Marine
species are being carried around the world in ships’ ballast
water. When discharged into new environments, they
may become invasive and severely disrupt the native
ecology, impact economic activities such as fisheries
and cause disease and even death in humans.
Invasive
marine species are one of the four greatest
threats to the world’s oceans. The
other three are:
-
Land-based sources of marine pollution.
-
Over-exploitation of living marine resources.
- Physical alteration and destruction of coastal and marine
habitat.
What is Ballast Water?
Ballast is any material used to weight or balance an object. One example
is the sand-bags carried on conventional hot-air balloons. These can
be discarded to lighten the balloon’s load, allowing it to ascend.
In ships, ballast is used to maintain balance, stability and structural
integrity, especially when the ship is empty of cargo. Ships have
carried solid ballast, in the form of rocks, sand and metal, for thousands
of years. Modern ships use water as ballast.
Unwanted Stowaways
A problem may arise when ballast water taken on by a ship contains
unwanted marine organisms. These may be bacteria and other microbes,
planktonic species, small invertebrates and the spores, eggs and
larvae of larger species.
The potential for species transfer is compounded by the fact that
almost all marine species have planktonic stages in their life-cycle,
which may be small enough to pass through a ship’s ballast
water intake ports and pumps.
This means that species
with adult stages that are large or attached to the seabed, may
still be transported in ballast water.
