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Pathways in Animal Invasions 15
and B. irregularis has been put on the list of the 100 world’s worst invaders
(ISSG 2006).
2.2.1.2 Waterways and Shipping
For several centuries, humans have connected river systems by canals and cut
land bridges to enable shorter shipping routes. Today, particularly Europe has
a well-developed waterway system (Chap. 5). These interconnections also
offer organisms unique opportunities to cross biogeographical borders by
reaching the next drainage system, sea or ocean. The connection of the
Caspian Sea and Central Asian waters to Western Europe, the Suez Canal connecting
the Red Sea (Indian Ocean) with the Mediterranean Sea (North
Atlantic), and the Panama Canal connecting the Atlantic and Pacific oceans
are well-known examples (Chap. 5). The Suez Canal enabled hundreds of
species to migrate from one sea to the other, often causing considerable ecological
damage such as strongly modifying eastern Mediterranean species
communities. This phenomenon has been studied in detail and was named
the Lessepsian migration (or invasion), in “honour” of the architect of the
canal, Ferdinand de Lesseps (Por 1978; Galil 2000; Chap. 5).
Shipping offers unique opportunities for hitchhikers and stowaways to be
transported and distributed globally:
1. with cargo: for balance and stability purposes, until the 19th century ships
used soil and stones as ballast. In combination with the soil and dirt in the
ship itself, and the possibilities which cargo and containers offer in general
for stowaways, maritime transport enabled many species to reach far-distant
coasts. Notable examples include the brown rat (Rattus norvegicus)
and the house mouse (Mus musculus), also among the 100 world’s worst
invaders (ISSG 2006) and today globally distributed.
2. as hull fouling: the planktonic larvae of many sessile species regularly colonize
the hull of ships and boats. This hull fouling of ships is characterized
by crustaceans and bivalves, and may involve more than 100 species (Gollasch
2002) which are transported on a global scale. The Ponto-Caspian
zebra mussel Dreissena polymorpha, among the 100 world’s worst
invaders, is one of the best-known examples of an alien species which has
invaded Europe and North America via canals and as hull fouling (Chaps.
5 and 15). A Dreissena population also contains several parasites, among
them, the trematode Bucephalus polymorphus which continues its development
in several cyprinid species.
3. in ballast water: according to Carlton (1999), about 80 % of the world’s
commodities is transported aboard a global ship fleet of approximately
35,000 large ships. For more than 100 years, ships have used ballast water
for stability purposes. Huge cargo vessels of over 300,000 t carry up to one
third of their volume as water when unloaded, amounting to some 12 bil-