Fróðskaparrit - 01.01.2007, Síða 153

BOTNDÝR í BLEYTBOTNl Á FØROYSK.UM FIRÐUM
151
It is well known that benthic communi-
ties are characterized by a large number of
rare species and dominated by only a few
species (Gray, 1981). Table 3, 4a and 4b
show a ranked list of all the species which
are among the fíve most common species
in each sample. There are several ways to
look at which species are the most com-
mon. In this study three different ap-
proaches are shown.
• Rated numbers: each species is rated
within each sample (from one to five)
and then the total score for each species
is calculated by adding all single value
ratings.
• Abundance: each species is ranked by
the total number of individuals in all
samples.
• In top 5: each species is ranked by how
often it has been between the five most
common species in each sample.
Table 3 shows the five most common
species for all three methods.
Feeding types
Table 4a and 4b gives information on feed-
ing types, motility and mouthparts of each
species. Table 3 shows the five most com-
mon species obtained by the three de-
scribed methods. Scoloplos armiger, Me-
diomastus fragilis, Polydora ciliata are
burrowers, Chaetozone setosa, Mediomas-
tus fragilis, Polydora ciliata are surface
deposit feeders. Burrowers could also be
called “sub surface deposit feeders” and
these four species could also be described
as deposit feeders. Pholoe inornata is a
carnivore and Exogone naidina is charac-
terized as a herbivore as well as a carni-
vore. Thyasira flexuosa is a fdter feeder as
well as Polydora ciliata also sometime act
as a suspension feeder. The dominant
species therefore seems to be mainly de-
posit feeders.
Species diversity measures
Species richness is the simplest measure of
biodiversity and is simply a count of the
number of different species in a given area.
Species richness can with caution be used,
along with other factors, as a measure for
Feeding Type Rated numbers % Abundance % In top 5 %
Scoloplos armiger S 1 16.0 2 8.3 1 14.3
Chaetozone setosa S 2 10.5 3 8.1 3 7.3
Mediomastus fragilis S 3 10.4 1 10.2 2 7.9
Pholoe inornata C 4 4.4 10 2.8 4 4.4
Ahra nitida s 4 4.7 9 3.3 6 3.8
Thyasira flexuosa F 5 4.6 8 3.9 5 4.4
Polydora ciliata S 16 1.5 4 6.6 21 1.3
Exogone naidina H/C 11 1.9 5 5.1 15 1.9
Table 3. Top five species from the three methods of frequency evaluation, ranked, abundance and “in top 5”.
The species are numbered for each method and percentages are also show. H: Herbivore. C: Carnivore. F:
Filter-fecding S: Surface deposit feeding.