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SEASONAL VARIATION IN BODY WEIGHT OF BIVALVES
SEASONAL VARIATION IN BODY WEIGHT OF THE BIVALVES
MACOMA BALTHICA, SCROBICULARIA PLANA, MYA ARENARIA AND
CERASTODERMA EDULE IN THE DUTCH WADDEN SEA
The paper deals with the seasonal and annual variations in the weight of the soft parts of four bivalve species,
Macoina balihica. Scrobicularia plana, Mya armaria and Cemsiodernui edule from tidal flats of
the Dutch Wadden Sea. The paper reviews methodology and points to error sources. The variation in ashfree
dry weight (AFDW) between individuals of the same size collected at the same time and place could
be attributed to age, parasitic infestation, gametogenesis. burying depth and siphon size. The allometric
relations between weight of soft parts and size are given in equations, averaged per month.
The body weight of all four bivalve species peaks in May and June at a level approximately twice
the lowest value, which occurs in November to March. The extent of this seasonal fluctuation varies,
however, from year to year. The presence of gametes explains a part of the peak weight in summer. The
winter loss of body weight is less at low temperatures, due lo reduced energy expenditure when the animals
are inactive. No large differences were found between the seasonal change in body weight in the
Wadden Sea and elsewhere in the temperate zone.
Introduction
Large seasonal variations occur in the biomass of
macrozoobenthic animals living on intertidal Bats in
the temperate /.one. Taking all species together, their
biomass in the Wadden Sea is twice as high in summer
as in winter (Beukema 1974). As has been well documented
in the tellinid bivalve Macoma balihica (L.).
this difference is partly due to summer recruitment,
but predominantly results from somatic growth in late
spring and early summer and loss of weigh! later in the
season (Lammens 1967. Beukema 1982b. Beukema &
Despiez 1986. Beukema el al. 1985, Essink & Bos
1985).
Somatic growth of bivalves can be considered in
two components: an increase in shell si/e and an
improvement in body condition, i.e. a change in flesh
weight at constant shell size. The seasonal variation in
body condition has important implications for predators,
such as wading birds Charadrii. which depend on
the macrozoobenthos. For them, a reduction in flesh
content must be compensated by a corresponding
increase in the number of prey captured if the same
food consumption is to be maintained.
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As part of a study on the interaction bet*
waders and their fcxxl supply, this paper describes the
seasonal and annual fluctuations in the flesh content of
four bivalve species. Macoma balihica, Scrobicularia
plana (Da Costa), Mya arenaria (L.) and Cerastoderma
edule (L.). It is shown thai ihe magnitude in the
seasonal variation differs between these species and
from year to year. The four species contribute a major
share to the total biomass of the macrozoobenthos in
the Wadden Sea. with exception of Scrobicularia
(Beukema 1976). Scrobicularia was locally, however,
an important species, contributing one quarter to the
total benthic biomass (Zwarts 1988b).
Methods
Area
Animals were sampled over 11 years. 1976 to 1986. in
the Dutch Wadden Sea along the mainland coasts of
the provinces Groningen