Zooplankton can amplify changes resulting from physical forcing associated with climate change at interannual and longer time scales, so multi-year time series data for the pelagic assemblage can provide useful information about climate-ecosystem interactions. Zooplankton biomass and taxonomic composition were analyzed for the region over the southern Patagonian shelf (SPS) for March 1994 to 2012 to describe interannual patterns of variation, determine the spatial consistency and dominant scale of temporal variability, and examine their relation to the regional hydrography. The biomass of selected taxa, including primarily copepods, amphipods, and euphausiids, decreased in 2003 and remained low until 2012. These patterns were associated with a moderate increase in sea surface temperature. Our observations could not establish the causal mechanisms, but the observed biomass decrease might be related to variation in northward current flow over the SPS, which is driven by large-scale climatological forcing and would result in reduced cold-water availability over SPS. Understanding the drivers of interannual variability in zooplankton composition and biomass of this ecosystem is essential for prediction of impacts of climate change on the pelagic ecosystem, including important commercially fished species.

ABSTRACT Although Serratosagitta tasmanica is widely distributed, there is little information on how hydrology affects its distribution, abundance and demography. In this study we analyzed the distribution, carbon content and population structure of S. tasmanica in the Southwestern Atlantic Ocean. Samples were collected at 34°–39°S (Northern Argentine Continental Shelf in winters of 1999 and 2000) and at 47°–55°S (Southern Argentine Continental Shelf in spring 2005, summer 2006 and winter 2006). The analysis of more than 8500 individuals showed that its dominance decreased spatially from south to north, whereas biomass (mgC/m2) increased temporally by three orders of magnitude between spring (4.06) and summer (12.7). In the southern area the presence of all maturity stages in all seasons suggests year-round reproduction, with maximum reproductive activity in winter. Body length increased with increasing latitude and decreased with temperature. We detected differences in the morphology of seminal vesicles and ovary length between mature specimens. In the northern area all individuals exhibited short-type ovaries whereas in the southern area individuals had either short or long ovaries, suggesting that some individuals of the latter area had been advected from the Southern Pacific Ocean through the water discharged from the Magellan Strait.

Se analizaron las variables temperatura y salinidad en verano, durante el período 1996-2001 en el área de cría del efectivo patagónico de la merluza argentina Merluccius hubbsi. Estas variables oceanógraficas se relacionaron con las variaciones en la abundancia de la población, a través de un modelo lineal general. Se determinaron los valores medios y las anomalías de temperatura y salinidad de fondo. Las anomalías térmicas positivas más extremas se produjeron en 1999 y 2000, mientras que el año más frío fue 1996. La anomalía de salinidad más baja se registró en 1996 y la más alta en el 2000. La merluza se concentró principalmente en las zonas de gradientes térmicos y salinos Los juveniles se hallaron preferentemente en el Golfo San Jorge en aguas con temperaturas entre 8º y 10°C y salinidades entre 33,2 y 33,6 y los adultos dentro y fuera del mismo, con temperaturas de fondo entre 8º y 12°C y salinidades 33,2 y 33,5. Las mayores densidades de juveniles se hallaron en aguas de menor profundidad, con valores elevados de salinidad y menores valores de temperatura respecto de los adultos. Estos se concentraron tanto en el sector norte del golfo y en la Bahía Camarones, en aguas con relativamente alta temperatura y escasa profundidad, como sobre la plataforma frente al golfo, donde las aguas tienen menor salinidad debido a la deriva de la Corriente Patagónica de aguas diluidas. No se observaron cambios en la distribución de la población en los años con anomalías ambientales marcadas.Summer temperature and salinity data in the nursery ground of the Patagonian stock of Argentine hake Merluccius hubbsi recorded from 1996 to 2001 were analyzed. These oceanographic variables were related to variations in the hake population abundance by means of a general linear model. Mean values and anomalies of bottom temperatures and salinity fields were determined. The most extreme positive thermal anomalies occurred in 1999 and 2000, whereas 1996 was the coldest year. The salinity anomaly was lowest in 1996 and highest in 2000. Argentine hake was found mainly in thermal and saline gradient zones. Juveniles were found mainly within the San Jorge Gulf with temperatures ranging from 8º to 10°C and salinities of 33.2 to 33.6, whereas adults were located inside and outside the gulf, where bottom water temperatures oscillated between 8º and 12°C and salinities ranged from 33.2 to 33.5. Juvenile densities were highest in shallower waters with higher salinities and lower temperatures than those inhabited by the adults. Adult hake were concentrated in the northern part of the Gulf and Camarones Bay, in shallow, relatively warm waters, as well as over the shelf waters off the gulf, where the salinity is low due to the drift of diluted waters from the Patagonian Current. The population distribution did not change in years with striking environmental anomalies.

