What are Aquatic Invasive Species (AIS)?
Aquatic invasive species (AIS) (sometimes called exotic, invasive, nonindigenous or non-native) are aquatic organisms that invade ecosystems beyond their natural, historic range. Their presence may harm native ecosystems or commercial, agricultural, or recreational activities dependent on these ecosystems. They may even harm our health.
People have helped spread species around the globe for centuries either intentionally or unintentionally. Intentional introductions involve the deliberate transfer of nuisance species into a new environment. An example of this would be someone who dumps the contents of their home aquarium into a lake. Unintentional introductions occur when invasives are transferred accidentally. For instance, zebra mussels can be spread when ballast water used for ship stability is exchanged.
In fact, aquatic nuisance species can be spread many ways including ships, boats, barges, aquaculture, aquatic recreation (fishing, hunting, boating, diving, etc.), water gardening, seaplanes, connected waterways and many other pathways. Through these and other means, thousands of terrestrial and aquatic invasive species have been introduced into our country, costing us billions annually
Examples of aquatic nuisance species in the Colorado River include:
Please note that the Colorado River watershed constitutes an area of 618,000 km2. This is an area roughly the size of France and includes large areas of 7 US states (Arizona, California, Colorado, New Mexico, Nevada, Utah, and Wyoming).This is in no way an exhaustive listing of all AIS known or thought to present a threat to the Colorado River rather, just a very few known to exist in the mainstem.
Viral Pathogens
Whirling Disease (Myxobolus cerebralis)
Largemouth Bass Virus (Family: Iridoviradea)
Algae
Didymosphenia geminate (6 species currently accepted taxonomically)
Microcystis sp. Although many species are likely native, nuisance and potentially toxic blooms on many reservoirs along the Colorado River warrant their inclusion here.
Invertebrates
Quagga mussel (Dreissena bugensis)
New Zealand Mud Snail (Potamopyrgus antipodarum)
Northern Crayfish (Oronectes virilis)
Apple Snail (Family: Ampullariidae, Genus: Pomacea)
Aquatic Plants
Giant Salvinia (Salvinia molesta)
Water Hyacinth (Eichhornia crassipes)
Water Lettuce (Pista stratiotes)
Vulnerability of the Colorado River to AIS
Historically, the Colorado River had a relatively high degree of endemism. Invasions seemed to be relatively rare pre-impoundment and organisms adapted to and evolving within such a hydrologically-flashy, sediment-laden environment were left relatively undisturbed by biological invasions from elsewhere due to these extreme conditions. Geographical isolation also played a role in maintaining a relatively pristine assemblage of aquatic organisms within the Colorado River.
The post-impoundment period (1935-1963) efficiently tamed the Colorado River from above the Grand Canyon to the US/Mexico border. The constructed aquatic ecosystem that is now the Colorado River, bears little resemblance to its former wildness. Species from more temperate areas that never could have survived in an un-dammed Colorado River, now thrive. Many sport fish were purposefully introduced during the post-impoundment period effectively displacing many native “big river” fishes many of which are now threatened with extinction. Biological invasions didn’t stop with fisheries and many aquatic, semi-terrestrial, and riparian-obligate non-native species now inhabit the Colorado River Basin.
All species are not created equal. Regions of the world vary in the degree to which natural selection has been able to optimize the conversion of resources into survivability under competition. Older areas where species have evolved under intensely competitive pressures, combined with large areas of contiguous habitat, tend to have species evolve within them that become highly invasive when introduced into other areas. For example, Asia is one such area of the world with these conditions and many AIS originate from Asia. Other examples of “young” and genetically depauperate areas being vulnerable to biological invasions is the connecting of the Mediterranean and Red Seas following the construction of the Suez Canal in 1869. Prior to the completion of the Suez Canal, the Mediterranean was relatively phylogenetically depauperate and the Red Sea, a much older ecosystem, was phylogenetically diverse. Following Suez Canal completion, over nine hundred biological invasions have occurred in the Mediterranean via the Red Sea while virtually none invaded the Red Sea from the Mediterranean. Another piece of corroborating evidence exists in the United States. In 1825, the Erie Canal connected the Great Lakes to the Hudson River. Both the Hudson River and Lake Erie had roughly equal measures of phylogenetic diversity but contained many different species between them. Upon canal completion, very few species from the Hudson River were found in Lake Erie and vice versa. It appears that phylogenetic diversity, competition pressures, and time for natural selection to occur are key components in determining which areas may be sources or sinks for biological invasions to occur.
The created ecosystem that is now the Colorado River is exceptionally young from an evolutionary standpoint. In the grand scheme, 63 years since the last major dam was constructed, is the blink of a naturally-selected eye. Compared to other, far older, aquatic ecosystems, the potential for biological invasions to occur in the Colorado River is large. Predictions about how, specifically, biological assemblages will change within the created ecosystem that is now the Colorado River are difficult. One thing seems certain however; biological changes definitely will occur and biota once native to the Colorado River will continue to suffer in a created ecosystem that has little, if any, components of structure and function necessary for their survival. Many invasions and changes may be subtle and go un-noticed while others have the potential to greatly impede and interfere with the many anthropocentric uses of one of the worlds most important water sources.