Nonindigenous Species and the Marine Environment

In 1958, the eminent scientist Charles Elton wrote of the threats posed by nonindigenous species. His warnings went largely ignored - and their effects are now considered by environmental scientists as one of the most significant components of human-mediated global change.

A study recently published in the journal BioScience estimated that approximately 50,000 nonindigenous species - also termed non-native, exotic or alien species - have been introduced, accidentally and purposefully, into the United States. While some, such as food crops, are considered as beneficial, others have clearly had a detrimental impact. Introduced pathogens threaten public health and a variety of invaders have caused widespread environmental damage. According to the report in BioScience nonindigenous species may be responsible for economic losses in the U.S. totalling an estimated $137 billion each year. They have reduced and continue to threaten native biodiversity and have diminished the aesthetic quality of many of the nation's unique environments.

The Problem

• Studies on the distribution and effects of nonindigenous species have focused primarily on islands or on mainland terrestrial and freshwater environments. Nonetheless, their impacts on marine environments and associated fauna and flora can be serious. For example:
  • The ballast water-mediated invasion of the Black and Azov Seas by the voracious zooplankton predator Mnemiopsis leidyi (a comb jelly) was implicated in a sharp decline in fisheries productivity.
  • San Francisco Bay is considered to be significantly and permanently altered as a result of the introduction of over 230 nonindigenous marine and brackish water species.
  • A variety of mammals, particularly cats and rats, have eliminated or vastly reduced colonies of seabirds from islands around the world, and have contributed to the extinction or near- extinction of various species such as the Jamaica petrel, Bermuda petrel and Zino's petrel.
  • Epizootic ulcerative syndrome, a disease affecting freshwater and estuarine fishes, has spread across southeast Asia and the Indian subcontinent over the last three decades; the cross-border trade in aquaculture products and ornamental fish is considered to be the cause of its geographic expansion.
• Human health may also increasingly be at risk. A study published in the science journal Nature (2000) noted high concentrations of viruses and bacteria - including the bacteria causing human epidemic cholera - in water and plankton samples in the ballast of ships entering Chesapeake Bay. Virtually no research, however, has been conducted into the potential public health and environmental impacts of the large-scale movement and transfer of micro- organisms via shipping.

The Causes

• Humans have been introducing exotic species for many hundreds of years, both deliberately and unintentionally. The growth of trade resulted in the dispersal of organisms attached to, or bored into, the hulls of ships - or, in the case of rats, carried on board the vessels themselves.
• While ship hull fouling may still be an important vector, most non-native marine species are introduced via ships' ballast water. According to the United Nation's International Maritime Organization (IMO) some 10 billion metric tons of ballast water - needed to provide balance and stability for safe ship operation - are moved around the world each year. An estimated 79 million metric tons from overseas shipping are discharged yearly into U.S. coastal waters.
• Many types of marine life can be taken on in ballast water - including bacteria, phytoplankton, small invertebrates, and the eggs and and larvae of various species, including fish. In one recent series of studies, 367 different plants and animals were found in the ballast of 159 ships arriving in Oregon from Japan. It has been estimated that, on any one day, some 3,000 species are in motion around the world in ballast water. While few organisms often survive the extreme conditions of transport, and fewer still after discharge into the recipient region, the sheer volume of water and number of organisms being transferred has ultimately facilitated hundreds of 'successful' marine invasions.
• Escapes, and deliberate releases, due to aquaculture are a continuing cause of introductions. Along the mid-Atlantic U.S. coast, for example, extensive mortalities of the eastern oyster from MSX disease since the late 1950s has been attributed to the aquaculture-mediated dispersal of the Pacific oyster and a parasite originating in Japan. Recent massive mortalities of pilchard (a commercial fish species) in Australian waters due to a herpes-virus appears to have been the result of using infected South American pilchard to feed sea-caged tuna; a 1995 epizootic killed pilchard along some 3,000 miles of coastline and, in 1998/99, an estimated 60-70% of all pilchard around western Australia perished.
• It has been suggested that even marine wildlife from such remote areas as Antarctica may be vulnerable to introductions. A recent study noted that some colonies of emperor and Adélie penguins had been exposed to infectious bursal disease virus - the cause of a serious disease notably associated with domestic chickens - and has led to speculation that it may have been introduced by the disposal of poultry products from human polar activity.
• Other mechanisms and sources of marine introductions and distribution include: the import of live bait; canals and connecting waterways (e.g., the Suez and Panama Canals); biological control programs (i.e., the deliberate release of non-native predators to control nonindigenous pest species); releases and escapes from laboratories and aquaria; and recreational boating. Genetically-modified organisms for aquaculture use (e.g., salmon) may pose a problem in the near future.

The Context

• The spread of nonindigenous species over the last century is unprecedented and far surpasses the speed and scale of natural invasions. Controlling or eradicating non-native marine species after they have successfully colonized is, in most cases, considered impossible. Predicting potential future invaders and impacts remains extremely difficult, and even the best prevention efforts cannot stop all introductions. Nonetheless, prevention programs are widely considered the best strategy in reducing the numbers of future invasions.
• An international diplomatic meeting on ballast water - under the auspices of IMO - is currently scheduled for 2003. It is hoped that a binding legal instrument addressing such concerns as performance standards for ballast water treatment and management can be agreed upon by IMO member countries. Some countries have already begun developing regulations for their territorial waters, and new ballast water treatment technologies (e.g., filtration, ozone injection, ultraviolet radiation, and chemical treatment) are being developed and evaluated.
• In response to the rapidly growing problems associated with invading species, President Clinton issued an Executive Order (13112) in February of 1999 establishing the National Invasive Species Council. The Council, which is to provide national leadership on preventing the introduction and spread of invasive species, issued a management plan (Meeting the Invasive Species Challenge) in January of 2001. In the plan the Council acknowledged the enormity of the issues surrounding nonindigenous species and noted that successful national efforts will require support and action at local, State, tribal, regional, and international levels. It also noted that "without significant additional and sustained resources for existing and new programs, it will not be possible to accomplish the goals of the Plan within the specified timeframes."

Further Reading

Barnes, D.K.A.  Invasions by marine life on plastic debris.  Nature 416(6883): 808-809, 2002.

Bax, N. et al.  Marine invasive alien species: a threat to global biodiversity.  Marine Policy 27(4): 313-323, 2003.

Carlton, J.T.  2001.  Introduced Species in U.S. Coastal Waters: Environmental Impacts and Management Priorities.  Pew Oceans Commission, Arlington, VA.  35 pp.

Endresen, O. et al.  2004.  Challenges in global ballast water management.  Marine Pollution Bulletin 48(7-8): 615-623.

Grosholz, E.  2002.  Ecological and evolutionary consequences of coastal invasions.  Trends in Ecology and Evolution 17(1): 22-27.

Lodge, D.M. et al.  2006.  Biological invasions: Recommendations for US policy and management.  Ecological Applications 16(6): 2035-2054.

National Invasive Species Council. 2001. Management Plan: Meeting the Invasive Species Challenge.

Pimentel, D. et al.  2005.  Update on the environmental and economic costs associated with alien-invasive species in the United States.  Ecological Economics 52(3): 273-288.

Ruiz, G.M et al.  2000.  Global spread of microorganisms by ships.  Nature 408: 49-50.