Jämförande undersökning av bottenfaunasamhället och bottenhabitatet vid Marsund/Bovik (NV Åland) och SÖ Kumlinge

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Publication Details

List of Authors: Heidi Herlevi
Publisher: Åbo Akademi, Forskningsrapporter från Husö biologiska station
Publication year: 2017
ISBN: 978-952-12-3644-0


In the summer of 2017 a study was conducted comparing the benthic fauna
composition and habitat between two areas in the Åland archipelago; one
in the northwestern middle archipelago (Marsund/Bovik) and one in the
eastern outer archipelago (Kumlinge). In total 20 stations (10 in each
area) in the coastal zone were sampled for benthic fauna in four depth
zones (0-3 m, 3-6 m, 6-10 m and >10 m). In addition, 44 and 45
stations (in Marsund/Bovik and Kumlinge, respectively) distributed among
the same depth zones were studied for vegetation and habitat by using a
drop-video method.

The species composition of benthic fauna showed no clear
differences, but rather followed the same pattern regarding dominance of
the Baltic clam (Macoma balthica) and deposit-feeding gastropods in the
genus Hydrobia. The prevalence of other species, namely the
non-indigenous polychaetes Marenzelleria spp. and some crustacean (e.g.
Ostracods) also increased with depth in both areas. The Baltic clam also
constituted the majority of the benthic biomass in both areas. However,
even other bivalves made up a significant portion of the biomass in
Kumlinge. The length distribution of M. balthica showed a dominance of
small length classes (<10 mm) and a lack of larger length classes
(>10 mm) in Marsund/Bovik, which indicates a low survival of older
individuals, especially in the shallow areas. In Kumlinge, the length
distribution was more even and shifted towards larger individuals,
although small individuals were abundant. This indicates both good
reproductive output and lower predation pressure on larger individuals
compared to Marsund/Bovik. The largest differences were caused by the
overall abundance and biomass of benthos, both of which were
substantially higher in Kumlinge.

Moreover, the diversity of habitats was also higher in Kumlinge;
both regarding average number of species per habitat and type of
habitats. There were also clear differences in the vegetation
assemblages in these two areas, as the most frequently observed species
in Kumlinge was the phaeophyte Chorda filum, whereas angiosperms
(Potamogeton spp., Stuckenia pectinata and Myriophyllum spp.) were most
abundant in Marsund/Bovik. The charophyte Tolypella nidifica was also
observed frequently in Kumlinge. Bare bottoms were abundant in both
areas, but constituted the majority of habitats only in Marsund/Bovik,
whereas mixed-vegetation habitats were most abundant in Kumlinge. Soft
bottom was the dominating sediment type in both areas. In both areas,
approximately 20 % of the sites were classified as valuable habitat.
However, habitats with high value for fish reproduction were more
abundant in Kumlinge, mostly as a result of the higher vegetation cover
in general.

Although the benthic communities in both areas seemed to be in good
condition based on the prevalence of long-lived species (M. balthica),
and a smaller proportion of opportunistic species, such as chironomids
and oligochaetes, signs of eutrophication could be discerned. In
Marsund/Bovik especially, oxygen depleted areas with hydrogen sulphide
production were frequent. Some locations were also completely covered in
mat-forming cyanobacteria. Moreover, filamentous ephemeral algae were
abundant in both areas. Habitats dominated by the perennial brown algae
Fucus vesiculosus, were scarce in both areas.

Last updated on 2020-28-01 at 08:10