BSEP116B Biodiversity in the Baltic Sea - Helcom

munities that formerly consisted of native species
but are, to an increasing extent, dominated by
alien invaders. As far as is known, no native species
has become extinct in the Baltic Sea owing to
the introduction of alien species, but it cannot
be guaranteed that this will be the case in the
future. Xenodiversity (structural and functional
diversity caused by non-native species) tends to
reach and even exceed native biodiversity in terms
of the number of species and life forms, especially
in coastal lagoons and river mouths. This trend
towards increasing homogeneity of flora and fauna
between, for example, the European and North
American continents is one of the most important
changes of the geography of life since the retreat
of the continental glaciers (Crosby 1972, Leppäkoski
& Olenin 2001).
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Mytilopsis leucophaeata
developed to avoid ballast water exchange until the
vessel is 200 nautical miles off the coast of North-
West Europe in waters deeper than 200 m.
Following the road map, work has also started
to develop and agree on criteria to distinguish
between routes which pose a risk for secondary
spreading and for which ballast water management
(ballast water exchange, ballast water treatment)
could reduce this risk, and those routes
where natural spreading cannot be avoided (and
for which exemption from ballast water management
could be granted). This work is also to
ensure that a unified exemption system is created
in the Baltic and to serve as a basis for risk assessments
for voyages outside the Baltic.
6.7.3 Conclusions
Alien species are a major threat to indigenous
biodiversity, leading to the restructuring of com-
Effective reduction in the number of ship-mediated
‘stowaways of the seas’ is a high-priority
goal and there are a number of onboard ballast
water treatment systems being developed. It is
obvious that no single treatment technique alone
will be able to eliminate all types of organisms. A
combination of different physical (filtering, centrifugation,
ultraviolet light and ultrasound treatment)
and chemical techniques may prove to be
the most effective means. Some basic differences
between bioinvasions (biological pollution) and
other forms of marine pollution should be kept
in mind. While chemical and physical pollution
can be reduced or stopped, living organisms tend
to reproduce and spread if they meet hospitable
environmental conditions in the water body into
which they were initially released through shipping
or other vectors. Chemicals do not spread
actively. Furthermore, chemicals tend to decrease
over time through degradation, whereas established
alien aquatic species are permanent, and
the impacts of invasive species are usually irreversible.
In the future, climate change may enhance northward
transport of species of southern origin
with distinct advantages over the native species.
In addition, future scenarios are dependent on
economic development and political decisions,
such as those related to EU transport policy (e.g.,
trends to develop inland waterways traffic, deepening
and widening of canals), and the increase
of ship traffic, for example, along the Volga-Baltic
Waterway.