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The Problem

The introduction of invasive marine species into new environments by ships’ ballast water, attached to ships’ hulls and via other vectors has been identified as one of the four greatest threats to the world’s oceans and to biodiversity globally. The other three are land-based sources of marine pollution, overexploitation of living marine resources and physical alteration/destruction of marine habitat.

Shipping moves over 80% of the world’s commodities and transfers approximately 3 to 5 billion tonnes of ballast water internationally each year. A similar volume may also be transferred domestically within countries and regions each year. Ballast water is absolutely essential to the safe and efficient operation of modern shipping, providing balance and stability to un-laden ships. However, it may also pose a serious ecological, economic and health threat.

Tanker

What is ballast water?

Ballast is any material used to weight and/or balance an object. One example is the sandbags carried on conventional hot-air balloons, which can be discarded to lighten the balloon’s load, allowing it to ascend. Ballast water is therefore water carried by ships to ensure stability, trim and structural integrity.

Ships have carried solid ballast, in the form of rocks, sand or metal, for thousands of years. Since modern times, ships have used water as ballast.

It is much easier to load on and off a ship, and is therefore more efficient and economical than solid ballast. When a ship is empty of cargo, it fills with ballast water. When it loads cargo, the ballast water is discharged.
  

Cross section of ships showing ballast tanks and ballast water cycle
diagram showing loading of ballast water

diagram showing discharge of ballast water 

 

 

Ballast tank arrangements on board different types of vessels are to meet the requirement of ballast water on board. The figures below give the structural arrangements and ballast capacities on different classes of vessels.

Ballast Tank Arrangements for different types of ships
Cross section of an ore carrier Cross section of gas carrier
Cross section of an ore carrier
Cross section of a gas carrier
Cross section of a container ship Cross section of double-hull oil tanker
Cross section of a container ship
Cross section of double hull oil tanker
 
Ballast water capacities for different types of ships
VESSEL TYPE
DWT
BALLAST CONDITION
NORMAL
(tonnes)
% of DWT
HEAVY
(tonnes)
% of DWT
 

Bulk carrier
250,000
75,000
30
113,000
45
Bulk carrier
150,000
45,000
30
67,000
45
Bulk carrier
70,000
25,000
36
40,000
57
Bulk carrier
35,000
10,000
30
17,000
49
   
Tanker
100,000
40,000
40
45,000
45
Tanker
40,000
12,000
30
15,000
38
   
Container
40,000
12,000
30
15,000
38
Container
15,000
5,000
30
n/a
   
General cargo
17,000
6,000
35
n/a
General cargo
8,000
3,000
38
n/a
   
Passenger/RORO
3,000
1,000
33
n/a
   

The distribution of ballast within a vessel will depend on the design criteria, size and strength of the vessel.

Source: Australian Quarantine & Inspection Service 1993. Ballast Water Management. Ballast Water Research Series Report No. 4 AGPS Canberra.

Ballast needs Vessel types Typical pumping rates (m3/h)

Ballast replaces cargo

Ballast required in large quantities, primarily for return voyage.

Dry bulk carriers

Ore carriers

Tankers

Liquefied-gas carriers

Oil bulk ore carriers

5,000–10,000

10,000

5,000–20,000

5,000–10,000

10,000–15,000

Ballast for vessel control

Ballast required in almost all loading conditions to control stability, trim, and heel.

Container ships

Ferries

General cargo vessels

Passenger vessels

Roll-on, roll-off vessels

Fishing vessels

Fish factory vessels

Military vessels

1,000–2,000

200–500

1,000–2,000

200–500

1,000–2,000

50

500

50–100

Ballast for loading and unloading operations

Ballast taken on locally in large volumes and discharged in same location.

Float-on, float-off vessels

Heavy lift vessels

Military amphibious assault vessels

Barge-carrying cargo vessels

10,000–15,000

5,000

5,000

1,000–2,000

a The three categories of ballast needs are not mutually exclusive. For example, a vessel in which ballast replaces cargo may also require ballast to control stability.
 
A potentially serious environmental problem arises when this ballast water contains marine life.

There are thousands of marine species that may be carried in ships’ ballast water; basically anything that is small enough to pass through a ships’ ballast water intake ports and pumps.

These include bacteria and other microbes, small invertebrates and the eggs, cysts and larvae of various species. 

The problem is compounded by the fact that virtually all marine species have life cycles that include a planktonic stage or stages. 

Even species in which the adults are unlikely to be taken on in ballast water, for example because they are too large or live attached to the seabed, may be transferred in ballast during their planktonic phase.

