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

shell sue: 32.4 mm
siphon; 125-r.ll.9mg
6 7
day
FEEDING RADIUS, BURYING DEPTH AND SIPHON SIZE
Scrobicularia plana Macoma balthlca
shell size: 296 mm
slplw 13.3-.12.I mg
6 7 8
day
8
7
6
4
3
2
shell sue. 18 7 mm
U siphon: 18-*1.3mg
1 -
6 7
day
shell size: 186 mm
siphon. 1.8-.2.2
8 5 6 7 8
day
Fig, 4. Siphon length lem) ol 2 Scrobicularia and 2 Macoma measured from 5 days lo » days after burial. Shell size, siphon weight (AFDW)
before and after cropping and lime of cropping I < I are indicated.
than animals that had lost little or no siphon, just as
found in similar experiments with Scrobicularia
(Zwarts 1986). The burying depth increased with the
weight of the remaining siphon and. as Fig. 5 shows,
the relationship between siphon weight and depth was
similar for the cropped animals and the controls. Sta-
o.
&
o
£ 3
0 0.5 1.0 1.5 2.0 2.5
siphon weight (mg)
Fig. 5. Burying depth (cm) as a function of siphon weight of Ma­
coma (16-17 mm) on a mudflat in May 1986 (n = 61). Except 17
controls, between 20 and 70% of the siphon weigh! has been re­
moved shortly before ihc depth measurements were done.
119
listical analyses confirmed that burying depths were
highly correlated to the weight of the remaining siphon
and that the weight of the amount thai had been cut oil
did not add significantly to the explained variance.
Siphon length and siphon weight
Siphon length was 0.2-0.5 cm in Macoma and 0.5-2.0
cm in Scrobit tilaria after the siphons had been cut olT
in the animals killed in boiling water. These ranges
correspond well wilh the measurements of Hodgson &
Trueman (1981) and Pekkarinen (1984). In both
species, the length of the dissected siphons, as well as
the weight per cm of siphon, was highly correlated
with shell length (Table 1). Also, the relationship
between the dissected lengih and the maximum length
of the extended siphon, measured in the same (still
living) Scrobicularia. was highly significant (r = 0.64.
p < 0.0001). The extended siphons were ten times as
long as the dissected siphons, as also found by Hodgson
& Trueman (1981). To investigate the relationship
between siphon weight and siphon length independently
of shell si/e. dissected siphon lengths and
siphon weights were expressed as deviation from the
average values ot the corresponding si/e classes, using
regression equations given in Table I. The relation between
siphon weight and dissected siphon length was
DO) linear bin curvilinear (Fig. 6).