BSEP116B Biodiversity in the Baltic Sea - Helcom

ciale), the red alga Delesseria sanguinea, and the
green alga Ulva lactuca.
Many littoral invertebrate species in the northern
Baltic Sea, living among macroalgae and vascular
plants or in soft bottoms, have their lowest salinity
limits close to 4–6 psu (e.g., the shrimp Crangon
crangon, the isopod Idothea baltica and the
soft-shelled clam Mya arenaria). Similarly, in the
southwestern Baltic Sea, many oceanic species may
withdraw from the Baltic side of the Danish Straits.
Such invertebrates may include, for example, the
crabs Carcinus maenas and Hyas araneus, and the
Littorina snails.
Spawning of the most important commercial fish
species in the Baltic Sea, namely cod, is dependent
on a salinity higher than 11 psu. Thus, reduced
salinity together with potentially increased hypoxia
in the Baltic Sea would diminish the volume of the
cod spawning habitat (Nielsen & Kvaavik 2007).
Because many of the above-mentioned species
are key species in the Baltic Sea ecosystem, the
cascading impacts will most likely resonate in other
species in both the marine ecosystem as well as
terrestrial coastal communities.
Secondary effects of decreased salinity are also
possible. Changes in environmental conditions
may give opportunities for non-native species to
invade the ecosystem. Moreover, marine species
living at their low-salinity tolerance limit are more
sensitive to other metabolic stresses such as
higher temperatures and hazardous substances.
Higher temperatures and/or lower salinity could
therefore affect the species’ ability to deal with
toxic substances and the different physiological
regulation processes involved in the detoxification
of hazardous substances. The bioavailability of
metals increases with decreasing salinity (Dippner
et al. 2008); hence, the tolerance and the metabolic
stress of some species may be exceeded,
with consequences that are unfavourable to the
conservation aims of Baltic Sea biodiversity.
6.10.2 Conclusions
Hydrographic changes in the Baltic Sea have
already altered the distributions and ecological
interactions of the Baltic biota, and the regional
climate model projections of anthropogenic climate
change indicate that even more pronounced
Anklamer Stadtbruch, Germany
changes can be expected during this century. As
the strongest abiotic parameter regulating the
Baltic biota is salinity, the projected decrease in
salinity is expected to change the geographic distribution
limits of many species and even exclude
native species from the Baltic Sea. Most likely, the
emerging freshwater species would replace some
of the functions of marine species, but the capability
of freshwater species to compensate for the
loss of habitat-forming marine species is difficult
to predict. By monitoring certain indicator species,
known to be sensitive to a changing hydrographic
regime, the climate-induced ecosystem effects
could be better understood, assessed, and, hopefully,
predicted.
The changing climate is expected to put considerable
stress on the Baltic Sea ecosystem, making
it even more important to mitigate other human
pressures. Known associations between salinity,
temperature, toxic substances and the establishment
of invasive species, for example, indicate that
polluted environments that also undergo hydrographic
changes experience the highest establishment
rates of non-indigenous species. In addition,
climate change is likely to exacerbate eutrophication,
which may require enhanced efforts to
decrease nutrient loads to the Baltic Sea.
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