The effect of southwestern Atlantic burrowing crabs (Chasmagnathus granulata) on habitat use and foraging activity of migratory shorebirds

FLORENCIA BOTTO; GABRIELA PALOMO; OSCAR IRIBARNE; MARIANO MARTINEZ

ESTUARIES

Año: 2000 p. 208 - 215

0160-8347

ABSTRACT: Southwestern Atlantic estuaries (Southern Brazil to Northern Patagonia, Argentina) are characterized by the presence of an intertidal burrowing crab Chasmagnathus granulata. This crab species is an important bioturbator which lives in large assemblages and excavates semi-permanent burrows that affect sediment characteristics. Our observations showed that distribution of the crabs in the Mar Chiquita coastal lagoon, Argentina (37_45_S, 57_26_W) affected habitat use and feeding success of migratory shorebirds. During the migratory season the two-banded plover (Charadrius falklandicus) foraged more frequently inside crab beds, and yellowlegs (Tringa flavipes and T. melanoleuca) fed more frequently outside crab beds. Focal observations on the feeding behavior of the white-rumped sandpiper (Calidris fuscicollis) and the two-banded plover inside and outside crab beds showed that the plover was a visual searcher and captured more prey inside crab beds, and the white-rumped sandpiper was a tactile feeder. Although consumption rates (prey min_1) did not differ between sites, their efficiency (prey probe_1) inside crab beds was less. These differences were probably related to changes in sediment characteristics and prey behavior, which vary with crab activity. Burrowing crabs alter the suitability of intertidal habitats used by shorebirds in southwestern Atlantic estuaries. We believe that the same process could be occurring with other burrowing crustaceans such as thalassinidean shrimps in other estuaries of the world and could have important implications for management of flats for shorebirds