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

DEPTH AND SIPHON CROPPING IN SCROBICULARIA
15 5 10 15 5
weight of remaining siphon (mg)
Fig. 4. I he depth of animal-137 io 38 mm) wilh different siphon weights measured during the 5 dav - after the) were buried (on Day Oi ,n .in
initial depth of 5.3 ± 0.4 cm I mean ± SD): ihe results of the five one-way analyses ol variance are given.
very variable, ranging from 5 to 18 mg in the 25 animals
dissected at the start of the experimenl and from
7 to 17 mg in the 11 animals with intact siphons used
as controls. It is clear that the animals losing 15 mg of
their siphon must have had an initial siphon weight
above the average weight.
To conclude, any regeneration during the experimenl
would have been negligibly small, so one can add
the weight of the remaining siphon to the amount cut
oil to estimate the original total siphon weight.
Siphon weight and burying depth
The burying depth of the natural population of Scrobicularia
during the experiment averaged 6 cm (n =
656 for the size class 35 to 39 mm). It was our intention
to bury all experimental animals at exactly the
same depth, but in practice a range of depth (± 1 cm)
was achieved.
Figure 3 shows the daily measurements of the
depth of a sample of animals during the course of the
experiment. Scrobicularia were able to change their
depth by 1 to 2 cm per day. Heavily cropped animals
moved nearer to the surface than the animals losing little
or no siphon. On the first day after the onset there
was already a large contrast between the burying
depths of animals with different siphon weights (Fig.
4). The divergence increased on the second day but re-
10 15 20
siphon weight (mg)
• Iree-living (CORE SAMPLING)
o experimental (THREAD METHOD!
Fig. 5. The depth (mean ± SE) of animals (37 io 38 mm) with different
siphon weight number per category (4 to 6. 7to9mg. and -o
on) is indicated; one-way analv-j- ol variance: R 2 = 35.4%; p <
0.001; also shown for comparison ihe relaiionship between depth
and siphon weight as measured in free-living annual- ot ihe same
-i/e (35 io 39 mm) in the summer (R* = 35.4%; p