The Biodiversity Institute of Ontario (BIO) is an interdisciplinary research institute dedicated to improving the understanding of biodiversity at all scales, from the genetic to the macroecological.
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Introduction
Historically, human actions have been inconsequential on the forces of nature, however, humans are now influencing the processes of the planet. The water bodies of Canada and the world are being invaded by non-native or exotic species. An exotic species is any species intentionally or accidentally transported and released by man into an environment outside its present range. These plant and animal species are considered to be among the most severe agents of habitat alteration and degradation, and they are a major cause of the continuing loss of biological diversity throughout the world.
Not all aquatic species that are introduced into new environments are successful; in fact, ecologists predict that most will fail and those that manage to survive will fail to establish reproducing colonies. An ecosystem’s resistance to exotic species depends on competition between them and native species for food and habitat. The greater the diversity in an ecosystem, the more competitors an exotic species will encounter, thereby decreasing its chances of becoming established.
How Do These Species Get Introduced?
Humans have played an important role in the introduction of non-indigenous organisms into new parts of the world as the rate of dispersal of living organisms has accelerated in proportion with increased human activity around the world. Invading species can be introduced into a new ecosystem by a variety of methods.
Unintentional Release
Many species are released into new environments without the intention of creating established populations. The release of aquarium pets into the wild is common, although it is not generally the intent of the owners to establish self-sustaining populations. Common species released from aquariums are red piranha (Pygocentrus naltereri) and convict cichlids (Cichlsoma nigofasciatum).
The accidental escape of many cultivated plants from ornamental gardens is a common mechanism for the introduction of aquatic plants. Purple loosestrife (Lythrum salicaria) which now dominates many wetlands in Canada was introduced in this way.
|Fishermen dump unused bait into the water in which they are fishing, even though their bait did not come from the same water; a significant example of this is the rusty crayfish (Orconectes rusticus). Many times pathogens are released with stocked fish, or plankton are introduced in fish transport water during fish stocking programs. Other unintentional releases include the introduction of marine algae into brackish habitats from the household disposal of seafood packaging and shells (for example, the green crab (Carcinus maenas)).
Shipping Activities
Many species are released into new environments by shipping activities. Since 1959 almost 1/3 of the exotic species in the Great Lakes have been introduced as a result of shipping activities, coinciding with the opening of the St. Lawrence Seaway.
Ocean going vessels are likely the largest vectors of biological invasion. Ships take on ballast water for stability during an ocean crossing and then dump the water before they take on cargo. More than 1 million litres of water are can be discharged by a single vessel. Biological invasions occur when ships discharge ballast water that has been taken from foreign ports. If the introduced aquatic plant or animal species is compatible with the ecological conditions of the lakes, they survive, reproduce, and disperse through the environment. This invasion mechanism has become more significant, as transoceanic crossing times have decreased. The spiny water flea (Bythotrephes cedarstroemi), and the round goby (Neogobius melanostomus) are examples of ballast water introductions into the Great Lakes.
Canals
As early as the late 1700s, canals were constructed in Northeastern North America. These canals join adjacent watersheds, allowing organisms to cross natural barriers, such as Niagara Falls. The sea lamprey (Petromyzon marinus) is a predacious, eel-like fish native to the coastal regions of the Atlantic Ocean. They were first discovered in Lake Ontario in 1830, through the Erie canal (opened in 1825) from their native habitat in the Atlantic drainage basin, they entered the rest of the Great Lakes through the Welland Canal, after it was opened in 1921. They contributed greatly to the decline of whitefish and lake trout populations in the Great Lakes.
Intentional Release
Many exotic species have been intentionally released into new water bodies. The most common example of this is fish stocking. Deliberate stocking of fish species began in the Great Lakes in the early 1870s, in order to increase the value of the fisheries. Rainbow trout and chinook salmon are two examples of fishes that were intentionally introduced to the Great Lakes.
Animal Vectors
Of all animal vectors, birds are the most important dispersal agent. Organisms can be dispersed by birds in three ways. Organisms, larvae, or eggs may be attached externally to the bird’s plumage or transported within algae wrapped around to the birds feet, legs or head. Internally, live organisms may be defecated or regurgitated from a birds stomach, and released into the environment. Thirdly, organisms may be carried directly; for example, a piscivorous bird may accidentally drop a caught fish into a nearby lake.