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

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• INFESTED
O UNINFESTED
88 7.2 7.5 90 91 11.6 100%
M 0 N
Fig. 6. AFDW (± SE) of ilie Sofl pans of Macoma 15 mm lone
during 1986. with a distinction made between uninlesied and those
iiut were infested b) the trematode Parvatrcma affinis. The SE of
the uninlesied indiv iduals was always less than 0.5 mg and so could
not be indicated. The percentages along die lower border indicate
the degree of infestation of the population A two-way analysis ol
variance reveals that month and infeation explain • MI'IIII'H .mi pan
of Ihe variance iR-' = 0.32 and 0.04, respectively*. Since the
interaction term is also Hgnifinrnt, the differences in weight
between the infested and uninlesied animals are not equal for each
month; n = 2726.
laria calculated from 45 equations for which r > 0.99.
with slope and intercept ± SE. is:
ln(mg) = 2.900 ± 0.089 ln(mm) - 5.044 ± 0.322.
Both the slopes and the intercepts for Macoma
reached a minimum in early spring and a maximum in
late sinnmer. The slopes and intercepts for Mya and
Cerastoderma were low in May-June and remained
high in autumn and winter. Essink (1978) found
differences in the value of the slope of Cerastoderma
between the years, but no seasonal variation.
The body weight of all species was low in February
and March and high in May and June (Fig. 8). The
seasonal variation in body weight of Mya and
Cerastoderma was 1.5 limes larger in the smaller size
classes than in the larger ones. This large difference
did not occur in Macoma. in which the small animals
SEASONAL VARIATION IN BODY WEIGHT OF BIVALVES
35
Fig. 7. The relative si.mdard deviation iKSL): standard deviation as
percentage Of the mean ± SKI of the AI-'DW of ihe soli pails of
Scrobicularia during the course of the year. The one-way analysis
of variance shows that the RSD differs per month iK = 030,
p < 0.001. n = 139). The RSD was calculated over 139 si/e classes
for which the AFDW was known in at least 5 individual specimens
which were collected on the same dale and ihe same spol.
Tabic 6. Macoma. Average slope lb ±SE) and average intercept (a
± SE) per month of the regression lnimg AFDW of ihe sofl pots)
against In (mm length). Regressions are selected for which r>0.99.
The slopes differ significantly per month IR-' = 0.28. p