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Lutz V.A.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | Lutz V.A.,CONICET | Segura V.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | Dogliotti A.I.,CONICET | And 4 more authors.
Journal of Plankton Research | Year: 2010

In satellite images of the world ocean the Argentine Sea is one of the areas of highest chlorophyll-a (Chl a) concentration. Here we analyze the spatial variability in primary production in relationship to phytoplankton biomass, and some relevant optical and physical characteristics observed during spring 2005. High Chl a concentrations were found in frontal areas, mainly at the shelf-break (19.0 mg m-3) and Grande Bay (28.6 mg m -3), with the lowest values offshore (0.4 mg m-3). Integrated production also varied widely from ∼275 to 5480 mg C m -2 d-1. Variations in the Chl a/in vivo-fluorescence, and photosynthetic parameters were related to the absorption characteristics of phytoplankton, indicating the influence of variations in the phytoplankton community composition. Surface Chl a explained only 51 of the variance in integrated primary production. Neither integrated production, nor the photosynthetic parameters were significantly related to seawater temperature. The simple satellite model used here resulted in significant underestimation of field primary production values (Absolute Percentage Difference > 50). Our results indicate that a more adequate satellite model of production, making use of local photosynthetic parameters and vertical distribution of biomass, should be developed for this region.

Pitt K.A.,Griffith University | Duarte C.M.,University of Western Australia | Duarte C.M.,University of the Balearic Islands | Duarte C.M.,King Abdulaziz University | And 7 more authors.
PLoS ONE | Year: 2013

Jellyfish form spectacular blooms throughout the world's oceans. Jellyfish body plans are characterised by high water and low carbon contents which enables them to grow much larger than non-gelatinous animals of equivalent carbon content and to deviate from non-gelatinous pelagic animals when incorporated into allometric relationships. Jellyfish have, however, been argued to conform to allometric relationships when carbon content is used as the metric for comparison. Here we test the hypothesis that differences in allometric relationships for several key functional parameters remain for jellyfish even after their body sizes are scaled to their carbon content. Data on carbon and nitrogen contents, rates of respiration, excretion, growth, longevity and swimming velocity of jellyfish and other pelagic animals were assembled. Allometric relationships between each variable and the equivalent spherical diameters of jellyfish and other pelagic animals were compared before and after sizes of jellyfish were standardised for their carbon content. Before standardisation, the slopes of the allometric relationships for respiration, excretion and growth were the same for jellyfish and other pelagic taxa but the intercepts differed. After standardisation, slopes and intercepts for respiration were similar but excretion rates of jellyfish were 10× slower, and growth rates 2× faster than those of other pelagic animals. Longevity of jellyfish was independent of size. The slope of the allometric relationship of swimming velocity of jellyfish differed from that of other pelagic animals but because they are larger jellyfish operate at Reynolds numbers approximately 10× greater than those of other pelagic animals of comparable carbon content. We conclude that low carbon and high water contents alone do not explain the differences in the intercepts or slopes of the allometric relationships of jellyfish and other pelagic animals and that the evolutionary longevity of jellyfish and their propensity to form blooms is facilitated by their unique body plans. © 2013 Pitt et al.

Piola A.R.,Servicio de Hidrografia Naval | Piola A.R.,University of Buenos Aires | Martinez Avellaneda N.,University of Hamburg | Guerrero R.A.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | And 5 more authors.
Ocean Science | Year: 2010

The Patagonia continental shelf located off southeastern South America is bounded offshore by the Malvinas Current, which extends northward from northern Drake Passage (∼55deg; S) to nearly 38deg; S. The transition between relatively warm-fresh shelf waters and Subantarctic Waters from the western boundary current is characterized by a thermohaline front extending nearly 2500 km. We use satellite derived sea surface temperature, and chlorophyll-a data combined with hydrographic and surface drifter data to document the intrusions of slope waters onto the continental shelf near 41deg; S. These intrusions create vertically coherent localized negative temperature and positive salinity anomalies extending onshore about 150 km from the shelf break. The region is associated with a center of action of the first mode of non-seasonal sea surface temperature variability and also relatively high chlorophyll-a variability, suggesting that the intrusions are important in promoting the local development of phytoplankton. The generation of slope water penetrations at this location may be triggered by the inshore excursion of the 100 m isobath, which appears to steer the Malvinas Current waters over the outer shelf.

