Fróðskaparrit - 01.01.1999, Blaðsíða 192

196 RESPONSE TO WAVE EXPOSURE BY LITTORAL SPECIES IN THE FAROEISLANDS
This growth pattem may indicate that L. ar-
ticulata is favoured by the oceanic climate
in the Faroe Islands.
Other species were also observed in dif-
ferent growth pattems than found on most
other NE Atlantic shores. Laminaria digi-
tata was observed in abundance and was
common throughout exposure grades in the
Faroe Islands, whereas it was scarce in
sheltered areas in Norway (Kxuskopf and
Lein, 1997; Árrestad and Lein, 1993). On
north-west European coasts, amongst the
fucoids, Fucus serratus L. normally grows
lowest on the shore and above the laminar-
ians (Connor et al., 1996; Jorde, 1966). F.
serratus is very rare, however, in the Faroe
Islands. It is possible that in the Faroe Is-
lands, L. digitata occupies the space taken
by F. serratus on other coasts, thereby
reaching a broader distribution and greater
abundance on sheltered shores. Fucus ser-
ratus was reported in abundance along
most of the Faroese coasts by Landt (1800),
but since then has not been recorded until
recently (Lyngbye, 1819; Børgesen, 1905;
Irvine, 1982). The species was observed at
a few sheltered localities within one fjord in
1997. The plants were fertile in August
with both male and female plants present.
A contrasting situation exists in Iceland
where Fucus serratus has an abmpt north-
em distribution border in south-west Ice-
land. North of this limit, Ascophyllum no-
dosum, which normally grows immediately
above F. serratus, extends its vertical distri-
bution to cover the area occupied by F. ser-
ratus.
Effects of biological factors such as her-
bivory and predation are known to have a
large influence on species distribution and
the abundance of fucoid algae (for reviews,
see Chapman 1995). Predation may also
change along the gradient of wave exposure
as demonstrated by Robles (1997). The ab-
sence of Littorina littorea in the Faroe Is-
lands (see Sparck and Thorson (1933), who
mentioned only three finds of single indi-
viduals during the 1800s) is probably an
important factor for the abundance of some
species, compared to other North Atlantic
shores were it is an important grazer (Lein,
1980). In the Faroe Islands, Patella vulga-
ta seems to be the most important grazer
and was found throughout the exposure
scale in large numbers. In Norway, it is
generally abundant on moderately exposed
shores, but is found in smaller numbers on
both exposed and sheltered shores (Dalby
etal., 1978). The response curve for P. vul-
gata in Sogn and Fjordane County, howev-
er, resembles the even distribution ob-
served in the Faroe Islands (Kmskopf and
Lein, 1997). Hartnoll and Hawkins (1985)
demonstrated the tremendous effect of
grazing by Patella on semi-exposed shores
in the Isle of Man. Further experiments are
needed to evaluate the ecological influence
of P. vulgata on the development and stmc-
ture of littoral communities in the Faroe Is-
lands.
The species list (Table 4) reflects the he-
terogeneity of the exposed localities.
Crevices in cliff faces gave shelter to
species such as Rhizoclonium riparium and
Cladophora rupestris, which otherwise are
more frequently found in sheltered locali-
ties (Fig. 2). Localised shelter may also ex-
plain the occurrence of Fucus spiralis and