Leonardo Ortega

Multiannual and Seasonal Variability of Water Masses and Fronts Over the Uruguayan Shelf

Abstract Seasonal (autumn and spring) and multiannual (1991, 1995, 1996, 1997, 1998, and 2001) variability in the composition of water masses on the Uruguayan shelf were analyzed. The main difference between seasons was the presence of Tropical Water (TW) and a relative dominance of Subtropical Water (STW) over Subantartic Water (SAW) in autumn, whereas spring was characterized by a dominance of SAW and the absence of TW. Changes in the composition of water masses, surface temperature distributions, and front positions and strengths are discussed in regards to biological implications. Our results reveal seasonal changes in the frontal zone position and suggest an enhaced migration during El Niño Southern Oscillation (ENSO) warm and cold episodes, reaching higher latitudes during the former (e.g., autumn of 1998). During cold episodes, the position of the frontal zone reached lower latitudes, with prevailing cold waters over the shelf. Higher frontal strength was observed during ENSO episodes, mainly because of the haline component of CW at the surface. The combination of highly variable freshwater inputs and the occurrence of shelf convergences produced a distinctive hydrographic system with a high degree of seasonal and interannual variation and an evident impact on ecological processes.

Impacts of Climate Variability on Latin American Small-scale Fisheries

Small-scale fisheries (SSFs) are social-ecological systems that play a critical role in terms of food security and poverty alleviation in Latin America. These fisheries are increasingly threatened by anthropogenic and climatic drivers acting at multiple scales. We review the effects of climate variability on Latin American SSFs, and discuss the combined effects of two additional human drivers: globalization of markets and governance. We show drastic long-term and large-scale effects of climate variability, e.g., sea surface temperature anomalies, wind intensity, sea level, and climatic indices, on SSFs. These variables, acting in concert with economic drivers, have exacerbated stock depletion rates in Latin American SSFs. The impact of these drivers varied according to the life cycle and latitudinal distribution of the target species, the characteristics of the oceanographic systems, and the inherent features of the social systems. Our review highlights the urgent need to improve management and governance systems to promote resilience as a way to cope with the increasing uncertainty about the impacts of climate and globalization of markets on Latin American SSFs.

Distribution of Large Benthic Gastropods in the Uruguayan Continental Shelf and Río de la Plata Estuary

Abstract We analyzed the distribution and ecology of large gastropods inhabiting the continental shelf of Uruguay and the Río de la Plata estuary, in depths ranging from 4 to 62 m. Seven species belonging to Tonnidae, Ranellidae, Muricidae, Nassariidae, and Volutidae were collected. While the seven species recorded in this study have been previously reported for the Uruguayan coast, here we provide the first detailed description of its habitat preferences in terms of depth, salinity, and sea bottom temperatures. Clustering analysis of stations based on biological data (presence/ absence of species) indicated a spatial segregation of the large gastropods assemblages in three areas: estuarine, low specific richness, dominated by Rapana venosa; inshore (10 to 36 m), high richness, codominated by Zidona dufresnei and Pachycymbiola brasiliana; and offshore (21 to 62 m), intermediate richness, characterized by Z. dufresnei. Mean values for environmental parameters showed significant differences among clusters of stations. Direct developers were more ubiquitous than planktotrophic developers. On the other hand, the exotic planktotrophic species R. venosa dominated the estuarine area. This pattern is not coincident with predictions based on life history traits, such as dispersal capabilities; this suggests that generalizations in this respect are complicated and scale and species dependent.

Effects of Climate Variability on the Morphodynamics of Uruguayan Sandy Beaches

ABSTRACT Oretga, L.; Celentano, E.; Finkl, C., and Defeo, O., 2013. Effects of climate variability on the morphodynamics of Uruguayan sandy beaches. Effects of long-term trends in climatic variability on the morphodynamics of a reflective and a dissipative sandy beach in Uruguay (SW Atlantic Ocean) were analyzed. The Atlantic Multidecadal Oscillation (AMO) alternates between warm and cold cycles with a periodicity of roughly 70 years, with a shift toward a warm phase since 1995, resulting in an increase of sea surface temperature in the study area. Wind speed anomalies (WSA) also increased through time and were associated with an increasing speed of southerly winds, particularly after 1997. Beach morphodynamics showed no statistically significant trends in grain size, but long-term morphodynamic patterns differed between beaches: the dissipative beach showed an increase in swash and beach width, Deans parameter, and the Beach Index (a measure of beach morphodynamic state). At the same time, the slope decreased, augmenting the beachs dissipative characteristics. The reflective beach showed an increase in slope and swash width through time, and a decrease in the Beach Index, indicating an intensification of reflective characteristics. Long-term morphodynamic changes were more evident in the dissipative beach and related to climate forcing (e.g. WSA). A higher resilience was observed in the reflective beach, even though an increasing frequency of storms is affecting both beaches. Accelerating erosion, rising sea levels, and expanding urban development in the Uruguayan coast could affect biodiversity and critical habitats. Multidisciplinary investigation programs and conservation strategies are needed to mitigate negative anthropogenic effects on these ecosystems.

Stellifer rastrifer (Pisces: Sciaenidae): first Uruguayan records and a 1200 km range extension

Stellifer rastrifer, a coastal fish species that inhabits the tropical and south-western Atlantic Ocean is reported for the first time from the Uruguayan coast. Its geographic distribution range is extended southward more than 1200 km. Population descriptors such as a length frequency distribution (LFD) and a length-weight relationship are presented. Some warm circulation events are suggested as a putative factor explaining the occurrence of the fish in the area.

