BSEP116B Biodiversity in the Baltic Sea - Helcom

tion of ice cover, either through reduced ice extent
or a shortening of the ice season, is expected to
reduce the reproductive success of these species
(ICES 2005a). As grey seals can also breed on land,
a lack of sufficient ice and snow cover is more
harmful for ringed seals. Some ringed seals have
been observed to give birth on land, but in such
cases pups are exposed to predation, hypothermia
and occasionally also to human disturbance. Therefore,
the majority of pups born on land can be
expected to die before weaning.
A lack of ice, and particularly a lack of ice-scraping
in shallow-water areas, may also cause changes
in littoral communities. Ice-scraping plays an
important role in successive plant dynamics in the
Baltic Sea, for both vascular plants and algae (e.g.,
Kiirikki 1996). Moreover, the ice cover supports a
specialized microscale food web because microbial
organisms occupy interstitial crevices and salt-water
channels within the ice (Granskog et al. 2006).
Such a unique microbial system would be drastically
reduced or potentially lost, if the current projections
for the sea-ice season will be realized.
Effects of projected increased runoff and
decreased salinity
The projected increase in riverine runoff would
result in higher loading of nutrients and sediment,
with a larger change expected in the northern
parts of the region. An increase in nutrient loading
will have an influence on phytoplankton species
composition and primary production, and may be
Flounder (Platicthys flesus)
expected to contribute to increased eutrophication.
Increased riverine sediment loads, caused
by increased river runoff, will also cause rocky
habitats to deteriorate as the hard substrata would
disappear. This would happen particularly within
and near estuaries. On the other hand, increased
organic matter in the water column will reduce
water transparency and may stimulate the growth
of bacteria, resulting in a food web more based on
heterotrophy, with reduced productivity at higher
trophic levels as a consequence (Berglund 2007).
Impacts on the ecosystem level are clearly difficult
to predict at present.
According to regional climate and Baltic Sea model
projections, a possible scenario for the second
half of the 21st century is a decrease in surface
water salinity in the Baltic Sea owing to increased
precipitation, and a smaller outflow of less saline
water through the Danish Straits. This would lead to
stronger stratification of the water column and a displacement
of the halocline to greater depths, with a
possible reduced mixing of the deeper water layers
and a higher probability of oxygen depletion in deep
basins. Deepening of the halocline would result in a
larger area of oxygenated sediments, increasing the
area available for colonization of macrofauna above
the halocline (Dippner et al. 2008).
Species that are clearly limited by salinity may
become important indicators for assessing the
impacts of climate change. Although it is too early
to predict the changes at the species level, the first
candidates to be impacted are likely to be species
living in the northern parts of the Baltic Sea. Many
Baltic marine species meet their salinity limit in the
northern Baltic Sea and this is where freshwater
inflow is projected to increase the most. Thus,
many ecologically significant species would probably
disappear from the northern Baltic Sea, such as
bladder wrack (Fucus vesiculosus), eelgrass (Zostera
marina), blue mussel (Mytilus trossulus), flounder
(Platichthys flesus), turbot (Psetta maxima), and
many red algal species (Laine 2008).
134
In the southern parts of the Baltic Sea, there are
several algal species that require high salinities for
proliferation. In the projected low-salinity conditions,
many algae would thus be expected to disappear
from their former ranges, e.g., the brown
alga Fucus serratus, the kelp Laminaria saccharina,
various crustose red algae (e.g., Lithothamnion gla-