78
delicacy in Chinese cuisine, invaded the North Sea in the early twentieth century. It
quickly became abundant and established self-sustaining populations in German
waters disturbing fi shery and aquaculture and, among other things, increasing bank
erosion. The monetary impact caused by this invader in German waters alone was
estimated at approximately 80 million Euros from its advent locally (Gollasch
2011 ). Recently, however, particularly in the absence of fi sh, the mitten crab has
been harvested in northern Germany and sold in Europe at a price of € 5–8 per kg
(Woke 2012 ). Additionally, it is also seen as a new source of crab for the expanding
Chinese market, where the value of sold crabs was estimated as high as € 3–4.5 m
between 1994 and 2004 (Gollasch 2011 ). Thus, what at fi rst seemed to be an adverse
alien species turned out to be a new profi table ecosystem good .
Generally, it is estimated that over 120 non-native aquatic species are present in
the Baltic Sea, about 80 of which have established viable, self-reproducing populations in at least parts of the region (Battle 2009 ). However, documented data on
environmental impacts is available for only 33, and just 4 species have shown strong
impacts on native communities and ecosystem functioning (Battle 2009 ; Olenin
et al. 2010 ). For example, the invasive dinofl agellate Prorocentrum minimum
(Pavillard) Schiller was seen to potentially spread and cause signifi cant impacts on
plankton communities, habitats and ecosystem functioning (Olenin et al. 2009 ).
One of the most recent examples of bioinvasion in the Baltic Sea was the introduction of a comb jellyfi sh Mnemiopsis leidyi (Kube et al. 2007 ), one of the world’s top
100 worst IAS due to its predatory success, partly attributable to its effective foraging strategy (Colin et al. 2010 ). Nonetheless, unlike in the Black Sea, where the
introduction of this jellyfi sh led to the collapse of the whole ecosystem (Kideys
2002 ), this species does not seem to pose any direct threat to the Baltic Sea fi shery
(Jaspers et al. 2011 ). In other words, it has to be stressed that no signifi cant degradation of local ecosystems with adverse socioeconomic consequences has taken place
in the Baltic Sea as a result of IAS. For that reason, AS and IAS have received far
less attention than other stressors affecting biodiversity in the Baltic Sea. In fact,
many stakeholders consider the bioinvasion problem in the region as relatively
minor. What is, however, dangerous for the Baltic Sea ecosystem is a possible synergistic effect of multiple environmental pressures and IAS. Consequences of such
multiple pressures are unknown and may negatively affect ecosystem services and
functions.
4.3 Uncertainty in Risk Assessment
The above-mentioned dual nature of AS causes a number of disagreements among
stakeholders, as well as uncertainties that are mainly due to the lack of reliable and
conclusive scientifi c data on different aspects of invaders. The absence of information necessary for an adequate risk analysis – required for developing a regional
policy instrument of marine governance – is regarded as the main obstacle to effective risk assessment and IAS management in the Baltic Sea (Lemke et al. 2010 ;
K. Smolarz et al.
delicacy in Chinese cuisine, invaded the North Sea in the early twentieth century. It
quickly became abundant and established self-sustaining populations in German
waters disturbing fi shery and aquaculture and, among other things, increasing bank
erosion. The monetary impact caused by this invader in German waters alone was
estimated at approximately 80 million Euros from its advent locally (Gollasch
2011 ). Recently, however, particularly in the absence of fi sh, the mitten crab has
been harvested in northern Germany and sold in Europe at a price of € 5–8 per kg
(Woke 2012 ). Additionally, it is also seen as a new source of crab for the expanding
Chinese market, where the value of sold crabs was estimated as high as € 3–4.5 m
between 1994 and 2004 (Gollasch 2011 ). Thus, what at fi rst seemed to be an adverse
alien species turned out to be a new profi table ecosystem good .
Generally, it is estimated that over 120 non-native aquatic species are present in
the Baltic Sea, about 80 of which have established viable, self-reproducing populations in at least parts of the region (Battle 2009 ). However, documented data on
environmental impacts is available for only 33, and just 4 species have shown strong
impacts on native communities and ecosystem functioning (Battle 2009 ; Olenin
et al. 2010 ). For example, the invasive dinofl agellate Prorocentrum minimum
(Pavillard) Schiller was seen to potentially spread and cause signifi cant impacts on
plankton communities, habitats and ecosystem functioning (Olenin et al. 2009 ).
One of the most recent examples of bioinvasion in the Baltic Sea was the introduction of a comb jellyfi sh Mnemiopsis leidyi (Kube et al. 2007 ), one of the world’s top
100 worst IAS due to its predatory success, partly attributable to its effective foraging strategy (Colin et al. 2010 ). Nonetheless, unlike in the Black Sea, where the
introduction of this jellyfi sh led to the collapse of the whole ecosystem (Kideys
2002 ), this species does not seem to pose any direct threat to the Baltic Sea fi shery
(Jaspers et al. 2011 ). In other words, it has to be stressed that no signifi cant degradation of local ecosystems with adverse socioeconomic consequences has taken place
in the Baltic Sea as a result of IAS. For that reason, AS and IAS have received far
less attention than other stressors affecting biodiversity in the Baltic Sea. In fact,
many stakeholders consider the bioinvasion problem in the region as relatively
minor. What is, however, dangerous for the Baltic Sea ecosystem is a possible synergistic effect of multiple environmental pressures and IAS. Consequences of such
multiple pressures are unknown and may negatively affect ecosystem services and
functions.
4.3 Uncertainty in Risk Assessment
The above-mentioned dual nature of AS causes a number of disagreements among
stakeholders, as well as uncertainties that are mainly due to the lack of reliable and
conclusive scientifi c data on different aspects of invaders. The absence of information necessary for an adequate risk analysis – required for developing a regional
policy instrument of marine governance – is regarded as the main obstacle to effective risk assessment and IAS management in the Baltic Sea (Lemke et al. 2010 ;
K. Smolarz et al.