Marine Bioinvasions Fact Sheet: Ballast Water
What is Ballast Water?
Ballast water is fresh or saltwater held in the ballast tanks and
cargo holds of ships. It is used to provide stability and maneuverability
during a voyage when ships are not carrying cargo, not carrying
heavy enough cargo, or when more stability is required due to rough
seas. Ballast water may also be used to add weight so that a ship
sinks low enough in the water to pass under bridges and other structures.
| Ballast Water Vocabulary:
In Ballast: A ship carrying ballast water and
With Ballast: A ship with cargo and ballast water.
No Ballast On Board (NOBOB): A ship that is technically
carrying no ballast water. A NOBOB ship may be carrying
residual ballast water and sediments that could not be
pumped out of the tanks.
Ballast Exchange: The process of releasing ballast
water then taking on new ballast water.
Usually ballast water is pumped into ballast tanks when a ship
has delivered cargo to a port and is departing with less cargo or
no cargo. Ballast water is then transported and released at the
next port-of-call where the ship picks up more cargo. If a ship
is receiving or delivering cargo to a number of ports, it may release
or take on a portion of ballast water at each port. In such cases,
the shipís ballast water contains a mix of waters from multiple
Why should we be concerned about Ballast Water?
Organisms living in coastal waters may be pumped into ballast tanks
along with the water. If a ship takes on ballast water in a shallow
area, sediments and any associated organisms may be pumped into
ballast tanks. When ballast water is released, these organisms may
also be released.
The release of ballast water may introduce non-native organisms
into the port of discharge. These introduced species, or bioinvaders,
are also referred to as exotic species, alien species and nonindigenous
species. Typically, very few organisms are able to survive in new
surroundings because temperature, food, and salinity are less than
optimal; however, the few that do survive and establish a population
have the potential to cause ecological and economic harm. Populations
of bioinvaders may grow very quickly in the absence of natural predators.
In turn bioinvaders may displace native organisms by preying on
them or outcompeting native species for food and habitat space.
Economic damage may occur when a bioinvader displaces species that
are harvested for food or other goods, or when bioinvaders damage
Mnemiopsis leidyi, a comb jelly (similar to a jellyfish)
feeds on anything smaller than itself that gets stuck to the sticky
lobes near its mouth, especially zooplankton. It was probably introduced
via ballast water from New England (USA) into the Black Sea. In
its new environment, Mnemiopsis has no natural predators
and has outcompeted native species for food. As a consequence, the
once profitable anchovy fisheries in Russia and Turkey have almost
One of the most widely known invasions in the United States is
that of zebra mussels into the Great Lakes. These organisms grow
on almost any structure, forming large clumps of mussels which can
clog water intake pipes and damage or impair other structures. Periodically
these organisms need to be removed from pipes and other structures
which requires time, money, and possibly specialized equipment.
Another example is Teredo navilis, a ship worm that is
actually a bivalve (a relative of clams), that was introduced to
the United States during colonial times on wooden ships. Ship worms
are the termites of the sea, they bore holes into wood and damage
wooden docks, piers, and seawalls. This damage has prompted the
treatment of wood with chemicals that discourage Teredo from
attacking the wood, however these chemicals pollute the surrounding
water as they leach from the wood.
Not all invasions have disastrous effects. Populations of bioinvaders
may become economically profitable if they are harvested for food
or commercial goods. Other exotic species may fill in a niche that
was previously vacant in an ecosystem.
How do organisms survive in ballast tanks?
At present, we can not predict which organisms will die during
a long journey in a ballast tank or why some are still alive when
ballast water is released. Larger organisms often survive the journey
by eating smaller ones. When faced with unfavorable conditions,
some microorganisms and plankton species will form spores or other
tough outer coverings for protection. As a spore, an organism may
survive for a long time without food or in a different salinity
or temperature than its natural environment. Once the environment
becomes favorable again, such as when they are discharged into a
port, the organism may change back to its active form.
Organisms may establish semipermanent or permanent communities
in the layer of water and sediment that often exists in the bottom
of ballast tanks. In these situations, adult organisms may reproduce
and release larvae into ballast water while adults remain in the
sediment. This pathway leads to the release of the same nonindigenous
species into multiple ports.
What can be done about this problem?
There are two basic approaches to dealing with bioinvaders: stop
them from invading in the first place, or eliminate organisms that
have invaded. Getting rid of established invaders is practically
impossible; keeping established invaders from causing damage is
very difficult and expensive. Stopping invasions before they occur
is the more practical and economical solution in the long term.
In order to stop an invasion, organisms must not be discharged
from ballast tanks. This can be achieved by not taking organisms
into ballast tanks, killing organisms during the voyage, or not
discharging organisms when ballast water is released. More research
needs to be conducted on methods to prevent introductions of unwanted
species. Unfortunately, no ballast water treatment method can completely
eliminate the risk of introducing exotic species. The goal of managing
ballast water is to minimize the risk, possibly by targeting species
that are known to have the potential to cause ecological and economic
The United States requires all ships traveling in the Great Lakes
or the Hudson River above the George Washington Bridge to exchange
ballast water in the open ocean prior to entering these waterways.
With the exception of these two waterways, no mandatory regulations
exist for minimizing the risk of exotic species introductions in
the ocean or other waterways in the United States.
The International Maritime Organization (IMO), an United Nations
organization, recommends that ships exchange ballast water in the
open ocean to minimize the risk of introducing nonindigenous organisms
to coastal waters. The organization is working on adding ballast
water regulations to the International Convention for the Prevention
of Pollution from Ships, 1973 (MARPOL) which all member countries
Because the transfer of nonindigenous species via ballast water
is an international issue, regulations for the management of ballast
water to prevent introductions will be most effective if applied
Ballast water is one of the major pathways for the introduction
of nonindigenous marine species. Because of the potential for ecological
and economic damage posed by these organisms, ballast water should
be managed to minimize the risk of species introduction.
Carlton, James T. and Bridget A. Holohan, eds. March 1998. USA
Ballast Book 1998-1999: Ballast Research in the United States of
National Research Council. 1996. Stemming the Tide: Controlling
Introductions of Nonindigenous Species by Shipsí Ballast Water.
On international environmental agenda: garbage, ballast water and
emissions. Marine Log 75(896): pp15-19. March 1995.
The Introduction of Nonindigenous Species to the Chesapeake Bay
via Ballast Water. A Chesapeake Bay Commission Report. January 5,