Issue: Response of biota - Invasive species
This is an issue under the Inland waters theme of the Data Reporting System.
An invasive species is a species occurring, usually as a result of human activities, beyond its accepted normal population or distribution, and which has a potentially negative impact on the resident ecosystem. Even species endemic to an area can become invasive as a result of changes in environmental conditions which favour them over another species. More often, invasiveness occurs when new species are intentionally or accidentally introduced to an environment by human action, and thrive in that environment to the potential detriment of other species. This is most likely to occur in environments that have been intentionally altered to favour introduced species, for example, by agriculture. Habitat modification, disturbance and destruction, including changed fire and water regimes, can cause changes in species distribution, favouring one species over another and leading to invasiveness by some species.
Alteration of an established number, population and distribution of species contributing to an ecosystem can result in a reduction in overall species abundance and diversity. Niches once occupied by a range of species can be taken over by a particularly successful species. As a result, access to available food or shelter may be reduced for less successful species, and impacts on one species can then affect other species that may be dependent on the diminished species.
Invasive species include diseases, fungi and parasites, terrestrial and marine animals (including insects and other invertebrates) and plants and can place pressure on terrestrial, marine and freshwater biodiversity.
- IW-37 Examples of carp pressures and measures for removal and/or commercial catch
Native fish numbers began declining in the 1800s, long before carp appeared, with the introduction of agricultural, mining and other practices that were not consistent with long term sustainability (eg impact of fishing, river-flow control for irrigation, deliberate clearing of aquatic vegetation, cattle hoofs on river or stream banks and removal of groundcovers and understorey near waterways). This altered the aquatic environment so that it was well suited to carp but no longer well suited to native fish. However, once present, carp can have their own impact on waterways.
The carp’s feeding habits can impact on inland waters by denuding riverbeds of vegetation. The fish suck up mud, which is re-suspended when it exits the digestive tract or is spat out again. This can cause significantly higher levels of turbidity and siltation and can block light necessary for photosynthesis from aquatic plants. Without aquatic plants, the waterway becomes more turbid and nutrients remain mobilised instead of being absorbed by plants. Algal blooms resulting from an excess of nutrients can further reduce the amount of light penetrating the water, further hindering photosynthesis.
Examples of pressures from carp, along with either positive or negative changes in these pressures where control or harvesting measures are taken may provide insights into the actual impacts of the animal and the effectiveness of responses.
- IW-38 Cane toad distribution
In 1935 cane toads were released throughout cane growing areas in Queensland to control cane beetles. They did not control the beetles but ate large numbers of beneficial insects.
The cane toad has a large gland behind the head that can exude a poisonous milky substance when the toads are disturbed. Cane toad poison is highly toxic to many animals. Aquatic animals are affected because the eggs and tadpoles of toads are also poisonous. Predators are vulnerable to the toads. Since introduction the cane toad has increased its distribution. Changes in the extent of its distribution provides some indication of the area where the species could become invasive.
- IW-39 Examples of significant wetland weeds
In the absence of detailed data on the distribution and actual impact of various wetlands weeds, examples of how particular weeds can affect the aquatic environment are worthy of consideration.
- LD-40 Current research into pressures and contributions of naturalised introduced species
Other indicators for this issue do not indicate whether naturalised populations are exerting pressure on native species or ecosystems. Current research into this issue, even in the absence of national data, may shed some light on these effects.
- BD-09 The change in extent of selected nationally significant invasive species
Modification of freshwater environments for irrigation, extraction, storage, recreation, or any other human purpose, can involve removing resident species and introducing new species. This unbalancing of ecosystems can cause some species in the modified environment to become invasive. While it is difficult, on the basis of any available data, to establish whether and how invasive any species might be, changes in distribution and population of one species may be an indicator of more profound ecological changes. Additionally, where there is a concern that a particular species is behaving invasively, changes in its distribution may signal an increase in area at risk, either from the species itself, or from the environmental modifications that are favouring its expansion.
- BD-10 Examples of native species whose populations have declined where various invasive species have established resident populations
Changes in population and/or distribution of either native or introduced species may be indicative of more general changes in the condition of freshwater systems, whether the cause of the change is habitat modification, species introduction, or any other pressure. Compiling data on such correlations may also enable the development of studies which control for other pressures and thus provide insight into the actual impact of naturalised species on condition of inland waters.
- Biodiversity - Pressures on biodiversity- Invasive species
- Land - Direct pressure of human activities on the land- Species introduction and species change
- Inland Waters - Human response - policy and management- Management of aquatic biota and biodiversity
- Coasts and Oceans - Direct pressure of human activities on coasts and oceans- Direct pressure of shipping
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