Clam life cycle
Clam life cycle

 Diagram of the Prawn life cycle
Prawn life cycle

 

Over the past millennia, marine species have dispersed throughout the oceans by natural means, carried on currents and attached to floating logs and debris.

Natural barriers, such as temperature and land masses, have prevented many species from dispersing into certain areas. This has resulted in the natural patterns of biogeography observed in the oceans today. 

In particular, the pan-global tropical zone has separated the northern and southern temperate and cold water zones. This has allowed many species to evolve quite independently in these latter zones, resulting in quite different marine biodiversity between the north and the south. 

In tropical areas species have not faced the same barriers. This is exemplified by the relatively homogenous marine biodiversity spanning the huge area of the Indo-Pacific, from the east coast of Africa to the west coast of South America. 

An example of marine biogeography/biodiversity contours.
Image showing Species Diversity


Humans have of course aided this process for as long as they have sailed, mainly by dispersing marine species that have attached to the hulls of vessels. The commencement of the use water as ballast, and the development of larger, faster ships completing their voyages in ever shorter times, combined with rapidly increasing world trade, means that the natural barriers to the dispersal of species across the oceans are being reduced. In particular, ships provide a way for temperate marine species to pierce the tropical zones, and some of the most spectacular introductions have involved northern temperate species invading southern temperate waters, and vice versa.

It is estimated that at least 7,000 different species are being carried in ships’ ballast tanks around the world. The vast majority of marine species carried in ballast water do not survive the journey, as the ballasting and deballasting cycle and the environment inside ballast tanks can be quite hostile to organism survival. Even for those that do survive a voyage and are discharged, the chances of surviving in the new environmental conditions, including predation by and/or competition from native species, are further reduced. However, when all factors are favourable, an introduced species by survive to establish a reproductive population in the host environment, it may even become invasive, out-competing native species and multiplying into pest proportions.

As a result, whole ecosystems are being changed. In the USA, the European Zebra Mussel Dreissena polymorpha has infested over 40% of internal waterways and may have required between US$750 million and US$1 billion in expenditure on control measures between 1989 and 2000. In southern Australia, the Asian kelp Undaria pinnatifida is invading new areas rapidly, displacing the native seabed communities. In the Black Sea, the filter-feeding North American jellyfish Mnemiopsis leidyi has on occasion reached densities of 1kg of biomass per m2. It has depleted native plankton stocks to such an extent that it has contributed to the collapse of entire Black Sea commercial fisheries. In several countries, introduced, microscopic, ‘red-tide’ algae (toxic dinoflagellates) have been absorbed by filter-feeding shellfish, such as oysters. When eaten by humans, these contaminated shellfish can cause paralysis and even death. The list goes on, hundreds of examples of major ecological, economic and human health impacts across the globe. It is even feared that diseases such as cholera might be able to be transported in ballast water. 

EXAMPLE

* Comb jelly (Mnemiopsis leidyi)

Comb jellyThe comb jelly, Mnemiopsis leidyi, is endemic to temperate to subtropical estuaries along the North and South American Atlantic coast. It was first recorded in the Black Sea in 1982, where it became well established, occurring in massive numbers. It also spread rapidly to the Azov, Marmara and Eastern Mediterranean, and towards the end of 1999, was recorded in the Caspian Sea, where its biomass eventually exceeded levels ever recorded in the Black Sea.
Mnemiopsis feeds on the same zooplankton as many of the commercial fish species in the area, and had a devastating impact of the fisheries. Landings of anchovy, for example, dropped to one-third of their previous levels, causing losses of around $ 500 million per year. Similar reductions in the biomass of kilka were experienced in the Caspian.
The decrease in zooplankton caused by Mnemiopsis also had impacts on the food web, causing an increase in phytoplankton, and a decline in predatory fish species and seals.
More recently, the accidental introduction into the Black Sea of another comb jelly – Beroe cf ovata – which is a predator of Mnemiopsis, has resulted in a major decline of Mnemiopsis there, and a substantial recovery of the ecosystem.

  • Photo: CSIRO   Sources: GloBallast 2002, Shiganova et al, 2004.


There are hundreds of other examples of catastrophic introductions around the world, causing severe human health, economic and/or ecological impacts in their host environments.

Invasive marine species are one of the four greatest threats to the world’s oceans! Unlike other forms of marine pollution, such as oil spills, where ameliorative action can be taken and from which the environment will eventually recover, the impacts of invasive marine species are most often irreversible!

 

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