Fróðskaparrit - 01.01.1995, Page 100

104
PARASTENOCARIS GLACIALIS IN THE FAROEISLANDS
fauna, but has entered from the free water
outside the beaches. Parastenocaris gla-
cialis seems to be the only truly interstitial
species in these assemblages.
In most of the small beaches only a few
specimens of P. glacialis were found, while
the beaches at Sørvágsvatn (Skjatlá and es-
pecially Sørvágsvatn at Ivarsheyggjur)
contained dense populations. Possible fur-
ther studies on this unique fauna should
preferably concentrate on these beaches
and this lake.
Discussion
As mentioned above, P. glacialis may be
found in very small water bodies lacking
in- and outlets, and also high up in the
mountains in Fennoscandia. Apparently the
species is limited to the northem parts of
Europe (and probably Asia) and is adapted
to cool-temperate conditions. The ability to
disperse is low among the Parastenocaris
species (as evidenced by the distribution of
P. phyllura in Fennoscandia, Enckell,
1969). Resting stages are not known from
any species and the means of dispersal are
unknown. A single species has been repor-
ted from plankton, so dispersal in open wa-
ter seems unlikely. Dispersal upstream in a
water course may be possible in the hy-
porheal habitat (Tilzer, 1968). Moreover,
species restricted to ífesh water, like P.
glacialis, must have greater difficulties to
disperse than species able to occur in
brackish water (e.g., in the Baltic).
It appears that some moss- and plant-liv-
ing harpacticoid species have resting stages
facilitating dispersal. One Parastenocaris
species (P. brevipes) is found both in
Sphagnum bogs and in subterranean habi-
tats.This might indicate that the ability to
form resting stages is not completely ab-
sent in the genus. Possibly the occurrence
on isolated islands like Iceland, Spitzber-
gen and the Faroes in the north, and Tene-
rife and New Caledonia in the south
(Noodt, 1968) indicates such a possibility.
The period of ice recession after the last
Ice Age was characterized by meltwater
streams and rivers, and dammed lakes
(Brinck, 1966). The periglacial fauna - to
which P. glacialis probably belonged - con-
tained eurythermal and cold-stenothermal
species. Bare sandy and gravelly surfaces
were common. These areas, which were ex-
tensive in the protocratic era during the ice
regression, exist i.e. as sandy beaches to-
day. An opportunistic species might very
well have followed the retreating ice to-
wards the north in Fennoscandia (e.g., P.
glacialis). Likewise the species might have
rafted on ice floes on the surface fresh wa-
ter following the break-up of the ice-en-
crasted sand/gravel/soil to islands in the
North Atlantic, like the Faroes (see En-
ckell, 1988, for a discussion of this possi-
bility)
This type of dispersal presupposes a tole-
rance to low temperatures. Many interstitial
animals endure freezing, and Jansson
(1968) reported living animals in samples
of frozen sand from the Baltic (including
Parastenocaris phyllura). Enckell (un-
publ.) found both P. phyllura and P. gla-
cialis in samples of frozen sand from
Swedish lakes and the specimens survived
the melting of the ice. These two species
are also regularly found under the ice in the