Matano R.P.,Oregon State University | Combes V.,Oregon State University | Piola A.R.,CONICET | Guerrero R.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | And 6 more authors.
Journal of Geophysical Research C: Oceans | Year: 2014

A high-resolution model is used to characterize the dominant patterns of sea surface salinity (SSS) variability generated by the freshwater discharges of the Rio de la Plata (RdlP) and the Patos/Mirim Lagoon in the southwestern Atlantic region. We identify three dominant modes of SSS variability. The first two, which have been discussed in previous studies, represent the seasonal and the interannual variations of the freshwater plumes over the continental shelf. The third mode of SSS variability, which has not been discussed hitherto, represents the salinity exchanges between the shelf and the deep ocean. A diagnostic study using floats and passive tracers identifies the pathways taken by the freshwater plumes. During the austral winter (JJA), the plumes leave the shelf region north of the BMC. During the austral summer (DJF), the plumes are entrained more directly into the BMC. A sensitivity study indicates that the high-frequency component of the wind stress forcing controls the vertical structure of the plumes while the low-frequency component of the wind stress forcing and the interannual variations of the RdlP discharge controls the horizontal structure of the plumes. Dynamical analysis reveals that the cross-shelf flow has a dominant barotropic structure and, therefore, the SSS anomalies detected by Aquarius represent net mass exchanges between the shelf and the deep ocean. The net cross-shelf volume flux is 1.21 Sv. This outflow is largely compensated by an inflow from the Patagonian shelf. © 2014. The Authors.

Menni R.C.,CONICET | Jaureguizar A.J.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | Stehmann M.F.W.,Ichthys Consultant | Lucifora L.O.,Dalhousie University | Lucifora L.O.,CONICET
Biodiversity and Conservation | Year: 2010

For more than a century, two major zoogeographic provinces have been proposed for the southwestern Atlantic: A warm water Argentinean Province from Rio de Janeiro (23°S, Brazil) to Valdés Peninsula (42°S, Argentina), and a cold water Magellanic Province from Valdés Peninsula to Cape Horn. This zoogeographic scheme has been recognized so far using data covering only parts of the whole geographic area. Here, we test the validity of this scheme by analyzing the distribution of sharks, skates, rays and chimaeras, using data from research cruises covering the entire area. We used cluster, similarity and dissimilarity analyses to identify species assemblages, and canonical correspondence analysis to identify the main environmental variables affecting the composition of the assemblages. The distribution of chondrichthyan assemblages strongly supports the current zoogeographic scheme and identifies a previously unknown and distinctive deep water zoogeographic unit off southern Brazil. Both, the Argentinean and Magellanic Provinces had extensive internal structure, with four and three subareas identified in each of them, respectively. These subareas correspond, with slight differences, to previously proposed zoogeographical districts within the Argentinean Province and confirm ecological differences within the Magellanic Province. Species composition had the highest correlation with depth and bottom water temperature. Since the distribution of anthropogenic disturbances in the region is uneven, different assemblages can be subjected to different impacts. Our results provide an objective basis to establish priority areas for the conservation of chondrichthyans in the southwestern Atlantic. © Springer Science+Business Media B.V. 2009.

Barbini S.A.,University of the Sea | Barbini S.A.,National University of Central Buenos Aires | Lucifora L.O.,CONICET | Lucifora L.O.,Centro Of Investigaciones Ecologicas Subtropicales Cies | Hozbor N.M.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero
Marine Biology Research | Year: 2011

Dietary shifts with size, maturity stage, season, and bottom type selection of Zapteryx brevirostris were evaluated, using generalized linear models. In terms of the index of relative importance, the most important prey were amphipods (39.17%), polychaetes (22.33%) and lancelets (20.33%), followed by decapods (8.93%), cumaceans (5.41%) and isopods (3.41%). Z. brevirostris consumed mainly polychaetes and amphipods in spring and summer, more cumaceans in winter, consumed more lancelets in spring, and preyed more heavily on decapods and isopods in summer. As Z. brevirostris increased in size, the consumption of decapods, polychaetes and isopods was higher, but the consumption of amphipods decreased. Mature individuals of Z. brevirostris consumed more lancelets than juveniles. Z. brevirostris selected sand over other bottom types. The diet of Z. brevirostris can be influenced by the selectivity of this species for sandy bottoms. As sandy bottoms are exposed to a high intensity of bottom trawling, the positive selection of sandy bottoms increases the vulnerability of Z. brevirostris by exposing it to fishing mortality. © 2011 Taylor & Francis.