Summer temperature and salinity data in the nursery ground of the Patagonian stock of Argentine hake Merluccius hubbsi recorded from 1996 to 2001 were analyzed. These oceanographic variables were related to variations in the hake population abundance by means of a general linear model. Mean values and anomalies of bottom temperatures and salinity fields were determined. The most extreme positive thermal anomalies occurred in 1999 and 2000, whereas 1996 was the coldest year. The salinity anomaly was lowest in 1996 and highest in 2000. Argentine hake was found mainly in thermal and saline gradient zones. Juveniles were found mainly within the San Jorge Gulf with temperatures ranging from 8o to 10oC and salinities of 33.2 to 33.6, whereas adults were located inside and outside the gulf, where bottom water temperatures oscillated between 8o and 12oC and salinities ranged from 33.2 to 33.5. Juvenile densities were highest in shallower waters with higher salinities and lower temperatures than those inhabited by the adults. Adult hake were concentrated in the northern part of the Gulf and Camarones Bay, in shallow, relatively warm waters, as well as over the shelf waters off the gulf, where the salinity is low due to the drift of diluted waters from the Patagonian Current. The population distribution did not change in years with striking environmental

Summer temperature and salinity data in the nursery ground of the Patagonian stock of Argentine hake Merluccius hubbsi recorded from 1996 to 2001 were analyzed. These oceanographic variables were related to variations in the hake population abundance by means of a general linear model. Mean values and anomalies of bottom temperatures and salinity fields were determined. The most extreme positive thermal anomalies occurred in 1999 and 2000, whereas 1996 was the coldest year. The salinity anomaly was lowest in 1996 and highest in 2000. Argentine hake was found mainly in thermal and saline gradient zones. Juveniles were found mainly within the San Jorge Gulf with temperatures ranging from 8º to 10ºC and salinities of 33.2 to 33.6, whereas adults were located inside and outside the gulf, where bottom water temperatures oscillated between 8º and 12ºC and salinities ranged from 33.2 to 33.5. Juvenile densities were highest in shallower waters with higher salinities and lower temperatures than those inhabited by the adults. Adult hake were concentrated in the northern part of the Gulf and Camarones Bay, in shallow, relatively warm waters, as well as over the shelf waters off the gulf, where the salinity is low due to the drift of diluted waters from the Patagonian Current. The population distribution did not change in years with striking environmental anomalies.

Salinity and temperature data recorded during 1996-2003 within the distribution area of the Patagonian stock of Argentine hake Merluccius hubbsi were analysed. These oceanographic variables were then related to fluctuations in the abundance of the species by means of a generalized linear model. Mean bottom temperature and salinity fields were graphed and anomalies for this period were estimated. During 1998 and 2002 the highest and lowest mean temperatures were recorded, respectively, showing the most remarkable anomalies. Highest mean salinity was recorded during 1999 and in terms of anomalies during 2003 lowest salinities were recorded for the whole area. Highest juvenile concentrations were found in waters with bottom temperatures between 7ºC and 10ºC and salinities between 33.3 and 33.8 distributed to the north and within the San Jorge Gulf and in midshelf between the 50 m and 100 m isobaths, to the southern zone of the Valdés Peninsula. Adult concentration was higher at the centre of the shelf, decreasing towards the coastal sector, at approximately 6ºC and 9ºC and between 33.4 and 33.9. Regression coefficients evidenced highest juvenile abundances in shallow areas with low salinity, and highest adult abundances in regions with low temperature and high salinity. No spatial shifts in the distribution of the species were observed during marked temperature or salinity anomalies.

