Aquatic ecosystems tend to be fairly complex and potentially very fragile. The loss of any species may or may not have a big impact, but the introduction of a species that does not belong can be catastrophic. Aquatic nuisance species have drastic effects on the ecosystems into which they are introduced. Each year, thousands of such species create untold problems for local aquatic ecosystems.
Definition of an aquatic nuisance species
An aquatic nuisance species refers to any species that is not native to a body of water and that causes excessive damage to it. The damage may be due to consumption of natural resources, rapid reproduction rate, the spread of diseases or destruction of the natural predators in a given area. An aquatic nuisance species may be a plant, fish, invertebrate or other aquatic animal, or it may be such things a bacteria or virus.
Aquatic nuisance species sources
Nearly all common sources for the introduction of aquatic nuisance species are human-derived. Ocean-going vessels may bring species from thousands of miles away in their ballast water, the bilge or on the underside of the vessel. Fishermen or recreational boaters might carry organisms from one lake or stream to another by improperly cleaning equipment that comes into contact with the water.
The most preventable and potentially most damaging sources of aquatic nuisance species are plants that are raised for aquatic landscaping and unwanted pets that are released. Many beginning aquarists purchase fish without knowing the adult size they will reach and without being aware of their lifetime care requirements. When the fish outgrow the tank, they are dumped in a local body of water due to ignorance or disregard for non-native species laws.
Examples of aquatic nuisance species
Zebra mussels are a huge issue in the Northeastern United States, where they were introduced to local waters by international shipping vessels. The mussels reproduce rapidly, interfering with such things as water treatment facilities.
In Florida, the softball-sized apple snail Pomacea canaliculata, which was very popular among aquarium hobbyists, caused immense damage to the local ecosystem. Not only are they voracious eaters of aquatic vegetation, but they breathe air off the surface of the water and lay their eggs above water, so they have also done a lot of damage to terrestrial plants.
Common goldfish are inexpensive and readily available, and many people see them as a child's pet. Few realize that they often reach sizes in excess of 18" and can live 30 years or more. These fish are also extremely hardy and adaptable to a wide variety of conditions, so there are few bodies of water where they can't survive. They are territorial and eat a wide variety of plants, bugs, small fish and the eggs of other fish species.
Impact of an aquatic nuisance species
The control and/or eradication of aquatic nuisance species in the United States alone costs billions of dollars every year. Recent statistics state the number at about $137 billion. In some cases, the invasive species can completely sterilize a closed system such as a lake or pond. Non-native plants often act as weeds and choke out native plant species. Nuisance species may include floating plants that block sunlight to the organisms underneath or very large plants that can fill the water and make it useless for fishing or recreation. Some instances of nuisance species, such as freed domestic goldfish, have required systematic poisoning of entire lakes in order to get the population under control.