Abstract
The extensive Argentine continental shelf supports high plankton productivity and fish catches. In particular, El Rincon coastal area and the adjacent shelf fronts (38.5–42o S, 58.5–62o W) comprise diverse habitats and hold species of economic and ecological value. So far, studies of the microbial community at the base of the food web remain scarce. Here we describe the early spring plankton (>5-200 µm) structure in terms of abundance, biomass, species composition, functional groups and phycotoxin profiles in surface waters of El Rincon in September 2015. Diatoms were the most abundant and the largest contributors to carbon biomass at most stations. They dominated in coastal and inner-shelf (depths 20 µm) heterotrophic protists, e.g. various ciliates and dinoflagellates species were more abundant offshore. Scanning of phycotoxins in the field disclosed that paralytic shellfish poisoning (PSP) toxins were dominated by gonyautoxins-1/4 (GTX1/4). Lipophilic toxins were detected in low abundance, e.g. domoic acid (DA), although a bloom of Pseudo-nitzschia spp. (up to 3.6 x 105 cells L-1) was detected at inner-shelf stations. Pectenotoxin-2 (PTX-2) and 13-desmethyl spirolide C (SPX-1) were the most abundant in the field. PTX-2 co-occurred with Dinophysis spp., mainly D. tripos, while SPX-1 dominated at middle-shelf stations, where cells of Alexandrium catenella (1 strain) and A. ostenfeldii (3 strains) were isolated. The quantitative PSP profiles of the Alexandrium strains differed significantly from the field profiles. Moreover, the three A. ostenfeldii strains proved to be PSP producers and additionally produced 5 novel spirolides. Phylogenetic analyses of these first strains from the South Atlantic disclosed a new ribotype group suggesting a biogeographical distinction of the population. The plankton survey presented here contributes with baseline knowledge to evaluate potential ecosystem changes and to track the global distribution of toxigenic species.
Highlights
Shelf seas play a major role in ocean carbon cycling and budget, as a large part of the global marine primary production takes place in the coastal areas, and about half of this organic carbon is exported to the deep ocean (Liu et al, 2010)
Sea Surface Temperature (SST), Salinity, and Chlorophyll a Surface temperature was measured in situ in the coastal, innershelf (21 stations with depth
The variability of hydrographic conditions in El Rincón has been ascribed to the seasonal influence of water mass currents along the shelf and shelf breakfronts, river discharges into the shallow area, and anthropogenic activities along the coastline (e.g., Lucas et al, 2005; Palma et al, 2008)
Summary
Shelf seas play a major role in ocean carbon cycling and budget, as a large part of the global marine primary production takes place in the coastal areas, and about half of this organic carbon is exported to the deep ocean (Liu et al, 2010). El Rincón ecosystem, with its middle-shelf front (located at ∼100 m isobaths, Romero et al, 2006), embraces large habitat heterogeneity (Lucas et al, 2005; Palma et al, 2008) characterized by high zooplankton and fish biodiversity (e.g., Marrari et al, 2004; López Cazorla et al, 2014; Acha et al, 2018). Harmful algal blooms (HABs) have been documented in the Argentine shelf for the last 30 years, mainly associated with paralytic shellfish toxins (PSTs) produced by dinoflagellates of the genus Alexandrium (Carreto et al, 1981, 2001; Montoya et al, 2010; Almandoz et al, 2014; Fabro et al, 2017). Particular interest is focused on the species of the dinoflagellate, Alexandrium, isolated at the middle-shelf, as this genus is of major concern due to its tendency to form HABs and its global biogeographical distribution (Anderson et al, 2012)
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