Estudio de las tramas tróficas asociadas a diferentes densidades de vieira Patagónica Zygochlamys patagonica del Atlántico SO mediante el uso de isótopos estables
Zygochlamys patagonica (King and Broderip, 1832) is an ecosystem engineer mollusk which forms aggregations or banks, of different densities, in the main frontal systems of the SW Atlantic Ocean. The objectives of this work were to analyze the composition, biomass, diversity and species richness of the benthic invertebrate assemblages at different scallop densities as well as the variability of their trophic webs at high and low scallop densities. For this, samples of the benthic invertebrate assemblages were taken at the Shelf Break Front with a non-selective epibenthic dredge. It was evaluated if the abundance (ind/m2) or biomass (colonial species, gr/m2) of the different taxa varied with scallop densities. The results showed that from 14 analyzed, the violet stars (Fam. Pterasteridae) and the epibenthic bivalve Hiatella meridionalis were the only species that had a positive correlation with the scallop density. The trophic web, analyzed by stable isotopes of carbon and nitrogen, showed that the scallop Z. patagonica was the base of the food web (as primary consumer) while the violet stars and the snail Adelomelon ancilla were the top predators. The sea urchin Sterechinus agassizi and the grey star Ctenodiscus australis presented higher ~d<sup>15</sup>N at low scallop densities probably due to a less herbivorous diet, product of hydrographic variations minor level. Z patagonica was an important prey of the snails A. ancilla and Fusitriton magellanicus, as well as of the sea urchin Austrosidaris canaliculata and the sea star C. australis. All these predators had higher percentages of scallops contribution in their diet in areas where scallops had higher densities. There were no differences between diversity and species richness of the benthic invertebrate assemblages at different scallop densities. These results indicate that the Patagonian scallop as an engineer ecosystem had, at small scales, both positive and negative effects on the benthic invertebrate assemblages, without increases diversity or species richness. This work allows insight into the role of the Patagonian scallop as an engineer ecosystem and how this species could influence a benthic trophic web.