How the food supply harvestable by waders in the Wadden Sea depends on the variation in energy density, body weight, biomass, burying depth and behaviour of tidal-flat invertebrates

• Published in: Netherlands Journal of Sea Research
• Main Authors: Zwarts, L., Wanink, J.H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1993
• Subjects: OYSTERCATCHERS HAEMATOPUS-OSTRALEGUS; AMPHIPOD COROPHIUM-VOLUTATOR; MUSSELS MYTILUS-EDULIS; SCROBICULARIA-PLANA DACOSTA; KNOT CALIDRIS-CANUTUS; MARINE BENTHIC INVERTEBRATES; BIVALVE MACOMA-BALTHICA; REDSHANK TRINGA-TOTANUS; WADING BIRDS CHARADRII; NEREIS-DIVERSICOLOR; Midwinter; Calidris canutus
• Online Access: https://hdl.handle.net/11370/ef3998d7-fa89-4677-9686-8969a0c6678d; https://research.rug.nl/en/publications/ef3998d7-fa89-4677-9686-8969a0c6678d; https://doi.org/10.1016/0077-7579(93)90059-2

For several reasons, waders in the Wadden Sea face a large seasonal and annual variation in their food supply. Observations on a tidal flat in the Dutch Wadden Sea have shown that: (1) The average energy density of ten invertebrate prey species varies between 21 and 23 kJ.g-1 AFDW. In Scrobicularia plana and Mya arenaria, but not in Macoma balthica, the energy density is 10% lower in winter than in summer. (2) Depending on the species, body weights of prey of similar size are 30 to 60% lower in winter than in summer. (3) The year-to-year fluctuation in standing-crop biomass is larger in some species than in others, the difference depending mainly on the frequency of successful recruitment. The overall biomass of the macrobenthos in winter is half of that in summer, but the timing of the peak biomass differs per species. (4) The burying depth varies per species: Cerastoderma edule live just beneath the surface, while M. balthica, S. plana, M. arenaria, Arenicola marina and Nereis diversicolor bury more deeply and the majority of these prey live out of reach of the bird's bill. In all six species, burying depth increases with size. There is no seasonal variation in depth of C. edule and M. arenaria, but the four other species live at most shallow depth in early summer and most deeply in midwinter. Burying depths in winter vary from year to year, but are unrelated to temperature. Neither has temperature any effect on depth within months. For knot Calidris canutus feeding on M. balthica, the fluctuation in the accessible fraction was the main source of variation in the biomass of prey that is actually harvestable, i.e. the biomass of prey of suitable size that is accessible. Accordingly, the paper reviews the available data on the temporal variations in accessibility, detectability, ingestibility, digestibility and profitability of prey for waders. Only a small part of the prey is harvestable since many accessible prey are ignored because of their low profitability, while many profitable prey are inaccessible. The ...