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 38

There will have been many further transmissions during the periods of colonisation
and wrecks of vessels may have seeded species in new regions. The more modern
forms of transit will have dispensed organisms with solid ballast and utilised water
in its place. With this, all ships had, and have, the capacity of spreading species
unintentionally (e.g., with ships fouling or ballast, associated with the cargo of ves-
sels or transported on deck) (e.g., Gollasch et al. 2002b; Fofonoff et al. 2003 ;
Minchin et al. 2006 , 2009 ; Carlton and Eldredge 2009 ).
Ships may transfer organisms over long distances (e.g., across oceans and seas),
termed a primary introduction, whereas regional transport is considered as the facil-
itator of secondary transfer. It should be noted that even short distance transfers are
of concern (e.g., Ruiz et al. 2000 ; David et al. 2007 ) in order to avoid negative
impacts of species when being moved within, e.g., one regional sea or neighbouring
waterbodies via inland canals.
In aquatic environments there are seven principal categories as to how species
are spread (pathways). Each pathway enables several ways a species may be trans-
ferred (vectors). Overall, there are more than 50 recognised vectors (ICES 2005 ;
Minchin et al. 2005 ). Shipping is considered to be the principal pathway worldwide,
by which species are spread. The prime vectors involving shipping are ballast water
and sediments accumulated at the tank bottom as well as hull fouling, where also
free-living (non-fouling) species were found (Faubel and Gollasch 1996 ; Gollasch
2002 ). Species have also been transported as fouling and free living stages in sea
chests (Coutts and Dodgshun 2007 ), as fouling inside ballast tanks, with anchor
chains and as fouling in the engine cooling water pipework as well as with cargo. In
some cases several vectors may be responsible for the transmission of a single spe-
cies (Minchin et al. 2007a , b , c ).
Ballast water also contains sediments, usually obtained in estuarine areas and
shallow turbid bays. These sediment accumulations, that can range from silt to
sands, settle on the bottom ballast tanks, providing a niche for infaunal organisms.
As a consequence ballast tanks offer three different habitats to species (1) the water
itself, (2) sediments at the tank bottom and (3) the tank walls for fouling
organisms.
Species in Ballast Water Tanks
According to expert estimates, 3,000-4,000 different species are moved each day
around the globe by ships (Carlton and Geller 1993 ; Gollasch 1996 ). More recent
estimates indicate that the number of species in transit with ships is most probably
in the range of 7,000 every day (Carlton 2001 ) and this does not take into account
the transfer of microorganisms such as bacteria and pathogens. While even the
general estimates vary greatly, the dimension of species transmission must be
regarded as being exceptionally high (often referred to as colonization pressure)
and it was concluded that each vessel has the potential to introduce a species
(Gollasch 1996 ).