MEPS 178:229-240 (1999)  -  doi:10.3354/meps178229

ABSTRACT: Evaluation of the importance of different benthos communities as feeding sites for waders and waterfowl is not only fundamental for understanding feeding ecology, it also enables the prediction of the effects of habitat loss. However, detailed analyses of the importance of different benthos communities for waterbirds are scarce, particularly for the German Wadden Sea. In the early 1990s, backbarrier tidal flats of the East Frisian Wadden Sea were dominated by Lanice conchilega. To estimate the relevance of those flats for waterbirds during autumn migration 1994, number, distribution and food consumption of the 7 most abundant bird species on these flats (oystercatcher, curlew, dunlin, redshank, common gull, black-headed gull, herring gull) were investigated on 2 different types of L. conchilega dominated flats (Lanice flat, Undulating flat). Spring tide counts throughout 1994 showed maximum bird numbers during spring (maximum: 56000 birds) and autumn migration (maximum 111000 birds). Of the 7 species examined, 4 species (oystercatcher, curlew, redshank, common gull) used both flat types in higher densities than expected. Whereas common gulls preferred the Undulating flats, oystercatchers preferred the Lanice flats. The overall number of macrozoobenthos organisms varied between 3360 and 5520 m^-2 on the Undulating flat, and between 8520 and 15100 m^-2 on the Lanice flat. Correspondingly, the estimated biomass ranged from 67.6 to 142.3 g AFDW m^-2 and 128.4 to 337.2 g AFDW m^-2 (AFDW: ash free dry weight), respectively. Therefore, biomass was higher than in most other Wadden Sea areas. The most abundant species were Heteromastus filiformis, L. conchilega, Macoma balthica and Mytilus edulis. The overall consumption of the 7 bird species studied (70% of all waterbirds present) decreased from 16.6 g AFDW m^-2 in August to 12.3 g AFDW m^-2 in October. Assuming a similar consumption for the remaining 30% of the birds, overall consumption would have ranged between 17.6 and 23.7 g AFDW m^-2. Due to the high biomass of the standing stock, relative consumption (5.2 to 13.7 %) was similar to other regions of the Wadden Sea. Only 3 species (oystercatcher, curlew, common gull) consumed between 78 and 93% of the overall consumption of the 7 species examined. Whereas waders mainly foraged on the accompanying fauna of the L. conchilega community, the bulk of the diet of gulls was L. conchilega itself. In general, food supply on L. conchilega dominated flats can be judged as favourable. However, the possibility that food consumption could have been a limiting factor, at least for some species (e.g. oystercatcher), cannot be ruled out.

KEY WORDS: Charadriiformes · Feeding ecology · Food consumption · Macrozoobenthos · Phenology