maria Hozbor

The bacterioplankton diversity of coastal waters along a latitudinal gradient between Puerto Rico and Argentina was analyzed using a total of 134,197 high-quality sequences from the V6 hypervariable region of the small-subunit ribosomal RNA gene (16S rRNA) (mean length of 60 nt). Most of the OTUs were identified into Proteobacteria, Bacteriodetes, Cyanobacteria, and Actinobacteria, corresponding to approx. 80% of the total number of sequences. The number of OTUs corresponding to species varied between 937 and 1946 in the seven locations. Proteobacteria appeared at high frequency in the seven locations. An enrichment of Cyanobacteria was observed in Puerto Rico, whereas an enrichment of Bacteroidetes was detected in the Argentinian shelf and Uruguayan coastal lagoons. The highest number of sequences of Actinobacteria and Acidobacteria were obtained in the Amazon estuary mouth. The rarefaction curves and Good coverage estimator for species diversity suggested a significant coverage, with values ranging between 92 and 97% for Good coverage. Conserved taxa corresponded to aprox. 52% of all sequences. This study suggests that human-contaminated environments may influence bacterioplankton diversity.

The La Plata River, located at 35°S on the Atlantic coast, is one of the largest waterways of South America. It carries a large amount of suspended particulate and dissolved organic matter, and is considered among the most turbid waters of the world. Very high values of total ...

Oithonid species are key components of estuarine zooplankton communities. The spatial distribution of Oithona nana and O. helgolandica (syn. O. similis) and their population dynamics were studied for the first time in a shallow temperate estuarine system in the South West Atlantic Ocean. Here we estimated the influence of physical (salinity and temperature) and trophic (chlorophyll a and bacterioplankton concentrations) factors on O. nana and O. helgolandica life history traits. O. nana abundance and biomass were higher at the surface salinity front but were not correlated with higher egg production rates, which suggests the presence of some retention mechanism that favors population aggregation. In a spatial context, the high reproductive activity near the La Plata River runoff in comparison with the coastal system nearby, suggests that this system might favor the proliferation of O. nana populations. However, smaller females with relatively few and smaller eggs per sac occurred un...

Abstract The Rio de la Plata drains the second largest basin in South America and the fifth-largest in the world. In this study, we analyzed the influence of the estuarine plume generated by the river (Plata plume) upon the abundance, composition, and size structure of the copepod's community during summer. Zooplankton samples were collected by employing 67 and 300 μm mesh size nets, water samples were obtained to quantify bacterioplankton, protozooplankton and phytoplankton biomass, and CTD profiles were also obtained during a summer cruise. Amongst the 60 copepods categories identified, calanoid and cyclopoid nauplii were numerically dominant across the shelf, followed by small-sized copepodites of Para-Clausocalanidae and Oithonidae. The presence of adults of the small and medium-sized Centropages calaninus, Calocalanus plumulosus, Delibus sewelli, Temora turbinata and Oithona flemingeri represented a novel finding for the area, attributed mainly to the small mesh size used. Copepods community was organized into four assemblages that occupied distinct areas closely related to different water masses (Plata Plume Waters, Subantarctic Shelf Waters, and Tropical Waters). Each assemblage was characterized by species abundance, composition, and the indicator species, being salinity and temperature the main explanatory variables for these assemblage's arrangement. The Plata plume was characterized by higher numerical abundances, especially of the small-sized fraction, which was also the most diverse, denoting the strong ecological impact of the plume in summer. Offshore the plume, copepods size composition was homogeneous, with the addition of medium and large-sized taxa, which were important discriminating species between assemblages. Our results allow to infer that in the plume the energy would be channeled through a microbial food web in summer, which could be a less productive season as occur for the rest of the shelf. Given the large spatial scale of the Plata plume (ca.1000 km), our results could reflect impacts on the plankton community and trophic web at a regional scale. Taking into account that models predict an increase of precipitations in southern South America, and consequently, on river discharges, our results could aid in understanding aspects of the impact of global change in a region relevant to fisheries of Argentina and Uruguay.