Ballast water is essential for safe and efficient modern shipping operations. But ballast water also impacts serious ecological problems due to the multitude of marine species carried in ships’ ballast water. The ballast water includes bacteria, microbes, small invertebrates, eggs, cysts and larvae of various species.
The transferred species may survive to establish a reproductive population in the host environment, becoming invasive species. At the end the ballast water impacts native species that may be multiplying into pest proportions.
What is ballast water?
Ballast water is essential for the safe operation of ships. It provides stability and maneuverability during a voyage and during loading and unloading operations. Ships are designed and built to move through water carrying cargo, such as oil, grains, containers, machinery and people. If the ship is traveling without cargo, or has discharged some cargo in one port and is on route to its next port of call, ballast water may be loaded on board to achieve the required safe operating conditions. Among others this includes keeping the ship deep enough in the water to ensure efficient propeller and rudder operation.
Water has a good weight-to-volume ratio and is carried in separate tanks used just for ballast, or in empty cargo tanks. When a vessel is departing a port, water and any sediment that may be stirred up, is loaded into the ballast tanks and unloaded again when it takes on cargo at the next port. However, the process of loading and unloading untreated ballast water poses a major threat to the environment and public health as ballast water impacts the transfer of organisms between ecosystems, from one part of the world to another.
How does the ballast water impact?
When ballast water is loaded many microscopic organisms and sediments are introduced into the ships ballast tanks. Many of these organisms are able to survive in these tanks. Ballast water impacts the environment when the ballast water is discharged and the organisms are released into new environments. If suitable conditions exist in this release environment, these species will survive and reproduce and become invasive species. In some cases there is a high probability that the organism will become a dominant species, potentially resulting in:
- The extinction of native species
- Effects on local and regional biodiversity
- Effects on coastal industries that use water extraction
- Effects on public health
- Impacts on local economies based on fisheries
Ballast water impacts the biodiversity
The problem of invasive species in ships’ ballast water is largely due to the expanded trade and traffic volume over the last few decades and, since the volumes of seaborne trade continue to increase, the problem may not yet have reached its peak yet. The effects in many areas of the world have been devastating. Actually invasive aquatic species are one of the four greatest threats to the world’s oceans. Quantitative data show that the rate of bio-invasions is continuing to increase at an alarming rate and new areas are being invaded all the time.
But how exactly does the ballast water impact the biodiversity? Species from the ballast water are considered alien if they are not native to a given ecosystem. They are also referred to as non-native species. Alien species are considered to be invasive when their introduction causes, or is likely to cause, harm to the environment, the economy, or human health.
The introduction and spread of alien invasive species is a serious global threat to marine and freshwater ecosystems. New species may completely alter the local communities, drive species to extinction as well as cause economic damage as nuisance species.
Results of the ballast water impacts
New non-native species are constantly being discovered in Scandinavia. This is partly explained by the increase in trade and travel. Climate change is indeed another important factor. With generally higher temperatures, a longer growing season, and shorter, milder winters, it will become easier for alien species to establish populations in Scandinavia. These are species that could have serious impacts on ecosystems and threaten native Scandinavian species if they become established.
Examples of actual and possible effects of non-native aquatic animals which have recently been introduced to Scandinavia from shipping are shown below:
- Round Goby. The round goby poses a serious threat to the Scandinavian aquatic ecosystems, with potential impacts on commercial fishing. Since its discovery in the Baltic Sea, this bottom-dwelling fish has rapidly spread to many areas.
- Comb Jellyfish. The invasion of the Baltic Sea by a voracious comb jellyfish from North America is one of the best-documented examples of a marine alien invasive species introduced through ballast water. It eats both zooplankton, the food of commercially important fish, and the eggs and larvae of the same fish species.
- Chinese Mitten Crab. The Chinese mitten crab has been found all over the coastal Baltic Sea and also in some adjacent rivers and lakes. It outcompetes native species of crayfish for food and space, and can cause a decline in the populations of native species.
How can the ballast water impacts cause damage?
Many alien species are unable to adapt to a new environment or are harmless if they do survive, but others pose a threat to native plants and animals. They may for instance:
- Compete with native species for food and/or habitat
- Alter the habitat in which they live
- Carry diseases or parasites
- Hybridism with native species
- Increase the risk that already threatened species will become extinct, or displace native species from an area
It should be noted that ballast water has been disposed by ships in ports, harbours and coastal waters since the early 1900’s and that during this time many non-native species have been introduced. However, recognizing the possible severity of the ballast water impacts, organizations are now taken action by developing guidelines for preventing the introduction of non-native species which aim to minimise the effects.