An invasive intertidal reef-forming polychaete affect habitat use and feeding behavior of migratory and locals birds in a SW Atlantic coastal lagoon

The objective of our research was to evaluate by sampling and field experiments the effects of the invasive intertidal reef-building polychaete Ficopomatus enigmaticus on the habitat use and foraging behavior of birds in Mar Chiquita coastal lagoon (37°40′S, 57°23′ W, Argentina). Nearby areas with and without reefs were selected to asses their use by birds. Focal observations during low tide showed that bird densities (migratory shorebirds = Tringa melanoluca, T. flavipes, Calidris fuscicollis; non-migratory birds = Phalacrocorax olivaceus, Larus dominicanus, L. maculipennis, Anas spp., Vanellus chilensis, Milvago chimango) were higher on reef surface compared with similar areas without reefs. Migratory shorebirds used reefs surface mainly for feeding, while local birds used it for resting. Foraging rates of T. melanoleuca and T. flavipes were higher on the reefs than in the bare sediment. Comparative sampling (10 core per site) showed that epifaunal organisms (amphipod Melita palmata, crab Cyrtograpsus angulatus and gastropod Heleobia spp.) were more abundant on reef surfaces, but the density of infaunal preys (the polychaetes Laeonereis acuta, Nepthys fluviatilis, and Neanthes succinea) were not different between areas. Bird exclosure experiment and control (n = 10) showed no differences in density and size distribution between treatments for any benthic species analyzed. In conclusion, there was a positive effect of F. enigmaticus reefs on the habitat use of birds, because this area was preferred for feeding and resting, and there were more epifaunal preys which positively affected the foraging rates of shorebirds.