Fróðskaparrit - 01.01.2007, Blaðsíða 161

BOTNDÝR í BLEYTBOTNl Á FØROYSKUM FIRÐUM
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Species composition
A general list of the most common species
could be generated from total numbers of
individuals from all samples but there is a
risk that one or very few samples could
disturb the general picture by a heavy
domination by one species (e.g. Polydora
ciliata). Another method is to rate each
species in a sample and then add all the
values for the total samples. A third and
easy method is to count how many times
any particular species has been among the
top fíve species in each sample. Table 4
shows the three frequency methods evalu-
ated. The rank frequency method showed
that the top five species contain 54.0% of
the total value. A sirnple count of individu-
als (abundance) showed that 48.3% of all
the individuals came from the five most
abundant species, and the method of count-
ing how often each species was among the
five most abundant species in each sample
(“In top 5 frequency method”) gave
45.3%. All three methods gave Scoloplos
armiger, Chaetozone setosa and Medio-
mastus fragilis as the three most frequent
species and eight species are among the
top fíve species when all three methods are
considered.
Feeding types
From Table 3 and 4 it is evident that the
most common species (Scoloplos armiger,
Mediomastus fragilis, Chaetozone setosa)
are deposit feeders. In soft sediments a ma-
jority of the species are expected to be liv-
ing as deposit feeders compared to a ten-
dency towards a shift to filter feeding in
hard substrate habitats (Levinton, 2001).
Figure 6. Skálafjørðui' with stations froni Jørgensen
(1993), Nørrevang (1990) and Sakarisson (2000)