Alien hitch-hikers in the seas

Invasive species are one of the main threats to our oceans, severely affecting not only marine biodiversity but also human health and the economy. So what exactly are these mysterious creatures, where do they come from and why are they so dangerous?

Did you know?
  • An estimated 7,000 species are carried around the world in ballast water every day.
  • The comb jellyfish was introduced into the Black Sea through ship ballast water in the early 1980s and by 1994, the area’s anchovy fishery had almost disappeared.
  • The estimated cost of dealing with the freshwater zebra mussel introduction in the US for the period 1989-2000 is between US$ 750 million and US $1 billion.
  • An invasion of black striped mussels in a Northern Australian marina was discovered in time to successfully eradicate it. The operation involved using sharpshooters to protect divers from crocodiles.

Oceans are home to a large variety of species of animals, plants and microorganisms which have all evolved in isolation, separated from each other by natural barriers. But people have overcome these barriers through shipping, air travel and other means of transport, causing species to move far beyond their natural ranges and settle in new areas.

Species that have been moved - intentionally or unintentionally - into areas where they do not occur naturally are called ‘introduced species’ or ‘alien species.’ Many of them perish in their new environment but some thrive and start to take over native biodiversity and affect human lives—these are known as ‘invasive species’.

Invasive species range greatly in size. Microscopic Japanese algae have recently been found in the North Sea, while giant, one metre-long alien Pacific crabs are roaming off the Norwegian coast. Fish, crabs, mussels, clams, jellyfish, corals, seaweeds, seagrasses or marsh grasses, as well as microscopic disease-causing pathogens are just some of the introduced life-forms that have created havoc around the world.

Alien species can be transported in ship ballast water or as ‘hitch-hikers’: they can attach themselves to the hull of a ship, cling to fishing or diving gear, or travel as pathogens - carried by other organisms such as shellfish. They can also swim through artificially-created canals or be accidentally released through commercial activity such as the seafood trade. When a species establishes in a new environment, it is unlikely to be subjected to the natural controls that kept its population numbers in balance within its natural range. Without such control by predators, parasites or disease, such species tend to multiply rapidly, to the point where they can take over their new environment.

While many species that are introduced into a new environment do no harm, many others have significant ecological, economic, and human health impacts.

"For example, in the early 1990s, the Indo-Pacific lionfish was accidentally introduced into the Caribbean", says Jerker Tamelander, of IUCN’s Global Marine Programme. "With few known natural predators, the lionfish has spread rapidly and, on many reefs, reduced the number of native reef fish, crustaceans and other reef species. It is feared this may hurt commercial fisheries and further accelerate reef degradation in the region. Eradicating the lionfish is virtually impossible – it reproduces relatively quickly, has spread to many areas. It also occurs at depths that are beyond easy reach of humans".

Invasive species are a significant problem at local, regional and even global scale. Invasive seaweeds smother seabeds, invasive crabs roam the sea floor eating everything in their path, invasive jellyfish have led to the collapse of fisheries and people have been killed by pathogens carried in ballast water. European green crabs are eating their way through marine life worldwide and swarms of poisonous jellyfish are forming a ‘jellyfish belt’ off the coast of Israel.

Invasive species are extremely difficult to manage and prevention is the best – if not the only – way to address this problem. But effective prevention cannot be achieved without a high level of awareness as well as the ability to take management measures and these remain significant challenges.

"An IUCN project funded by Total Foundation was initiated in 2010 to fill critical awareness and capacity gaps", says Tamelander. "IUCN is also working with the Globallast Partnership in preparing guidance that can support ratification and implementation of the International Ballast Water Convention". Further tools IUCN has helped to develop are 'Guidelines for Development of a National Ballast Water Management Strategy', released early in 2010, and a guideline for 'Economic Assessments for Ballast Water Managemen' due for release later in 2010.
Materials are available on the IUCN Global Marine Programme Website.

For more information please contact:

Jerker Tamelander, IUCN’s Global Marine Programme

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