Fróðskaparrit - 01.01.2007, Síða 151

BOTNDÝR í BLEYTBOTNI Á FØROYSKUM FIRÐUM
149
Results
In this paper we analyzed the species com-
position of sixty three 0.1 m2 grab samples
including a total of 285 species and 17254
individuals.
Species richness and abundance
The average number of species per 0.1 m2
was 29 and minimum and maximum spe-
cies numbers are 5 and 66 respectively.
The average number of individuals per 0.1
m2 was 236 and varies between 8 and
1655.
When compared with different sedi-
ment types there is no clear difference in
species number or abundance (Table 1).
Compared with depth there seems to be
fewer species and slightly fewer individu-
als in depths from < 20 meters than the
other two depth groups. In the group <20
m there are 23 species in average com-
pared to 33 and 32, and 194 individuals in
average compared to 267 and 217. The
species number and abundance for sedi-
ments with low ignition loss (<30 mg/kg)
are rnuch lower than the other two groups
with higher amounts of organic matter in
the sediment.
Table 2 shows the percentage of species
and individuals for the major taxonomic
groups in relation to type of sediment,
depth and ignition loss. The general picture
shows a clear dominance of polychaetes
both in species richness and abundance
followed by mollusks, crustaceans, echino-
derms and other groups. 67% of all the
species are polychaetes and 79% of all the
individuals are polychaetes.
Number two are the mollusks with 17%
in species richness and 14% in abundance
and then comes the crustaceans, echino-
denns and others with less than 6% each.
If species richness and abundance are
compared with sediment type, depth and
content of organic material in the sediment
(loss by ignition) all groups are fairly con-
stant except the crustaceans. In sandy sedi-
ments on average 14% of the total number
of species are crustaceans compared to 2%
in mixed sediments and 3% in silt/clay
sediments. The same tendency is observed
in abundance. In average there are more
species of crustaceans above 20 meters
compared to the two deeper depth inter-
vals. On average 11% af all species are
found above 20 meters compared to 3%
and 2% respectively for the deeper groups.
The same tendency can be seen in abun-
dance but not so clear. With regard to or-
ganic content in the sediment it is very
clear that the highest numbers of crus-
tacean species are found in sediments with
low organic content. Twenty one percent of
thc crustacean species are found in the less
than 30 mg/kg group compared to 4 and
2% in the two groups with higher ignition
loss.
Species composition
In the present paper we investigated sixty
three grab samples (0.1 m2) and identified
285 different species, 170 (59.6%) species
of polychaetes, 53 (18.6%) species of mol-
lusks, 29 (10.2%) species of crustaceans,
16 (5.6%) species of echinoderms, 4
(1.4%) species of cnidarians, 2 (0.7%)
species of nemerteans, 1 (0.4%) species of
priapulids, 2 (0.7%) species of phoronids,