Náttúrufræðingurinn - 1980, Side 26

Ingótfsson, Agnar. 1977. Distribution and
habitat preferences of some intertidal
amphipods in Iceland. Acta Naturalia
Islandica 25: 1—28.
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(Crustacea: Isopoda). Líffræðistofnun
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lífsferli þanglúsa af ættkvíslinni Jaera
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within the superspecies Jaera albifrons
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SUMMARY
Distribution and habitat
preferences of Jaera spp.
(Isopoda: Asellota) in Iceland
by Agnar Ingólfsson,
Institute of Biology, Umversity of Iceland,
Grensásvegur 12, Reykjavík.
vertical intervals of 50 or 25 cm. The samp-
led area at each station was 800 cm2. All
algae were removed and searched for
animals in the laboratory.
The species Jaera ischiosetosa, J. albifrons
and J. prehirsuta were found on all coasts.
Large stretches of the south coast of Iceland
are, however, unsuitable for these animals.
On shores dominated by fucoids J. prehirsuta
was the commonest species in southwestern
Iceland. Moving clockwise arount the coast
into cooler waters J. albifrons becomes com-
mon in the northwest, and J. ischiosetosa in
the north and especially in thc east, where /.
prehirsuta has become relatively rare (Table
I).
J. ischiosetosa is frequently found under
brackish conditions, in lagoons, brackish
ponds and estuaries; and in southwestern
Iceland it is exclusively found under such
conditions. The other two species are con-
fined to shores dominated by fucoids, and /.
ischiosetosa is common on such shores also on
northern and eastern coasts. Here this
species is about equally common on very
sheltered Ascophyllum shores, the somewhat
more exposed Fucus vesiculosus shores, and the
exposed Fucus distichus shores. The other two
species seem to prefer the more sheltered
shores, although this tendency is not signifi-
cant for /. prehirsuta (Table II). All species
reach peak abundance in the middle shore
region on shores dominated by fucoids,
although the peak of /. prehirsuta occurs a
little lower than that of the other two species
(Fig. 1). The species are frequently found
together, especially in northern Iceland, and
it is not unusual to find all three species in
the same 20X20 cm quadrat. On shores
with fucoids all species are more commonly
found on algae than on or under stones. J.
prehirsuta shows this tendency to a greater
extent than the other two (Table III). The
density of / ischiosetosa and J. prehirsuta on
shores dominated by fucoids is on the aver-
age much greater than that of J. prehirsuta.
Thc density of J. prehirsuta is comparatively
low, even on southwestern shores where the
other two species are rare.
Data from a large number of shore tran-
sects from Iceland were analysed. At each
transect samples were taken from stations at
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