Fróðskaparrit - 01.01.1999, Blaðsíða 178
182 RESPONSE TO WAVE EXPOSURE BY LITTORAL SPECIES IN THE FAROEISLANDS
on moderately exposed shores. A biological exposure
scale was developed for the area based on the response
curves for these 15 species. The scale is valid for rocky
shores in the Faroe Islands with mean tidal amplitude
larger than 0.40 m, and can be used to account for the
distribution of dominant and frequently occurring
species in the littoral zone. This is supplemented with
diagrams illustrating the vertical distribution and abun-
dance of species at localities selected to represent dif-
ferent wave exposure. Our studies confirm the descrip-
tions of the distribution of littoral organisms in earlier
works about the Faroe Islands. Compared to the British
Isles and the south-west coast of Norway, the most strik-
ing differences are the abundant growth of Laminaria
digitata and Alaria esculenta on sheltered shores, the
lack of dense populations of Fucus serratus and the fre-
quent occurrence of many species over the whole expo-
sure range.
Introduction
Previous studies of the littoral marine algae
and invertebrates of the Faroe Islands have
focused either on the occurrence of species
and their distribution or on qualitative de-
scriptions of communities (Børgesen,
1902; 1905; Lemche, 1929; Stephensen,
1929; Sparck and Thorsen, 1933; Høpner
Petersen, 1968; Irvine, 1982; Price and
Famham, 1982; Tittley et al., 1982).
Wave action is known to affect plant and
animal communities on rocky shores, but
wave exposure is difficult to calculate from
physical data in areas of complicated ba-
thymethric conditions. Several researchers
have developed scales for assessment of ex-
posure based on species composition
changes in relation to wave exposure (e.g.
Crisp and Southward, 1958; Ballantine,
1961; Dalby etal., 1978). There is a risk of
the reasoning becoming circular when bio-
logical aspects are interpreted in terms of
biological exposure values, as pointed out
by Raffaelli and Hawkins (1996). How-
ever, when used with caution, such scales
may be useful in describing changes in
rocky shore communities in relation to
wave exposure, provided it is the predomi-
nant environmental variable. In the present
work, a biological exposure scale is devel-
oped for the hard-bottom communities of
the Faroe Islands. The scale is used to ac-
count for the distribution of dominant and
frequently occurring species in the littoral
zone. This is supplemented with informa-
tion on the vertical distribution and abun-
dance of species at nine localities selected
to have different wave exposure values.
Study Area
The Faroe Islands is situated in the North
Atlantic between 61°33’ and 62°40’N and
6°25’ and7°68’W (Fig. 1). Amajorpartof
the shoreline consists of basaltic bedrock.
The tidal amplitude varies within short ge-
ographical distances, being virtually non-
existent in the Tórshavn area (not included
in our study), and reaching approximately
2.5 m in the outer parts of the islands to the
west. Water temperature ranges from a
monthly average of 6°C in February to
10°C in October and air temperature from
4°C in February to 11 °C in August (Lys-
gaard, 1969; Hansen, 1997).
Materials and Methods
The exposure scale was developed accord-
ing to the technique described by Dalby et
al. (1978) and calculated utilising Expon
software (Árrestad and Lein, 1993). The
technique uses a reciprocal algorithm to de-
velop, altemately, response functions
(polynomials) for species in relation to