Fróðskaparrit - 31.12.2000, Blaðsíða 103

TITTLEIKIN AV VANLIGASTU FØROYSKU DýRA- OG TARASLØGUNUM
A KLETTASTROND IMUN TIL YMISK UMHVØRVISVIðURSKIFTI
107
with tidal amplitude 0.4 m or less, which
were left out of the analysis by Bruntse et
al. (1999b), were explored.
Methods
Stations and data registration
The data set comprises abundance data of
hard-bottom littoral organisms from 168
sites in the Faroe Islands, as given in
Bruntse et al. (1999b). The data from each
station were collected from an 8 m wide
transect running from the upper to the low-
er part of the littoral zone. A sub zone for
each species, in which maximum abun-
dance occurred (approximately 1/10th of
the tidal amplitude), was selected and the
abundance estimated on a semi-quantita-
tive (ordinal) scale. The scale was modified
from Dalby et al. (1978). Only species that
were observed in at least 10% of the sites
were included in the analyses. These are
listed in Table 1. This sampling method is
designed to investigate species distribu-
tions along environmental gradients at in-
termediate spatial scales (e.g. in the Faroe
Islands) and should only with great care be
used for the analysis of biological interac-
tion and environmental variability on
smaller scales (e.g. within single station ar-
eas, see Discussion). For details on the
study area and sampling methodology, see
Bruntse et al. (1999b).
Environmental variables
The environmental variables included in
the analyses are listed in Table 2. The ex-
posure variable is calculated by using the
frequency of wind stronger than 15 m/s and
fetch to the nearest point of land i n each of
32 sectors. This variable is equal to the
Table 2. Environmental variables, their range, mean values and skewness for the 159 rocky shore sites with
tidal amplitude larger than 0.4 m.
Variable Definition Range Mean Skewness
Exposure Index based on map- and wind data. (l=lowest, 8=highest wave exposure) (1,2 8) 4.7 -0.1
Substrate l=bedrock; 2=boulders; 3=stones/rocks (1,2, 3) 1.1 3.8
Fjord index =D/W for fjord stations, where D=distance to open coast and W=width of fjord opening. =0 for open coast stations. (0-9.0) 0.8 2.9
Current l=no known strong current; 2=strong tidal current (1.2) i .2 1.3
Slope 1=<30°; 2=30-60°; 3=>60° (1,2, 3) 1.3 1.7
Tide Mean tidal amplitude (cm) (60-200) 107 0.8
Aspect 1=N, 2=E, 3=W, 4=S (1,2, 3,4) 2.4 0.0
Local protection l=no sheltering effect 2=physical shelter (skerry, foreland etc.) /(1, 2) 1.1 2.2