waders and their estuarine food supplies - Vlaams Instituut voor de ...

Burying depth as a compromise between feeding
and predation avoidance
Siphon length in Scrobicularia and Macoma increases
with shell size (Figs. 1 and 2). Scrobicularia use their
longer siphon to increase both their burying depth and
feeding radius (Fig. I) Feeding radius also uvjy
with shell size in Macoma. but larger animals reduce
their burying depth (Fig. 2), which means that larger
Macoma use an increasing proportion of the siphon
length for deposit feeding. A decrease of burying
depth with size had already been found in Ihe firs!
3-40
1 20
60.(1}
FEEDING RADIUS. BURYING DEPTH AND SIPHON SIZE
siphon weight (mg)
study on burying depth of Macoma (Hulscher 1973).
However, burying depth is independent of size in Macoma
larger than 10 mm when all field dala. collected
during seven summer periods, are taken together
(Zwarts & Wanink 1989). When the dala are analysed
according lo sampling date, lite relation is usually positive
and sometimes, especially in spring and summer,
negative (Zwarts unpubl.).
The calculated relationships between siphon length
and siphon weight may be used to estimate the feeding
radius of individual Scrobicularia and Macoma of
T—i—i—i——i—i—i—r
rj> •$ •**> •$ jJ^J^JJJJ^ rip *$> .Cl ,$> ^^J^J^jl
jJjV^J^*!^ ,£.$>.$>.$> rij) N") \"1 \0
'&y 1* "&'&* - , * *&'&* J
deviation Irom average body weight (%)
c yy ^ *yy - 1 '
Fig. 10. A. Bun, ing depth (cm) and estimated feeding radius (cm) in Scrobicularia I35-39 mini U a function ofbod) condition m animals null
different siphon weights. Body condition is expressed as per cent deviation from average body weighl. Feeding radius equals siphon lengih
i using ihe apiMion in Fig 9 in enliven siphon weighl lo siphon length) minus nursing depth (from Fig. 10 in Zwarts 1986). The graph is based
on 3062 individuals collected in summer, lor more details see Zwarts (1986). Animals living below the danger line of 6 cm arc out of reach of
Ihe main predator, the Owcic.it.. her B. I ceding radius as per cent of the siphon length as a funclion of body condition, using the dala from the
upper panel.
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