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Daponte M.C.,University of Buenos Aires | Calcagno J.A.,University of Buenos Aires | Calcagno J.A.,CONICET | Acevedo-Luque M.J.J.,University of Buenos Aires | And 5 more authors.
Bulletin of Marine Science

Salps and chaetognaths constitute an important fraction of the macrozooplankton and have a prominent role in the marine food web. In our study, we analyzed the species composition, density, and biomass in an area of the southern Atlantic Ocean during the austral winters of 1999, 2000, and 2001. The most abundant and frequent species were the salpids Ihlea magalhanica (Apstein, 1894) and Iasis zonaria (Pallas, 1774), and the chaetognaths Parasagitta friderici (Ritter-Zahony, 1911) and Serratosagitta tasmanica (Thomson, 1947). Chaetognaths were found in over 80% of the stations throughout the three winters, reaching up to 67 individuals (ind) m -3. Salps were found surviving at low population densities in 2000 and 2001, but in 1999, there were mass occurrences of I. zonaria and I. magalhanica, reaching densities of 301 and 123 ind m -3, respectively. To estimate biomass in C units, the relationship between dry weight and size was calculated for S. tasmanica and for solitaries and aggregates of I. zonaria and I, magalhanica. The biomass of salps and chaetognaths (as mg C m -3) over the shelf during the three consecutive winters was strongly related to prevailing physical and biological conditions. In 1999, the greatest contribution to macrozooplankton biomass corresponded to salps, while in 2000 and 2001, chaetognaths dominated the biomass. In swarm conditions, like in 1999, I. zonaria and I. magalhanica widely dominated over copepods and chaetognaths, producing an increase in the quantity of available C of up to 60 times in relation to the periods with very low population densities. © 2011 Rosenstiel School of Marine and Atmospheric Science. Source

Mauna A.C.,Institute Nacional Of Investigacion Y Desarrollo Pesquero Inidep | Botto F.,CONICET | Franco B.,Servicio de Hidrografia Naval SHN | Schwartz J.M.,Institute Nacional Of Investigacion Y Desarrollo Pesquero Inidep | And 4 more authors.
Journal of Sea Research

Marine benthic trophic relationships and food web structures may be influenced by benthic-pelagic coupling processes, which could also be intensified by the physical dynamics of marine fronts. In this work, we employed stable isotope (δ13C and δ15N) analysis to investigate the influence of the Southwest (SW) Atlantic shelf-break front (SBF; 38-39°S, 55-56°W; Argentina) on an epibenthic trophic web. Epibenthic organisms were sampled, at depths of ~100m, with a non-selective dredge from a sandy bottom community located in frontal (F) and marginal (M) areas. The SBF position and the chlorophyll-a (chl-a) concentrations were inferred using satellite data of the sea surface temperature (SST) and satellite chl-a concentration, respectively. The most noticeable shifts in stable isotopes between the sampled areas were those of the Patagonian scallop, Zygochlamys patagonica (δ13C), and those of the sea urchin, Sterechinus agassizi (δ15N). Diet analyses inferred from stable isotopes and mixing models demonstrated that the dominant component of this community, Z. patagonica, had variable contributions to higher trophic levels between areas. More importantly, the epibenthic assemblage in F areas showed δ13C-enriched and δ15N-depleted isotopic signatures with respect to the M areas. Collectively, this evidence suggests that frontal dynamics promotes the accumulation of δ13C-enriched phytoplankton in the seabed in F areas, while in M areas the more degraded organic matter becomes more important in the trophic web, decreasing the δ15N isotopic signature of the assemblage. Therefore, the trophic web was sustained by fresher food in F areas than in M areas, demonstrating the role of frontal dynamics in the shaping of these communities. © 2011 Elsevier B.V. Source

Souto V.S.,CONICET | Souto V.S.,Institute Nacional Of Investigacion Y Desarrollo Pesquero Inidep | Schejter L.,CONICET | Schejter L.,Institute Nacional Of Investigacion Y Desarrollo Pesquero Inidep | And 2 more authors.
American Malacological Bulletin

Aequipecten tehuelchus (d'Orbigny, 1846) is a commercial resource, distributed from Rio de Janeiro (Brazil) to Golfo Nuevo (Argentina), on sandy and muddy bottoms. In Argentina, the major banks of exploitation are located in the gulfs of San José and San Matías. This study represents the first ecological study of A. tehuelchus in shelf waters off Buenos Aires, Argentina. Eighteen epibiont taxa were registered on the individuals analyzed. Polychaetes were the most frequent epibiotic organisms (82%), including Serpulidae (Rafinesque, 1815), Phyllochaetopterus socialis (Claparède, 1869), Idanthyrsus armatus (Kingberg, 1807) and Chaetopterus antarcticus (Kingberg, 1866). Ostrea puelcheana (d'Orbigny, 1842), Balanus cf. amphitrite (Darwin, 1854) and solitary ascidians were found on less than 30% of the sampled individuals. Bryozoa and Porifera were scarcely represented. Phyllochaetopterus socialis, I. armatus and Balanus cf. amphitrite were most frequent on the upper (left) valve. This study nearly doubles the number of epibionts identified and mentioned on A. tehuelchus in Patagonian Gulfs. Three individuals of the commensal pea crab Tumidotheres maculatus (Say, 1818) were found inside three different specimens of A. tehuelchus. One left scallop valve was burrowed into by the parasitic polychaete Polydora (Bosc, 1802). Source

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