Fróðskaparrit - 31.12.2000, Side 102

106
DOMINANT SPECIES ABUNDANCE RELATED TO ENVIRONMENTAL
FACTORS ON ROCKY SHORES IN THE FAROE ISLANDS
Introduction
Bruntse et al. (1999a,b) explored the re-
sponse to wave exposure of intertidal or-
ganisms in the Faroe Islands. They devel-
oped a biological exposure scale (cf. Dalby
et al., 1978) that was valid for rocky shores
with mean tidal amplitude larger than 0.4 m
• o t
using Expon software (Arrestad and Lein,
1993). Significant response curves were
obtained for 15 of the 23 dominant species
that were investigated. Biological zonation
patterns were also described. The results
confirmed earlier qualitative descriptions
of the distribution of littoral organisms in
the Faroe Islands, and comparisons were
made with the British Isles and the south-
west coast of Norway.
The biological exposure scale technique
utilises a reciprocal algorithm to develop,
alternately, response functions (polynomi-
als) for species abundance in relation to
wave exposure and exposure values for sta-
tions (Bruntse et al., 1999b). The method
relies on the presence of one factor, typical-
ly wave exposure, causing most of the
species variation. To test this assumption,
the data must be analysed by other meth-
ods, often Canonical Correspondence Ana-
lysis (e.g. in Kruskopf and Lein, 1997;
Bruntse et al.^ 1999a), and/or the results
may be compared to other studies of the
species response to the given factor.
Biological factors such as grazing and
predation are well known to have large ef-
fects on the distribution of littoral species
on local as well as larger spatial scales (Un-
derwood and Chapman, 1996; Chapman,
1995). Bruntse et al. (1999b) discussed
possible effects on the littoral community
Table 1. Species used in the analysis and their
abbreviations as used in Figs. 1-5. Algae
Agl sep Aglaothamnion sepositum (Gunnerus) Maggs & Hommers.
Alaria Alaria esculenta (L.) Grev.
Asco Ascophyllum nodosum (L.) LeJol.
Clad ru Cladophora rupestris (L.) Kiitz.
Corall Corallina officinalis L.
F dis an Fucus distichus L. ssp. anceps (Harv. & Ward ex Carruthers) Powell
F evan F. evanescens C. Agardh
F spir F. spiralis L.
F ves F. vesiculosus L.
Him el Himanthalia elongata (L.) Gray
La dig Laminaria digitata (Huds.) J.V. Lamour.
Masto Mastocarpus stellatus (Stackh. in With.) Guiry in Guiry et al.
Palm Palmaria palmata (L.) Kuntze
Pelv Pelvetia canaliculata (L.) Decne. & Thur.
Pol str Polysiphonia stricta (Dillwyn) Grev.
Porph Porphyra umbilicalis (L.) J. Agardh Lichen
Verr Verrucaria mucosa Wahlenb. Invertebrates
Li obt Littorina obtusata (L., 1758)
Myt ed Mytilus edulis L., 1758
Nucel Nucella lapillus (L., 1758)
Patel Patella vulgata L., 1758
Semiba Semibalanus balanoides (L., 1767)
of competition between species of algae
and of grazing by Patella. The main aim of
our study, however, was to use in part the
same data set to investigate the relative im-
portance of wave exposure and other abiot-
ic environmental factors on rocky shore
communities in the Faroe Islands and to
analyse the nature of the unexplained vari-
ation. The species response curves devel-
oped using Expon by Bruntse et al. (1999b)
were interpreted in view of the new analy-
ses. In addition, the data from the stations