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 42

Table 2 Summary of numbers of different orga nisms per litre

Numbers and range Mean SD

No. tanks sampled per litre per litre

Zooplankton 429 0-172 4.64 ± 0.71

Phytoplankton 273 1-49.7 × 10 6 299 × 10 3 ± 183 × 10 3

Bacteria 11 2.4 × 10 8 −1.9 × 10 9 8.3 × 10 8 ± 1.7 × 10 7

Viruses 7 0.6 × 10 9 −14.9 × 10 9 7.4 × 10 9 ± 2.9 × 10 9

From Gollasch and McCollin ( 2003 ) and IMO ( 2003 )

There is not only a high diversity of species in transit with ships, but also large
numbers of individuals that may be transported and that might survive to a destina-
tion port region. The overall numbers of organisms recorded from ballast water have
been reported by the ICES/IOC/IMO Study Group on Ballast and Other Ships
Vectors (SGBOSV) under the four headings: virus-like particles, bacteria, phyto-
plankton and zooplankton (see Table 2 ). The purpose was to provide guidance for
the development of ballast water discharge standards for the BWM Convention.
Any estimates of the numbers of the different groups to be in transit are likely to be
underestimates because species that reside within sediments, and those planktonic
species that pass through the plankton nets, using the standard mesh sizes 55 and
80 m, during BWS, do not get considered (Gollasch and McCollin 2003 ). During

the performance test of ballast water treatment systems more than 29,000 zooplank-
ton organisms greater than or equal to 50

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m in minimum dimension per m 3 and
more than 47,000 phytoplankton cells greater than 4

ʼ

m in minimum dimension per
milliliter have been found in pumped ballast (Gollasch and David, unpublished).
Such great numbers of living organisms taken up during ballasting indicates a high
probability of a viable population evolving following discharge in new environ-
ments, often referred to as propagule pressure.

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Chain of Events for a Species Introduction

The previous section of this chapter has shown that an enormous number of species
in high organism concentrations are being transferred with ballast water. However,
only the transport of a species does not result in a colonization of a new region,
there is a chain of events that a species must endure in order to become established
within a new environment (Carlton 1986 ; Hayes 1998 ). This starts with the uptake
of ballast water. As many species have seasonal planktonic stages it is during those
periods of abundance that suffi cient surviving numbers may go on to later form a
viable inoculum at discharge. Suspended sediments can also result in cysts and
benthic biota becoming transmitted with the same ultimate capability. Having survived
the uptake process the voyage(s) must be endured followed by the trauma during
discharge. On arrival suffi cient numbers will be needed to establish a population.
The numbers required to develop new populations is generally unknown but