Spatial distribution of Pseudo-nitzschia (Bacillariophyceae) species in shelf and oceanic waters of the South Western Atlantic

ALDER, V.A.; OLGUÍN SALINAS HF

Auckland

Simposio; XXXIII SCAR BIENNAL MEETING; 2014

SCAR

Some diatom species belonging to the genus Pseudo-nitzschia are potential producers of domoic acid, a neurotoxin which causes amnesic shellfish poisoning (ASP). Despite the harmful effect that these species may have on marine food webs and human health, no previous studies have addressed their abundance and distribution covering a large spatial scale in the oceanic waters of South Western Atlantic. The present study is based on the analysis of 116 samples collected from 34°S to 76°S during different surveys conducted in the outer Argentine shelf, the Brazil-Malvinas Confluence, Drake Passage, Antarctic Peninsula, and Weddell Sea during austral spring and/or summer. Diatom densities were estimated by cell counting under an inverted microscope, while species identification was carried out after the oxidation of organic material, drying on cover glasses and mounting in a refractive medium. The genus Pseudo-nitzschia showed a mean concentration of 186 cells l-1 and occurred in 96% of the stations. A total of 14 species of Pseudo-nitzschia were recorded, four of which reached concentrations up to 104 cells l-1 (P. lineola, P. turgiduloides, P. prolongatoides y P. subcurvata). The former three were particularly abundant in ice-free waters of the SE Weddell Sea, while the latter peaked around the tip of Antarctic Peninsula. Seven other species identified (P. multiseries, P. australis, P. pungens, P. turgidula, P. fraudulenta, P. delicatissima complex, and P. cf. calliantha) are commonly regarded as potential producers of domoic acid. An ecological characterization (excluding the Weddell Sea) based on Pseudo-nitzschia species abundance and environmental variables (nitrates, phosphates, silicates, temperature, and depth) was carried out through a Canonical Redundancy Analysis. Among other results, we found that: a) the Brazil-Malvinas Confluence can be differentiated by the presence of P. multiseries (major load), P. fraudulenta, P. subfraudulenta, and P. cf calliantha; b) subantarctic oceanic waters and the Drake Passage host a high load of P. lineola, P. heimii, P. turgiduloides, and P. turgidula; c) the Argentine shelf and slope, and the waters surrounding the Antarctic Peninsula are characterized by the dominance of P. lineola and P. turgiduloides, with lesser concentrations of P. subcurvata and P. pungens.