Akselman R.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | Negri R.M.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero
Harmful Algae | Year: 2012

Azadinium spinosum has been identified as a species producer of azaspiracids (AZAs), marine toxins reported to cause human poisoning etiologically similar to diarrheic shellfish poisoning. AZAs are accumulated by molluscs via food web which, in turn, may cause human poisoning after consumption of contaminated shellfish. In this study, the presence of a species of the genus Azadinium, A. cf. spinosum, is reported for the first time in the Southwest Atlantic ocean, and two blooms in northern shelf waters of Argentina are analysed. Both blooms occurred during spring in succesive years and developed along extensive areas (up to 60km transection) of the middle shelf and near the shelf break in 1990, and also near the shelf break during 1991. The extended shelf break front of the Argentine Sea developed during spring and summer is a highly productive area rich in exploited marine resources. In November 1990, a first bloom (up to 9.03×10 6cellsL -1) produced heavy discolorations, and morphological and taxonomical studies showed that the causing organism was a new dinoflagellate genus. During September 1991 plankton composition and abundance along a transect from the coast to the Malvinas Current were analysed. Results showed that this dinoflagellate was the most important species in middle shelf waters, with high biomass and abundance values (up to 3×10 6cellsL -1) surpassing those of various chain-forming diatom Thalassiosira species, typical of the spring bloom. The description of this new taxon, according to the thecal analysis performed at that time by light and scanning electron microscopy, corresponds with little morphological differences to the thecal tabulation, cell morphology and dimensions of the recently described Azadinium spinosum. Taking into account these minor differences and due to the lack of both DNA sequence data and AZAs production, we decided to name it A. cf. spinosum. The phagotrophic dinoflagellate Gyrodinium fusus has shown to be an important grazer of A. cf. spinosum during the first bloom, suggesting that its grazing activity could have acted as a modeling factor in population levels of its prey. The presence of A. cf. spinosum in this area opens several questions as that related to toxin production given the regional importance of bivalve commercial fisheries. © 2012 Elsevier B.V.

The identification of marine macroalgae washed ashore provides valuable information on the composition of the nearby subtidal algal communities, and also to evaluate their applied potential. In the present study we report the quali-quantitative species composition of drift algae on the shores of three beaches during the 2012 and 2013 austral summers in Quequén, Necochea and Mar del Plata cities; all located on the southeastern coast of Buenos Aires province, Argentina. According to the relative biomass of the species, these algae were composed mainly by Dictyota spp. and Anotrichium furcellatum (J. Agardh) Baldock in Quequén; Dictyota spp., Jania rubens (L) Lamour and Corallina officinalis Linnaeus in Necochea and an unidentified Gigartinaceae, Rhodymenia sp., Ahnfeltiopsis sp. and C. officinalis Linnaeus in Mar del Plata.

Schejter L.,CONICET | Schejter L.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | Escolar M.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero
Pan-American Journal of Aquatic Sciences | Year: 2013

In this contribution we highlighted the importance of the gastropod Adelomelon ancilla (living and empty shells) as settlement substrate for the sea anemones Antholoba achates and Isotealia antarctica in soft bottoms of the SW Atlantic Ocean. Fifty percent of the sampled shells of A. ancilla presented at least one epibiotic anemone and up to a maximum of 6 anemones were reported in one living individual. Adelomelon ancilla shells are the first settlement substrate reported for I. antarctica. We also recorded the use of empty shells by Pagurus comptus and Propagurus gaudichaudii, as far as the less frequent record of other invertebrates and gastropod egg cases attached to the empty shells. These results are compared with the epibiotic organisms recorded on Odontocymbiola magellanica, another volutid species that shares the same habitat.

Favero M.,CONICET | Blanco G.,Instituto Nacional Of Investigacion Y Desarrollo Pesquero | Copello S.,CONICET | Pon J.P.S.,CONICET | And 4 more authors.
Endangered Species Research | Year: 2013

Seabird mortality associated with fisheries is one of the major threats leading to population decreases of certain species, particularly albatrosses and petrels. The present study was conducted to (1) analyze seabird bycatch in the Argentinean demersal longline fishery during the decade 2001 to 2010, (2) provide a baseline of the levels of incidental mortality prior to the implementation of the National Plan of Action-Seabirds, and (3) characterize in space and time the occurrence and intensity of seabird mortality. Fishing effort decreased from some 30 million to 5 million hooks set per year, and the overall bycatch rate for the whole period was 0.033 (0.019 SE) birds per 1000 hooks. The estimated total mortality for the 10 yr period was 7470 ± 2449 seabirds, the majority being black-browed albatrosses and white-chinned petrels. Seabird mortalities decreased by 1 order of magnitude towards the end of the decade, not due to lower bycatch rates but to a drop in the number of hooks set per year. The progress achieved so far in Argentina is important, but if seabird bycatch is to be reduced to negligible levels, it is imperative that the National Plan of Action-Seabirds is effectively implemented and that the longline fishery comply with the conservation measure calling for the use of mitigation methods that came into effect in 2010. Other management-related actions, such as the increase of capacities within the National Observer Program and the refinement of seabird sampling protocols, will have an effect not only in the longline but also in the large trawl fishery, where seabird bycatch has also been documented. © Inter-Research 2013.

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