Food supply for waders (Aves: Charadrii) in an estuarine area in the Bag of Cadiz (SW Iberian Peninsula)

We studied the composition, density, size distribution and biomass of the food supply for waders in an estuarine area in the Bay of Cadiz (SW Iberian Peninsula), in winter (January-February) and in the pre-migratory period (late March). The estuarine area comprises an intertidal mudflat and an adjacent salina or salt-pan. On the intertidal mudflat, the biomass was 53 and 37 g AFDW.m(-2) in winter and the pre-migratory period, respectively. The main food source on mudflat was the polychaete Nereis diversicolor (44-54 % of the total biomass). On the other hand, the biomass in the salina was comparatively very poor, ranging from 0.008 to 0.079 g AFDW.m(-2) in winter and ranging from 0.011 to 0.09 g AFDW in late March. The main source of food in the salina was the crustacean Artemia. The total biomass on the mudflat during the pre-migratory period was 1.4 times lower than in February. This depletion could be caused by wader predation, mainly by Nereis diversicolor consumption. Although the potential food on the mudflats could allow high intertidal densities of waders, the availability of high tide foraging areas in the salina seems to contribute to the maintenance of these high intertidal densities. (C) 1999 Editions scientifiques et medicales Elsevier SAS.