Introduced freshwater species

"It's depressing. I go to any island and I already know the flora."

Wendy Strahn
Chief Botanist for Species Survival Commission
IUCN - World Conservation Union.

"Biological invasion is really a bigger impact than a lot of the horrible things we hear about global warming.
Many of the impacts of global warming could, in time, be reversed, but once you homogenise the biodiversity of the world, there's really no going back from that."

David Burney, Paleoecologist.

"A non-native species is any species introduced to an area where it has not occurred since any major climatic change (5000 years)".

"An alien species is any species introduced by man, but it does not become established".
(i.e. it does not establish a breeding population)
JNCC 1997. (Joint Nature Conservation Commitee)

The process of biological homogenisation has been termed McDonaldisation - the occurrence of the same species over a wide geographic area.

This process is evident in many old European colonial countries, where species were introduced for various reasons, or were transported by trade, farming etc.

This has also occured in the UK, for example with the Brown Rat and the Rabbit. The rat was introduced unintentionally by trade, on ships from Europe, the rabbit introduced by the Romans for food from Europe.

Wild boar have recently established themselves in Kent and Hampshire, they escaped from farms in the area. Their legal status is uncertain as they were native to the UK, but were all killed. The current population causes damage to crops and game birds (such as pheasants). They currently are considered as game animals, but their actual legal status is uncertain - should they be classed as an endangered species?

Big cats - there are numerous reports of large, non-native felines observed in the UK. Though there is no hard evidence, these may also be alien or introduced species.
    Natural History Museum-Beast of Bodmin
    Strange Cats-Worldwide reports of strange cats.

4 main aspects:

1. Predation: Introduced species may predate on native ones and threaten their survival.

2. Disease/Parasites: Introduced species may bring disease or parasites native species have no resistance or immunity to.

3. Competition: Introduced species may compete with native ones for habitat, food and other resources.

4. Hybridisation: Introduced species may be related closely enough to native ones to interbreed with them.

Six processes have been identified.

1. Unintentional, unassisted and natural:

These are simply just range extensions via natural dispersal mechanisms. E.g. adhesive eggs attached to water birds.

2. Unintentional, assisted by habitat modification:

Lakes, seas etc. joined by canals. This creates new pathways and gives a species the opportunity to infiltrate new habitats.

Siltation/removal of a riverbed can create new habitats and remove old ones.

3. Unintentional, associated with human activities:

Carried in ballast water, as adults, juveniles or larvae. E.g. Zebra mussel, many saltwater barnacle species.

Escapees from aquaculture. Species farmed for food, sport etc. can escape into the wild.

4. Unintentional, associated with introductions of other species:

Parasites, mutualistic partners etc.

Eggs transferred with water plants.

5. Intentional and legal:

For aquaculture: Many species, such as Signal Crayfish, Pacific Oyster.

Food: Again, many species e.g. Carp, Rainbow Trout.

Sport: Rainbow Trout, Wels Catfish

6. Intentional and illegal:

Deliberate introduction for sports e.g. Carp in the USA.

Unwanted pets e.g. Terrapins, goldfish, tropical fish.

Released by animal rights groups e.g. Mink.

Not every individual introduced to an ecosystem will survive.
Problems occur if conditions are conducive to their survival and if males and females are introduced they may breed.

Introduced species may have little ecological effect if a suitable niche is vacant e.g. Crangonyx pseudogracilis. This is a North american freshwater shrimp, introduced to UK waters around 1936. The UK has no native stillwater shrimp species, only the river shrimp Gammarus pulex . The introduced species filled a vacant niche in the habitat.

If there is no vacant niche, the introduced species may be more successful than the current species and displace them e.g. The Signal Crayfish was imported into the UK as a second crop for Trout farms. Individuals escaped into rivers and spread. They tend to out-compete the native White-clawed crayfish and displace it. They also prey on fish eggs, creating a problem in chalk streams that trout and salmon use for spawning.

Some introduced species may need higher temperatures to survive e.g. Guppies, Tilapia and Clarias catfish (all Tropical fish) were introduced when an aquatics shop closed down to a stretch of the St. Helen's canal. This stretch received a discharge of cooling water from a glassworks. The fish survived for several years, but eventually they died out. The low Winter temperature was too low for the fishes survival. Guppies were also found in the River Lea in Hackney, this received cooling water effluent. The water was also too polluted for native fish, so the guppies had no potential predators. They also survived for several years, until the power station shut down and the pollution was stopped.

Elminius modestus is an Australian barnacle species which was introduced to UK waters by fast ships coming from Australia during the Second World War. These ships moved rapidly through waters that would otherwise cause barriers to dispersal (e.g. too cold). Elminius modestus can survive and breed in UK waters. Balanus balanoides is a native barnacle species that uses the same habitats and the same food source. Both are suspension feeders, which remove material from the water column using ciliary appendages.

E. modestus sustains a higher ciliary beat at higher temperatures, so feeds more effectively than B. balanoides , but it requires a higher winter temperature than B. balanoidesto breed.
Its current distribution is therefore subject to Winter temperature limitation.

The Nile perch is a highly predatory fish introduced for economic reasons to some large African lakes. The perch are so voracious they have wiped out populations of indigenous Cichlid species in the lakes. However, their economic value is not as high as the Cichlids - typically fetching only 1/3 of the price.

1. Pumpkin-seed sunfish: Lepomis gibbosus

This is a small (average in USA is 20cm), North American predatory fish, similar to Bass and is a distant relative of the Perch. It was introduced to Europe and the UK in the 1890's. Its bright colours meant that it was desired as an aquarium fish, inevitably there were some releases into the wild. In the UK they are widespread, but only locally common. Originally found in the South-east it has also been recorded in Somerset and as far North as County Durham. It is widespread through most of continental Europe.

