The Transfer of Harmful Aquatic Organisms and Pathogens with Ballast Water and Their Impacts - Global Maritime Transport and Ballast Water Management: Issues and Solutions - page 45

Not all introduced species are considered harmful, in some cases this is quite the
reverse, as some provide for important industries providing employment and the
sustained production of valued products. Examples include the many clam species,
oysters and shrimp that have been cultivated. However, some may become so
prolifi c to create some unwanted effects, such as the recent expansion and fouling
of the Pacifi c oyster in the North Sea following increased recruitment, arising from
changes in climate (Reid and Valdés 2011 ). However a latent threat to the environ-
ment, human health, property or resources remains as a non-impacting species may
turn into an invasive species at a later stage.
Great harm can be caused by the introduction of one harmful species. For
instance, the Chinese mitten crab Eriocheir sinensis has resulted in economic dam-
age to pond fi sheries and damage to river banks from burrowing with the resultant
accumulations leading to increased dredging costs (e.g. Gollasch 1999 ). The zebra
mussel Dreissena polymorpha , originally from the Black Sea region, has expanded
its range in Europe and now is extensively distributed in North America. It has
resulted in environmental changes to lakes and rivers; but, on account of its ability
to attach to surfaces with byssal threads, has fouled abstraction piping and thrash
racks of power stations and municipal water supplies, and continues to do so (Hebert
et al. 1989 ; Carlton and Geller 1993 ; Johnson and Padilla 1996 ; van der Velde et al.
2010 ). The predatory sea star Asterias amurensis arrived to Australia from the
north-west Pacifi c and has caused signifi cant changes to bottom dwelling communi-
ties, some of economic importance (Buttermore et al. 1994 ; Byrne and Morrice
1997 ; Rossa et al. 2003 ). A further predator, the comb-jelly Mnemiopsis leidyi ,
was inadvertently introduced to the Black Sea from the eastern coast of the Americas.
Its vast numbers resulted in heavy predation on zooplankton, including the larval
stages of commercially important fi shes (GESAMP 1997 ; Vinogradov et al. 2005 ).
Although as a result of a further comb-jelly introduction that fed on M. leidyi its
abundance declined in the Black Sea it appeared in the Caspain Sea carried by ship-
ping using the interconnecting Volga-Don-Canal (Ivanov et al. 2000 ). It has since
appeared in the Kiel Bight and has spread to several Baltic countries and to the
southern North Sea (Javidpour et al. 2006 ) and it also expanded southwards to the
Eastern Mediterranean. The North Sea invasion was overlooked for some time as
the species was initially misidentifi ed as a native comb-jelly (Faasse and Bayha
2006 ). Using taxonomic identifi cation with microsatellites it was possible, for the
fi rst time for comb-jellies, to show that there have been two separate invasions of
M. leidyi colonizing European waters from two North American source areas. The
results show one originating from or near the Gulf of Mexico having arrived to the
Black Sea and the North and Baltic Seas population was traced to New England
populations (Reusch et al. 2010 ).
All of the summed impacts amount to a considerable economic cost which is
diffi cult to quantify. In the USA alone a comprehensive study concluded that the
estimated annual damage and/or control costs addressing introduced aquatic non-
indigenous species is $14.2 billion (Pimentel et al. 2005 ). A recent summary for
Europe that includes costs for repair, management and the mitigation of impacts