4 Inland water | 3 Pressures affecting inland water environments | 3.4 Pests and invasive species
State of the Environment 2011 Committee. Australia state of the environment 2011.
Independent report to the Australian Government Minister for Sustainability, Environment, Water, Population and Communities.
Canberra: DSEWPaC, 2011.
At least 80 introduced animal species have established populations on the Australian continent. Assessing invasive animals in 200853 stated that invasive animal species are one of the top three greatest threats to threatened species and ecosystems—mainly by competing for, or destroying, habitat and food resources—and that they continue to colonise new areas. Some of these species were initially established in past centuries and continue to expand their ranges (e.g. the cane toad spreading into Western Australia in February 2009; Figure 4.18), but new threats have also emerged, such as red-eared slider turtles and tilapia. Carp were found to occur in 11.5% of Australian rivers. In addition to carp and cane toads, feral pigs were identified as nationally significant invasive animals by the Australian Vertebrate Pests Committee, due to their impact on inland river systems (especially wetlands).
Southern Australia and New Zealand, considered together, represent one of six major invasion ‘hot spots’, where non-native freshwater fish species represent more than one-quarter of the total number of fish species in river systems, and where the proportion of native fish species that have a high risk of extinction in the wild is the highest.54 In New South Wales, three alien species—common carp, gambusia and goldfish—are present in all inland rivers. Redfin perch, brown trout and rainbow trout are also widespread. Carp are overwhelmingly dominant (Figure 4.19), making up 87% of alien fish biomass and 58% of total fish biomass. Carp and gambusia were the dominant species in all lowland rivers in the Murray–Darling Basin.
Source: Reid Tingley, University of Sydney, unpublished data, and Kearney et al.55
Figure 4.18 Current and predicted distribution of cane toad (Bufo marinus)
In February 2009, cane toads expanded into the Kimberley region of Western Australia. Predictions of the cane toad’s future range were based on long term monthly averages of daily maximum and minimum air temperature, wind speed, cloud cover and relative humidity, rainfall totals and a solar radiation model, which were used to drive mechanistic models of microclimatic conditions and their physiological consequences for cane toad activity, development, survival and reproduction.
Source: National Land & Water Resources Audit53
Figure 4.19 Distribution of common carp (Cyprinus carpio)
The climate of most of southern and central Australia is considered highly suitable for carp.
Australia has about 30 000 species of legally imported plants; of these, about 2700 species have become naturalised. About 300 species are declared weeds,56 which alter the natural environment and subsequently destroy habitat for native species. Of the Weeds of National Significance,57 nine invasive plant species are of particular concern to inland water ecosystems (Figure 4.20):
- alligator weed (Alternanthera philoxeroides)
- cabomba (Cabomba caroliniana)
- salvinia (Salvinia molesta)—see Figure 4.21
- hymenachne (Hymenachne amplexicaulis)
- mimosa (Mimosa pigra)
- pond apple (Annona glabra)
- willow (Salix spp.)
- blackberry (Rubus fruticosus)
- athel pine (Tamarix aphylla).
Alligator weed, cabomba, salvinia and hymenachne are all aquatic weeds.
Source: Australian Government Department of Sustainability, Environment, Water, Population and Communities, 2011
Figure 4.20 Number of the nine weed species of national significance found in each river basin, which are of particular concern to inland water ecosystems
Source: Weeds of National Significance,57 with original digital occurrence data supplied by the states and territories and nationally collated through the National Land & Water Resources Audit
Figure 4.21 Distribution, spread and management actions for Salvinia molesta
Salvinia is a floating aquatic weed that can cover entire water surfaces with a thick mat of vegetation, shading submerged plant life and impeding oxygen exchange, making the water unsuitable for fish and other animals. The national response to this introduced weed shows what can be accomplished with an effective control option (in this case developed by CSIRO using a natural biological agent—Cyrtobagous salviniae), and national strategy and commitment. Nevertheless, complete eradication has not yet been possible.
|Component||Summary||Assessment grade||Confidence in grade||Confidence in trend|
|Very high impact||High impact||Low impact||Very low impact|
|Pressures resulting from climate variability and climate change||Widespread and unprecedented drought across southern Australia over the past decade or more has greatly affected inland water ecosystem condition. Flooding since 2009 has broken the drought in the south-east of the continent, but the drought continued (as of early 2011) in the south-west
There is substantial scientific evidence of a component of change towards a drier climate across southern Australia and a warmer climate nationally. Drier landscapes have the potential for increased rates of sedimentation due to decreased vegetative cover, exacerbated by the potential for more frequent and intense storms
|Water resource development||Historical allocations of surface water and groundwater have changed the ecological character of many river and wetland systems across southern Australia; development pressures are generally much less in the northern half of the continent
Recovery of water for increased environmental flows in the Murray–Darling and Snowy basins has reduced this pressure on some inland water ecosystems
Most new water for Australian metropolitan areas will come from resources other than development of new inland resources—sources will include reuse and seawater desalination, improving run-off and recharge into existing infrastructures, and trading with existing users
|Land use and management||For most of Australia, historical land clearing for dryland agriculture and locally intensive agricultural land uses continue to place river systems under pressure from nutrient run-off, sedimentation and salinisation
The growth of the peri-urban fringe around major metropolitan areas places great pressure on local waterways and can involve the irreversible drainage of local wetlands
Riparian degradation by livestock and feral pests is an ongoing impact
|Pests and invasive species||Vertebrate pests continue to impact most inland water systems across the continent, through grazing-related impacts, direct ecological competition or as a hazard to native predators (as in the case of cane toads)
Waterway and floodplain weed infestations are widespread but of variable local impact
|Recent trends||Improving||Stable||Confidence||Adequate high-quality evidence and high level of consensus|
|Deteriorating||Unclear||Limited evidence or limited consensus|
|Evidence and consensus too low to make an assessment|
|Grades||Very low impact: There are few or negligible impacts, and predictions indicate that future impacts on the environmental values of regions are likely to be negligible|
|Low impact: There are minor impacts in some areas, and predictions indicate that future impacts on the environmental values of regions are likely to occur, although they will be localised|
|High impact: The current and predicted environmental impacts are significantly affecting the values of regions, and predictions indicate serious environment degradation within 50 years|
|Very high impact: The current and predicted environmental impacts are widespread, irreversibly affecting the values of regions, and predictions indicate widespread and serious environment degradation across the region within 10 years|