Náttúrufræðingurinn - 1985, Page 11

SUMMARY
Sediment reworking by
Yoldia hyperborea Loven
in Hvalfjördur, SW-Iceland.
by
Vigfús Jóhannsson
Insitute of Biology,
University of Iceland,
Grensásvegur 12,
Reykjavík.
Yoldia hyperborea is common at the depths
from 10—200 m in the fjords on the west, north-
west, north and east coasts of Iceland (Spárck
1937, Arnþór Garðarsson et al. 1972, Bogi Ingi-
marsson and Árni Heimir Jónsson 1973, Kristín
Aðalsteinsdóttir and Arnþór Garðarsson 1980).
This clam is an infaunal member of the benthic
community in Hvalfjörður, SW-Iceland. The
distribution of Yoldia hyperborea is known from
two areas in Hvalfjördur (fig. 3).
In Area A the number of Yoldia per m2 was
7—85. The average nuntber of this species at
Station 1 was 55/m2 and at Station 2 44/m2 (fig.
4) (Kristín Aðalsteinsdóttir and Arnþór Garð-
arsson 1980). The average number of Yoldia
hyperborea in Area B in Hvalfjörður (Fig. 5)
was 13/m2 (Bogi Ingimarsson and Árni Heimir
Jónsson 1973).
Yolda hyperborea is a deposit-feeder.
Sediment is conducted to the mantle cavity by a
pair of feeding palps. The particulate matter is
sorted into a small edible fraction and a iarger
fraction that is rejected through the siphons
(Drew 1899). The feeding position of Yoldia
hyperborea is shown in fig. 1. Measurements of
hourly reworking rates were made under cont-
rolled temperature condition. Only specimens
from Area A in Hvalfjördur were used in exper-
iments. The results were used to estimate the
annual sediment reworked in Area A in Hval-
fjördur by Yoldia hyperborea. Fig. 6 gives the
average rate of sediment reworking at controll-
ed tremperature. The sediment reworking per
clam ranged from 0,013 ml/hr at 0°C to 0,039 ml/
hr at 6°C. The volume of sediment reworked
yearly by Yoldia hyperborea in Hvalfjördur was
estimated 240 ml per clam. Table I gives the
estimated monthly reworking of sediment on
Stations 1 and 2.
The total weight of sediment reworked yearly
by Yoldia hyperobore in Area A (30 km2) in
Hvalfjördur was estimated around 25,000 tons.
No direct nieasurements were made on the
changes of the sediment during the feeding of
Yoldia hyperborea. But it was clear that the
texure of the sediment was altered, mainly by
increasing number of faecal pellets. The lenght
of the faecal pellets was around 1 mm.
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