Delimitation of domains in the external Río de la Plata estuary, involving phytoplanktonic and hydrographic variables

Neste trabalho foram analisadas no Rio da Prata as variaveis hidrologicas (temperatura e salinidade) e biologicas (clorofila, feopigmentos e especies de fitoplâncton) por ocasiao do outono e primavera (Uruguai). A biomassa do fitoplâncton, expressa como teor de clorofila, alcancou um maximo de 6,1 µg L-1 no outono e 22,8 µg L-1 na primavera. Esses maximos foram encontrados na zona frontal e na area marinha adjacente. Por meio de analises multivariadas, foram identificados quatro dominios: Ribeirinho, Estuarino, Frontal e Oceânico, com base na salinidade e profundidade no outono e na salinidade e clorofila na primavera. Em ambas as estacoes, os dominios Ribeirinho e Estuarino (bordas leste e oeste) estiveram localizados no mesmo local, mas, na primavera, um dominio adicional foi encontrado no Canal Oriental (dominio Canal). Tanto a salinidade quanto a concentracao de clorofila aumentou do dominio Ribeirinho para o Frontal, o que se correlacionou de forma positiva com salinidades ≤ 14, o que sugere que a concentracao de clorofila esta sendo modulada principalmente pela influencia oceânica no sentido de melhorar a disponibilidade de luz. Enquanto a salinidade tende a aumentar no sentido do dominio Oceânico, a biomassa de fitoplâncton diminui. Aparentemente, nessa regiao a concentracao de clorofila estaria sendo regulada pela combinacao de disponibilidade de luz e forrageio. Entretanto, novas pesquisas necessitam ser desenvolvidas para dar sustentacao a essas hipoteses.

The Effect of Climate Variability on the Abundance of the Sandy Beach Clam (Mesodesma mactroides) in the Southwestern Atlantic

ABSTRACT Manta, G.; Barreiro, M.; Ortega, L., and Defeo, O., 2017. The effect of climate variability on the abundance of the sandy beach clam (Mesodesma mactroides) in the southwestern Atlantic. The yellow clam Mesodesma mactroides is a fast-growing, short-lived species that inhabits sandy beaches of the southwestern Atlantic Ocean (SAO). The purpose of this study was to relate interannual fluctuations of the yellow clam population in Uruguay to climate circulation anomalies in the SAO. Twenty-three years of clam abundance, as well as sea-surface temperature anomalies (SSTA), salinity, and wind stress anomalies (WSA) from oceanic reanalyses were used. Composites and linear regressions showed that the best scenario for high abundance of M. mactroides is characterized by cold and salty waters and onshore WSA on the Uruguayan Atlantic coast. These local WSA are part of a cyclonic configuration of WSA in the SAO that forces negative SSTA in the region. High and low M. mactroides abundance tended to occur along with La Niña and El Niño events in the equatorial Pacific Ocean, respectively. These results suggest that interannual fluctuations in M. mactroides abundance are not only locally but also remotely controlled by regional- and global-scale climate variability modes.

Tamoya haplonema (Cnidaria: Cubozoa) from Uruguayan and adjacent waters: oceanographic context of new and historical findings

New records of the cubozoan jellyfish Tamoya haplonema in Uruguayan waters are reported together with historical records for the region, and associated with the oceanographic conditions at the moment of the finding. Occurrences of the species are mainly associated with positive Sea Surface Temperature Anomalies especially during summer months when the intrusion of warm oceanic waters to the Uruguayan coastline is stronger. This was particularly strong during 2012–2013, when a dry period enhanced this scenario. This species is the only cubozoan present in Uruguay, with a sporadic occurrence and so far has no appreciated negative effects on public health. However, from observed increasing frequency of positive temperature anomalies it would be reasonable to predict a future southward shift in the latitudinal distribution of T. haplonema. In this context, occurrence of this toxic species along Uruguayan coastal waters must be considered with particular attention to the potential negative impact on tourism and on general public health.

Intensificación de floraciones de dinoflagelados marinos en Uruguay

Las perdidas economicas y problemas de salud ocasionados por las Floraciones Algales Nocivas (FAN) hacen fundamental su comprension. Mientras continua el debate sobre si el aumento de los reportes se debe a mayor actividad de monitoreo o a un incremento real en su ocurrencia, los problemas causados por las FAN estan creciendo mundialmente. Se espera que las FAN aumenten a causa del cambio climatico por un incremento en la temperatura superficial del mar, mayor estratificacion, acidificacion del oceano y eutrofizacion, principalmente en las zonas costeras. Uruguay no escapa a esa tendencia y en los ultimos anos ha mostrado un incremento en la intensidad de algunas floraciones (mayor densidad y duracion), aunque sin cambios en su frecuencia. Especies que comunmente producian floraciones en la actualidad lo hacen con mayor abundancia (106 cel /l) y duracion (entre 3 y 5 semanas). Lo mismo ocurre con algunas especies toxicas (i.e. Dinophysis cf. acuminata) para las cuales la duracion de las vedas en moluscos ha mostrado un incremento, con un maximo de 189 dias durante 2015. El aumento de estas floraciones, tanto en el espacio como en el tiempo, podria estar asociado a un aumento de la temperatura y la concentracion de nutrientes.