available N source, likely resulting from adaptation to low nutrient concentrations. However, in the southwestern sector of the gulf, where a wind-induced upwelling occurred, phytoplankton preferred to uptake NO3−, this being the most abundant N source. As a consequence, the integrated primary productivity in the water column of that sector was high. Results suggest that such high productivity was governed by the optimal relationship between the preference and availability of N, established by the presence of elevated NO3− and low NH4+ ambient concentration. This would be a physiological process regardless of community composition. The new primary productivity generated by upwelling events could be key to feeding the biological resources of the gulf.

The present work reports the first data set on particulate organic carbon (POC) and nitrogen (PON), and the high-resolution modelling of their stable isotope variability in the Patagonian Cold Estuarine System (PCES), with focus on particulate organic matter (POM) origin and distribution in dependence on physical, chemical and biological parameters. POC, PON, stable carbon (δ¹³C) and nitrogen isotopes (δ¹⁵N), dissolved organic nitrogen, phaeopigments, diatom, dinoflagellate and heterotrophic bacteria (HB) abundance are reported for 17 stations in different waters masses in the southern end of the Argentine shelf in late summer 2012. Most parameters denote clear differences between Beagle - Magellan Water (BMW), Subantarctic Shelf Water (SSW) and Subantarctic Water (SAW). POC and PON decreased from maxima in BMW to intermediate values in SSW and minima in SAW. There was a highly significant correlation among POC, PON and fluorescence indicators of diagenetic maturity of dissolved humic matter. This, together with the inverse correlations of salinity with POC and PON, and the wide range of C:N ratios indicate that POM in the study area is partly derived from terrestrial runoff, superimposed by autochthonous components from plankton of different life stages. HB abundance was significantly correlated with POC and dissolved organic matter (DOM), likely reflecting a resource control of HB and a significant contribution of bacterial biomass to POM in the nanoparticle fraction. The direct relationship between HB and dissolved humics suggests bacterial uptake of DOM fractions otherwise considered refractory. POM complexity was reflected in a wide variation of δ¹³C, despite the narrow temperature range of this region. The variability of stable isotopes of POC could be accounted for by a model with a degree of detail hitherto not reported in the literature. A multiple regression including C:N ratio, ammonium and the quotient between log abundance of diatoms, dinoflagellates and HB explained 92% of δ¹³C variance, mostly produced by ammonium. Despite the strong effect of ammonium on δ¹³C, δ¹⁵N variability was largely explained by a strong inverse relationship with the fraction of unutilized nitrate, suggesting dominance of nitrate uptake. However, the proportion of presumably isotopically heavier ammonium derived from continental runoff in the marine δ¹⁵N-POM pool is unknown and requires investigation of the isotopic composition of dissolved inorganic nitrogen in the PCES. The presented new information and its comparison with data from other sectors of the Argentine shelf constitute a contribution to an approach for the understanding of the organic matter dynamics that can be potentially expanded to the entire Southwest Atlantic., Facultad de Ciencias Naturales y Museo

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 (⁓39–47ºS) 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., Facultad de Ciencias Naturales y Museo

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., Facultad de Ciencias Naturales y Museo

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. Fil: Krock, Bernd. Alfred Wegener Institut-Helmholtz Zentrum für Polar- und Meeresforschung; Alemania Fil: Borel, Claudia Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Geológico del Sur; Argentina Fil: Barrera, Facundo Matías. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina Fil: Tillmann, Urban. Alfred Wegener Institut-Helmholtz Zentrum für Polar- und Meeresforschung; Alemania Fil: Fabro Cerreia Fus, Elena Ines. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Almandoz, Gaston Osvaldo. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Ferrario, Martha Elba. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Garzon Cardona, John Edison. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina Fil: Koch, Boris P.. Alfred Wegener Institut-Helmholtz Zentrum für Polar- und Meeresforschung; Alemania. University of Applied Sciences; Alemania Fil: Alonso, Cecilia. Universidad de la Republica; Uruguay Fil: Lara, Ruben Jose . Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Argentino de Oceanografía (i); Argentina

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 (≈38–56° 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 μm fractions, in association to D. tripos. PTX-2 was also widely distributed among the 20–50 μm 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., Facultad de Ciencias Naturales y Museo