We built Ecopath models (EwE), and evaluated the hypothesis that the overall primary productivity-rather than the ratio of large to small primary producers-constitutes an adequate proxy for predicting the amount of secondary and tertiary production and biomass (up to the fisheries). To evaluate this, we studied the productive patterns for large (micro) versus small (nano) phytoplankton in two south marine Patagonian ecosystems: The Inner Sea of Chiloe-ISCh and, Moraleda Channel-MCh. The size composition of primary producers is important for how energy is channeled through a food web and on to the higher trophic levels and eventually to fisheries. Arctic breeding migratory shorebird populations seem thus to encounter a predictable and abundant food supply at high southern latitudes on Isla Grande of Chiloé. The major contributor to zoobenthic biomass (Polychaetes) was indeed one of the main preys for the most abundant shorebird species at Chiloé. While total available biomass within each bay was similar during the three sampling years, the annual contribution of each class varied. Average biomass (4.4–9.6 g ash‐free dry weight m⁻²) falls within the values reported for temperate intertidal areas located at around 40°S latitude. Macrobenthic communities on Isla Grande of Chiloé are dominated by Polychaetes, Bivalves and Malacostraca. Here we provide an inter‐annual estimation of food supply at the southern limit of the Pacific temperate zone within a Site of Hemispheric Importance for the conservation of Arctic breeding shorebird populations during the nonbreeding season. On the southern Pacific coasts of South America, however, comprehensive information about macrobenthic assemblages at these habitats is lacking. Intertidal soft‐bottom assemblages located at high latitudes provide a critical food source for long‐distance migratory animals which link biodiversity across distant areas.
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