Salinity and temperature data recorded during 1996-2003 within the distribution area of the Patagonian stock of Argentine hake Merluccius hubbsi were analysed. These oceanographic variables were then related to fluctuations in the abundance of the species by means of a generalized linear model. Mean bottom temperature and salinity fields were graphed and anomalies for this period were estimated. During 1998 and 2002 the highest and lowest mean temperatures were recorded, respectively, showing the most remarkable anomalies. Highest mean salinity was recorded during 1999 and in terms of anomalies during 2003 lowest salinities were recorded for the whole area. Highest juvenile concentrations were found in waters with bottom temperatures between 7 degrees C and 10 degrees C and salinities between 33.3 and 33.8 distributed to the north and within the San Jorge Gulf and in midshelf between the 50 m and 100 m isobaths, to the southern zone of the Valdes Peninsula. Adult concentration was higher at the centre of the shelf, decreasing towards the coastal sector, at approximately 6 degrees C and 9 degrees C and between 33.4 and 33.9. Regression coefficients evidenced highest juvenile abundances in shallow areas with low salinity, and highest adult abundances in regions with low temperature and high salinity. No spatial shifts in the distribution of the species were observed during marked temperature or salinity anomalies.

Se analizaron las variables de temperatura y salinidad en el invierno durante el periodo 1996-2003 en el area de distribucion del efectivo patagonico de la merluza argentina Merluccius hubbsi; estas variables oceanograficas se relacionaron con las variaciones en la abundancia de la especie, a traves de un modelo lineal general. Se determinaron los campos medios de fondo y las anomalias de temperatura y salinidad para ese periodo. El ano 1998 presento la temperatura promedio mas alta y el 2002 la mas baja, indicando las anomalias mas destacadas. La salinidad promedio mas alta se registro en 1999 y en terminos de anomalias, el 2003 fue, en toda el area, de menor salinidad. Las mayores concentraciones de juveniles se observaron en aguas con temperaturas de fondo entre 7°C y 10°C y salinidades entre 33,3 y 33,8 distribuidas en el interior y norte del Golfo San Jorge y en la plataforma media, entre la isobata de 50 y 100 m, hasta la zona sur de la Peninsula Valdes. La distribucion de adultos se concentro en el centro de la plataforma, disminuyendo hacia el sector costero, aproximadamente entre 6o y 9oC y entre 33,4 y 33,9 de salinidad. Los coeficientes de regresion indicaron que las mayores abundancias de juveniles se hallaron en areas con menor salinidad y menor profundidad, mientras que las mayores abundancias de los adultos se encontraron en regiones de menor temperatura y mayor salinidad respecto de los juveniles. No se observaron corrimientos espaciales en la distribucion de la especie cuando las anomalias de temperatura o salinidad fueron muy marcadas

