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Vogler R.,University of the Republic of Uruguay | Arreguin-Sanchez F.,National Polytechnic Institute of Mexico | Lercari D.,University of the Republic of Uruguay | del Monte-Luna P.,National Polytechnic Institute of Mexico | And 2 more authors.
Ecological Modelling

The trophodynamics of the Río de la Plata ecosystem over a long time scale (from 1948 to 2008) were simulated using a food-web model forced by two environmental factors. The Atlantic Meridional Mode (meridional sea surface temperature anomalies) was used as regional forcing, and the Río de la Plata (RdlP) runoff was applied as local forcing. The entire food web was impacted by the regional forcing on a decadal scale; at the inter-annual scale, this remote factor had partial effects on the base of the food web. The RdlP runoff impacted primary producers and secondary consumers at the inter-annual scale. The higher effects of the local forcing were temporally coupled with seven of the strongest El Niño events from 1950 to 2008 (1957-1958, 1965-1966, 1972-1973, 1982-1983, 1986-1987, 1991-1992, 1997-1998). In contrast, the lower effects of RdlP runoff on the food web were coupled with six of the strongest La Niña events since 1950 (1950-1951, 1954-1956, 1964, 1970-1971, 1974-1975, 1988-1989). Total system biomass (trophic web attribute) and a measure of system entropy (holistic indicator) were used to identify ecosystem degradation. The entropy and total biomass of the RdlP ecosystem showed two opposite phases: before and after the early 1970s. During the period 1948-1971, the system showed high entropy and low total biomass, indicating high degradation. This cycle was reversed after 1972, and prevailed until the beginning of the 2000s. During this new cycle, the system entropy decreased and it was compensated by an increase in total system biomass. A sustainable entropy gain occurred after 2003, suggesting a new period of ecosystem degradation. The findings are discussed in light of temporal changes in the structural properties of this coastal ecosystem. © 2015 Elsevier B.V. Source

Fonseca G.,Federal University of Sao Paulo | Fonseca G.,University of Sao Paulo | Maria T.F.,Rio de Janeiro State Federal University | Kandratavicius N.,Laboratorio Of Oceanografia Y Ecologia Marina | And 4 more authors.
Marine Biodiversity

The majority of studies have advocated that diversity of marine nematodes increases with increasing sediment grain size, although the opposite trend has also been suggested. The controversy is partially caused by not taking into account the effect of density on patterns of diversity and by analyzing datasets from different environments. The present study investigated nematode assemblages from sediments varying from very fine sand (mean grain size of 0.12 mm) to very coarse sand (1 mm) in shallow sublittoral marine environments. Contrary to previous studies, species richness was constant along the granulometric spectrum, despite significant changes in composition. The dominant genera were separated into five groups according to their optimum distribution and there was little overlap between these groups. Concepts from the niche theory explain to some extent the observed patterns. For instance, some of the coexisting genera were from different feeding types. © 2014, Senckenberg Gesellschaft für Naturforschung and Springer-Verlag Berlin Heidelberg. Source

Machado I.,University of the Republic of Uruguay | Barreiro M.,Institute Fisica | Calliari D.,Ecologia Funcional de Sistemas Acuaticos | Calliari D.,Laboratorio Of Oceanografia Y Ecologia Marina
Continental Shelf Research

Seasonal and interannual satellite chlorophyll-a variability (CSAT) was assessed in the Southwestern Atlantic based on over 11 years (1997-2008) of Sea-Viewing Wide Field-of-View Sensor data. An Empirical Orthogonal Function analysis of the seasonal CSAT cycle showed strong variability and the spatial structure of the leading pattern revealed an opposite behavior over the continental shelf north and south of 37°S with low (high) biomass south (north) of 37°S during wintertime. This distribution is related to the lack of stratification of the water column in the southernmost region during winter due to heat loss to the atmosphere as well as wind induced and convective mixing, in contrast to a vertically stable water column north of 37°S induced by the fresh Río de la Plata discharge. High variability in CSAT between 47 and 51°S in the inner and outer shelves could be related to the southern Patagonian fronts. On interannual time scales the influence of El Niño-Southern Oscillation on CSAT during spring was estimated and related to wind stress, vertical velocities and Río de la Plata discharge. During El Niño events the continental shelf north of 45°S is characterized by high CSAT values (anomalies>0.5mgm-3) while low values are found to the south (anomalies<-0.5mgm-3), except for positive anomalies near to the Malvinas Islands. The opposite pattern occurred in La Niña years. Conversely, the Brazil-Malvinas confluence has a lower CSAT in El Niño years in comparison with La Niña years. The higher chlorophyll-a of some areas over the shelf north of 45°S during El Niño was supported by increased Río de la Plata discharges, northerly winds anomalies and upwelling generated in the shelf between 33 and 39°S. The winds tend to retain the patch of high chlorophyll-a off Río de la Plata in spring, but advect it toward the Brazilian coast in summer. This result indicates the extreme importance of wind variability for the spreading or retention of phytoplankton in this area. No support was found for a mechanism linking Ekman pumping and CSAT variability over the continental shelf south of 45°S and in the Malvinas-Brazil confluence. © 2013. Source

MacHado I.,University of the Republic of Uruguay | Vera M.,Laboratorio Of Oceanografia Y Ecologia Marina | Calliari D.,Ecologia Funcional de Sistemas Acuaticos | Calliari D.,Laboratorio Of Oceanografia Y Ecologia Marina | Rodriguez-Grana L.,University of the Republic of Uruguay
Marine Biodiversity Records

This is the first record of a ladyfish (Elops smithi) larva in Uruguay and the southernmost South Atlantic record. We provide morphological-merisitc and environmental information about the larva collected in March 2010 in brackish waters of the Solís Grande estuary. The sampling site was 0.9 m depth, water was warm (21.7 °C), low salinity (12.3) and with high oxygen content (7.7 mg l-1). The larva was very transparent, 31 mm in standard length and had a total of 76 myomeres. The dorsal fin (24 rays) and the anal fin (16 rays) did not overlap. The caudal fin was forked; the pectoral fin without rays and pelvic fin was in an early phase. The swim bladder was inverted U shaped. The half premaxilla had 8 teeth and the half mandible 10 (of similar size and appearance). Pigments were present in the ventral line (from the thorax to anus) and in the middle lateral trunk and caudal peduncle line. These characteristics suggested an early-metamorphic stage of the larva. This species is recorded with low abundances in southern Brazil. The collection of this individual occurred during a period of strong El Niño (2009-2010). These events are associated with warm sea surface temperature anomalies in the south-western Atlantic and northerly winds anomalies in the Brazilian-Uruguayan continental shelf. © 2012 Marine Biological Association of the United Kingdom. Source

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