2. Zebra Mussel:Dreissna polymorpha

Zebra mussels are small European bivalve molluscs. They were introduced to the North American Great Lakes system, probably in ballast water taken in by freighters from European freshwater ports.
Zebra mussels have high fecundity - they reproduce rapidly and in large numbers. They have become a problem in cooling water/irrigation water intakes, they become attached to the side of the intakes and build up - it can cost thousands of dollars to remove them.
Since their original introduction they have spread rapidly through the Great Lakes System. Measures such as ballast intake/outlet screens are being implemented to reduce their spread.

3. King Carp:Cyprinus carpio

This is a domesticated carp variety, which exhibits favourable characteristics such as high growth and potentially large size. The original wild type was introduced to the UK, from Europe in the Middle Ages. This was helped by the French conquering England - there was a growth in monasteries, it was this that aided the spread of the Carp. The King Carp variety has also been introduced into the USA and Australia in the 1800's.
It is legal to stock Carp in coarse fisheries in the UK, however any introduction is illegal in Australia.
Carp are large, messy feeders, that create large amounts of waste. Their waste can cause siltation of gravel riverbeds, and they can decimate the flora of a delicate river system.
Ornamental forms of Carp are often stocked in coarse fisheries - such as Koi carp and Ghost carp.

4. Ruffe:Gymnocephalus cernua

This is a small (average 10cm long) member of the Perch family - native to Europe. They originally only occured in Eastern England, but now have an extended range in the UK. Thanks to their small size, they can be transported with other fish if selection is not careful enough. European Ruffe were accidentally introduced to the Great Lakes system of the USA, most probably from ballast water. It is an relatively insignificant species in European waters, but became a pest in the USA. The Ruffe has a catholic diet consisting of small invertebrates, fish eggs and fry.
It has been blamed for the decline in the Loch Lomond population of Powan - a rare freshwater whitefish (Coregonid). The Ruffe has several sharp defensive spines, which can protect it against predators, though another introduced species, the Zander, predates on Ruffe greatly.

5. Goldfish:Carassius auratus

The original Goldfish was native to Southeast Asia. It has a very close relative in Europe - the Crucian Carp.
Centuries of selective breeding has produced the ornamental gold form known worldwide, the wild-type fish is more a silvery colour. Introductions normally occur when unwanted fish are released into the wild, though they have been stocked in coarse fisheries.
If the goldfish is introduced to a water with no predators, they can survive and breed - maintaining a gold colouration. If predators are present the gold form is rapidly removed or selected against, wild-type fish occur. If the two occur together it is possible for the goldfish to interbreed with Crucian Carp.

6. Rainbow trout:Oncorhynchus mykiss

This trout species was introduced into the UK from the USA, also into New Zealand and Australia. It is used for stocking trout fisheries and for supplying the food industry. Mainly it remains contained in specific lakes, gravel pits, reservoirs etc.
Escapees may compete for food and habitat with Brown Trout. The Rainbow Trout will eat almost anything, from bottom-dwelling invertebrates, to fish and insects from the surface. As they mature they become increasingly piscivorous.
They have a high growth rate, but tend not to breed in the UK, as they require warm water temperatures. Another reason for no breeding is that now, most farmed fish are usually triploid and sterile - they use all their energy input to grow rather than to reproduce.

7. Zander:Stizostedion lucioperca

The Zander is a predatory fish, similar in shape to the Pike, but resembling a Perch, hence the common misconception that it is a hybrid of the two. It is actually a member of the Perch family. Zander were first introduced into UK in 1878, to private lakes at Woburn Abbey. 97 Zander were legally introduced into the Great Ouse Relief Channel in 1963, by Anglian water. Zander then rapidly spread through the drainage system.
Initially they were blamed for a reduction in coarse fish (such as Roach and Bream) but now are more widely accepted. They may compete with native Pike and Perch for food. They may deplete cyprinid stocks, but the extent of their actual influence is uncertain.
They are a highly adaptable species, thriving in large, slow flowing rivers and drains, also in ponds, lakes and gravel pits. Zander have excellent vision, making them well-suited for life in deep, dark waters, or in turbid waters, where other predators may not succeed.
A similar species known as Walleye is found in the USA.

Worldwide, freshwater ecosystems have had many species introduced, usually to the detriment of the system, flora and fauna. Anywhere with freshwater ports used for global trade, or even regional trade is at risk from introduced species. The introductions are also made for various reasons, and if containment measures are not implemented then the species can spread.
Measures to reduce the likelihood of species transferral are being implemented in the Great Lakes of America, with other countries to follow suit. Introduced organisms may become very successful if conditions are suitable for them, if not they will die out.
The problem of introduced species is not confined to freshwater habitats. Saltwater and terrestrial habitats have also had many introduced plant and animal species - again usually to the detriment of the native flora, fauna and ecosystems.

LINKS:

Exotic species introductions
USA and other Immigrant species-includes info on Australia.
Virtual Biodiversity Library
English Nature

References:

Balcom, N. C., 1994. "Aquatic Immigrants of the Northeast, No. 1: Introduced Species", Connecticut Sea Grant College Program

"A Field Guide To Aquatic Exotic Plants And Animals", 1995. Minnesota Sea Grant Program

Bochenek, E., Vol.1 No.1 Spring 1996. "New Jersey 'News'-Ance", New Jersey Sea Grant

Morton, B., "The Aquatic Nuisance Species Problem: A Global Perspective and Review" Department of Ecology and Biodiversity, and the Swire Institute of Marine Science, University of Hong Kong.

Cihar, J. "A Guide to Freshwater Fish" Treasure Press, 1991.

Moss, B. "Ecology of Freshwaters - 3rd Edition"Blackwell Science, 1998.