The physical aspects of the Subtropical Shelf Front (STSF) for the Southwest Atlantic Continental Shelf were previously described. However, only scarce data on the biology of the front is available in the literature. The main goal of this paper is to describe the physical, chemical and biological properties of the STSF found in winter 2003 and summer 2004. A cross-section was established at the historically determined location of the STSF. Nine stations were sampled in winter and seven in summer. Each section included a series of conductivity-temperature-depth (CTD) stations where water samples from selected depths were filtered for nutrient determination. Surface samples were taken for chlorophyll a (Chl-a) determination and plankton net tows carried out above and below the pycnocline. Results revealed that winter was marked by an inner-shelf salinity front and that the STSF was located on the mid-shelf. The low salinity waters in the inner-shelf indicated a strong influence of freshwater, with high silicate (72μM), suspended matter (45mgl−1), phosphate (2.70μM) and low nitrate (1.0μM) levels. Total dissolved nitrogen was relatively high (22.98μM), probably due to the elevated levels of organic compound contribution close to the continental margin. Surface Chl-a concentration decreased from coastal well-mixed waters, where values up to 8.0mgm−3 were registered, to offshore waters. Towards the open ocean, high subsurface nutrients values were observed, probably associated to South Atlantic Central Waters (SACW). Zooplankton and ichthyoplankton abundance followed the same trend; three different groups associated to the inner-, mid- and outer-shelf region were identified. During summer, diluted waters extended over the shelf to join the STSF in the upper layer; the concentration of inorganic nutrients decreased in shallow waters; however, high values were observed between 40 and 60m and in deep offshore waters. Surface Chl-a ranged 0.07–1.5mgm−3; winter levels were higher. Three groups of zoo and ichthyoplankton, separated by the STSF, were also identified. Results of the study performed suggest that the influence of freshwater was stronger during winter and that abundance distribution of Chl-a, copepods and ichthyoplankton was related to the Plata Plume Waters (PPW), rather than to the presence of the STSF. During summer, when the presence of freshwater decreases, plankton interactions seem to take place in the STSF.

This paper provides an overview of the research being carried out at the moment by a group of Argentinean scientists working on the subjects of marine biodiversity and oceanography.When the idea of the Census of Marine Life (CoML) was proposed following the Symposium held during the IAPSO-IABO conference in Mar del Plata in October 2001, there was a wide response from the marine scientific community.Information about current research projects, as well as plans for future work in the context of the CoML, were then obtained from about 70 scientists (Appendix I) belonging to 12 institutions located along the Argentinean coast (Appendix II, Figure 1).This has been used to illustrate what is currently being pursued in marine biodiversity in Argentina and which subjects are considered as priority for future research in the area.This paper is, thus, not an historical update of the knowledge of marine biodiversity, but it attempts to give an idea of the current situation and what is planned for the future.The development of an extensive database of what is known on marine biodiversity in the region is considered to be a necessity, but it constitutes a complete project on its own; as such it is included in the proposals for future work (see Future Work in this paper).It is emphasised that this synthesis is not exhaustive in the content of the topics being studied or in the number of researchers working in marine biodiversity in the country.It is, though, considered to be a representative sample of the knowledge in marine science in Argentina today.This is a starting point for the CoML project in South America and it is hoped that, as it develops, it will be improved by the active participation, advice and experience of many other scientists in the region.

This paper provides an overview of the research being carried out at the moment by a group of Argentinean scientists working on the subjects of marine biodiversity and oceanography. When the idea of the Census of Marine Life (CoML) was proposed following the Symposium held during the IAPSO-IABO conference in Mar del Plata in October 2001, there was a wide response from the marine scientific community. Information about current research projects, as well as plans for future work in the context of the CoML, were then obtained from about 70 scientists (Appendix I) belonging to 12 institutions located along the Argentinean coast (Appendix II, Figure 1). This has been used to illustrate what is currently being pursued in marine biodiversity in Argentina and which subjects are considered as priority for future research in the area. This paper is, thus, not an historical update of the knowledge of marine biodiversity, but it attempts to give an idea of the current situation and what is planned for the future. The development of an extensive database of what is known on marine biodiversity in the region is considered to be a necessity, but it constitutes a complete project on its own; as such it is included in the proposals for future work (see Future Work in this paper). It is emphasised that this synthesis is not exhaustive in the content of the topics being studied or in the number of researchers working in marine biodiversity in the country. It is, though, considered to be a representative sample of the knowledge in marine science in Argentina today. This is a starting point for the CoML project in South America and it is hoped that, as it develops, it will be improved by the active participation, advice and experience of many other scientists in the region.