AQUATIC ECOSYSTEMS The integrity of aquatic ecosystems is being challenged worldwide by invading species. Affected aquatic ecosystems include estuaries,

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  • AQUATIC ECOSYSTEMS The integrity of aquatic ecosystems is being challenged worldwide by invading species. Affected aquatic ecosystems include estuaries, fresh water, marine and wetlands. Species are introduced by means of ballast water, hull fouling, infrastructure (canals), aquaculture and many other pathways. %20page%202.htm Aquatic ecosystems
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  • FRESHWATER Some examples include the Nile perch, sea lamprey, zebra mussel and brown trout. Tolerant of a wide range of environments, the brown trout continues to be stocked for recreational fisheries in rivers and streams in the USA. The species reproduces well, and predates or competes with many indigenous fish and amphibian species. n-release2.html Freshwater
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  • A significant invasive in Europe is Leidys comb jelly (Mnemiopsis leidyi). It was probably released from ballast waters. It feeds on zooplankton, and since there were no predators in the Black Sea, food webs were damaged, leading to the collapse of anchovy and other fisheries a significant ecological as well as economic impact. rnagie/Carnagie/EarthScience/Ocean/EarthCh5Ocean4.htm MARINE Marine
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  • The US receives more than 79 million tons of ballast water from overseas each year. Ballast tanks carry a diverse community of organisms, resulting in many biological invasions. Pathogens are common in coastal waters and can also be transferred in ballast water (Ruiz et al, 2000). Ballast water is surprisingly not the most significant pathway of IAS introduction for the US. Stocking and aquarium release are the most significant pathways for fishes, with baitfish and food importation close behind. BALLAST WATER Ballast water treatment technologies include: Ozonation treatment UV Irradiation Natural Product Biocide Deoxygenation Ballast water
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  • Barnacles, mussels, sponges, algae, sea squirts etc. attach themselves to the hulls of ships, fouling them. Invasions can occur when these fouling organisms come in contact with structures in a new port or harbour, or release their larvae into new waters. nt/water/water_quality_monitoring/projects/introduced _marine_pests/ HULL FOULING Historically hull fouling was considered a primary vector for transporting species. However, the modern use of metal hulls and anti-fouling paints, decreased port residency times and faster ship speeds, contribute to reduced hull fouling (Marine Invasions Research Lab). Hull fouling
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  • The invasion of water hyacinths in Zambia is choking lake, river and wetland systems such that local fishing economies are devastated and hydroelectric facilities have been damaged. WETLANDS Wetlands
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  • Most of the previously forested lowland systems on the drier sides of Hawaii are now dominated by the invasive fountain grass (Pennisetum setaceum). This grass has severely altered the ecosystem dynamics of these arid regions by suppressing native vegetation and promoting fires that have proved devastating to the native flora (Cabin et al, 2000). TERRESTRIAL ECOSYSTEMS Terrestrial ecosystems
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  • The rapid invasion and spread of alien trees and shrubs of Acacia, Hakea and Pinus species over large areas of fynbos in South Africa, threaten hundreds of native plant species with extinction. They change fire and nutrient-cycling regimes, and greatly reduce streamflow from watersheds (Richardson, 2001). fire TERRESTRIAL ECOSYSTEMS cont. Terrestrial ecosystems cont.
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  • Parasites and pathogens Pathogens can undermine local food and livestock production, thereby causing hunger and famine. They often damage or kill indigenous species because these species have no defences against them. Chestnut blight eliminated American chestnuts from approximately 180 million acres in eastern USA. Ten moth species that could survive only on chestnut trees also suffered. Currently another introduced microbe (Phytopthora sp.) is causing the decline of most of the dominant hardwood forest species along the California coast. PARASITES AND PATHOGENS
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  • Rinderpest was introduced from Asia to Africa in 1889. The disease travelled 5000km in 10 years, killing more than 90% of Kenyas buffalo population, (Daszak et al, 2000). Some species populations still remain depleted or at risk. Rinderpest also wiped out most of the cattle in several regions, leading to widespread famine, huge economic losses and social unrest. Parasites and pathogens cont. PARASITES AND PATHOGENS cont.
