Phytoplankton (Diatoms and Silicoflagellates) from the Southwestern Atlantic Ocean

Abstract

Diatoms and silicoflageilates from netplankton collected in July 1982 off the Uruguayan and south Brazilian coasts comprised warm-water, cold-water and cosmopolitan forms. Similarity among samples (Sorensen's index) yielded consistently high figures: 0.55 to 0.87 (diatoms), and 0.57 to 1 (silicoflageilates), suggesting that the area is homogeneous from the biogeographical point of view. Sixty-one diatoms and four silicoflagellates comprise the typical winter assemblage for the zone investigated. Cosmopolitan and temperate forms, diatoms: Rhizosolenia setigera, Thalassiosira rotula, Thalassionema nitzschioides and silicoflageilates: Dictyocha fibula, D. speculum, were numerically dominant. Neritic diatoms comprised 45% of the entire inventory, while oceanic ones amounted to 16%. The remaining 39% included organisms which dwell in both types of water. Specific diversity of diatoms was high: Shannon-Weaver's values ranged between 3.4 and 4.6; for silicoflageilates the values were 0.6 to 1.5. These figures are comparable to Central Pacific phytoplanktonic diversity (diatoms, dinoflagellates, coccolithophorids and flagellates pooled), and are 3.7 to 5.7 times higher than diatom diversities recorded for the Subantarctic and Antarctic zones of the Pacific Ocean, respectively. The high diatom diversity observed in the area under study is interpreted as a result of expatriation of subantarctic and subtropical species by the Malvinas Current and Brazil Current, respectively, and to advection of brackish-water taxa due to the influence of the Rio de la Plata outflow.

Description of toxigenic species of the genus Pseudo-nitzschia in coastal waters of Uruguay: Morphology and distribution

“…According to the literature, several species of Pseudo-nitzschia have been recorded for this area: P. australis (Lange and Mostajo, 1985), P. delicatissima (Machado, 1976;Ferrari, 2009), P. fraudulenta (Mé ndez unpubl. ), P. pungens (Negri and Inza, 1998), P. multiseries (Medina et al, 2003), and P. multistriata (Mé ndez and Ferrario, 2009).…”

Morphology and ecology of Thalassiosira Cleve (Bacillariophyta) species rarely recorded in Brazilian coastal waters

“…Of the six Thalassiosira species, only T. hendeyi and T. minuscula were previously reported in the southernmost Brazilian shelf slope, on the Uruguayan border (Lange and Mostajo, 1985). T. hendeyi was also reported in northern Brazil (Franco, 1991), and Ribeiro (1996) recorded T. cf.…”

“…Three studies only include scanning electron microscopy (SEM) microphotographs (Ribeiro, 1996;Torgan and Santos 2006;2007). The highest number of Thalassiosira species was found in the southern Brazilian shelf and slope waters near the boarder with Uruguay (38° 12' S and 57° 15' W-39° 59' S, 54° 11' W; 22 species, Lange and Mostajo, 1985) and along the coast of Paraná State (25° 20'-25° 55' S and 48° 10' S-48° 35' W; 24 species, Procopiak et al, 2006). This study aims to describe and give a full set of illustrations of six Thalassiosira species to date rarely recorded or unrecorded in Brazilian waters.…”

Marine Life of Uruguay: Critical Update and Priorities for Future Research

“…In addition to the taxonomic stud-ies of microplankton and phytoplankton groups (Müller-Melchers 1959, Balech & Souto 1980a, b, Akselman 1985, Lange & Mostajo 1985, a limited number of investigations have dealt with the relation between community structure and environmental conditions (Elgue et al 1987, 1990, Negri et al 1988, Mesones 1991, Gayoso 1996, Gayoso & Podestá 1996. The distribution of the phytoplankton assemblage off the RdlP follows a zonation pattern that reflects the mixing of water masses with differing nutrient contents along a coast-ocean gradient (Negri et al 1988): an estuarine-influenced community immediately offshore from the RdlP is followed by coastal, transition, and subantarctic assemblages.…”