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  • The bubonic plague spread from central Asia through north Africa, Europe and China using a flea vector on an invasive species of rat (Rattus rattus) that originally came from India. The viruses carrying smallpox and measles spread from Europe into the western hemisphere shortly following European colonisation (McNeely, 1996). Cholera was introduced into Peru in 1991 from Asia, from ship ballast water. In this case it coincided with an algal bloom, and then a redtide outbreak (dinoflagellates, which are the intermediate hosts of Vibrio cholerae), and sickened more than 300 000 people. Parasites and pathogens cont. PARASITES AND PATHOGENS cont.
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  • Genetic bottlenecks Colonization of introduced species often involves a population bottleneck because the number of initial colonists is often small. However, the loss of genetic variation through genetic drift and the inbreeding effect of small populations are thought to contribute to the increased extinction rate of small populations (Frankham and Ralls, 1998). So, a newly established population is likely to be much less genetically diverse than the population from which it is derived. The reduced genetic diversity can have two consequences: http://www.schneiderchildrensh ds/infectious/ INVASIONS AT THE GENE LEVEL Gene level invasions
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  • 1.Inbreeding depression may limit population growth and lower the probability that the population will persist 2.Reduced genetic diversity will limit the ability of introduced populations to evolve in their new environments If population bottlenecks are harmful (often leading to extinction), then why are invasive species that have gone through a founding bottleneck so successful? (Allendorf and Lundquist, 2003). ? ? ? ? ?? ? ? ? ? ? ? Gene level invasions cont.
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  • Many species cannot be assigned to either indigenous or alien status because of their global movements and lack of data to support or dismiss movements of species. These are defined as cryptogenic species (Carlton, 1996). Over the last 150 years, Phragmites australis distribution and abundance has increased dramatically in North America. CRYPTIC INVASIONS 11 halotypes were native to North America, 2 being widespread, with one of those being the most common (ancestral type). This type replaced native types and expanded into areas where historically P. australis did not grow. Cryptic invasions
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  • Japanese red alga (Polysiphonia harveyi) occurs on North American coasts of the North Atlantic. It is regarded as an alien in the British Isles and Atlantic Europe. Two separate invasive halotypes of P. harveyi were discovered, which originated from two separate introductions. Japanese alga
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  • Displacement of indigenous by invasive species through hybridisation is called genetic assimilation The invasive taxon is integrated into the gene pool of the indigenous species (Petit, 2004). Should hybrid plants resulting from the cross between an indigenous and alien plant be termed indigenous or alien? HYBRIDISATION Hybridisation According to Petit (2004), hybrids that have at least one alien parent should not be considered as indigenous since they would not be present without human intervention. This is the anthropocentric view. If the biogeographical view were accepted, hybrid taxa would be termed indigenous. (Why?)
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  • The loss of native fish due to hybridisation between indigenous and alien species has been known for more than 20 years (Miller et al, 1989). Other hybrids also occur e.g. between different alien species, between their ecotypes, and between previously isolated native species brought together by human activity. The mallard duck was introduced into SA from Europe, and they are capable of breeding with most species in their genus. They have been known to breed with the yellow-billed duck, which compromises the yellow-bills genetic integrity (Dean, 2000). ages/E05187.jpg HYBRIDISATION cont. Hybridisation cont.
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  • In the USA, the most abundant genotype of the alien Tamarix (which has invaded over 600 000ha of riparian and wetland habitats) is a novel hybrid between two introduced Eurasian species (Gaskin and Schaal, 2002). HYBRIDISATION cont. Hybridisation cont.
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  • Spartina anglica represents an example of a fixed hybrid form. Spartina alterniflora from eastern America was introduced i