Risk analysis: Euphorbia paralias - sea spurge Technical Report
- Author
- Duthie, C.
- Year
- 2012
- Publisher / Organisation
- Ministry for Primary Industries
- Pages
- 21
- Keywords
- Euphorbia paralias, sea spurge
- Summary
- Euphorbia paralias is a long lived herbaceous coastal plant native to North Africa, western Asia, and Europe and invasive in Australia. Seeds are buoyant and can be spread very large distances by ocean currents. Once established, E. paralias develops dense infestations which prevent natural sand movement, altering dune communities, threatening some rare coastal plants, and contributing to the decline of some species of nesting shore birds. Euphorbia paralias has been reported as invading pastoral land adjacent to coastal areas in Australia reducing pasture available for stock grazing. Establishment may change coastal sand movement processes which may exacerbate coastal hazards such as erosion. Additionally, the latex sap of E. paralias is considered poisonous and causes skin and eye irritation. Euphorbia paralias has been detected at one site near Aotea Heads Scientific Reserve, Waikato, but is not considered to be established in New Zealand. This population is considered to be as a result of seed movement on ocean currents from Australia. Following this detection a risk analysis was requested by the Ministry for Primary Industries Response Manager for Euphorbia paralias. This analysis follows the Biosecurity New Zealand Risk Analysis Procedures (MAF 2006) but has been written to support the planned activities, and inform decisions on the management options. The climate in New Zealand is similar to the climate in native range of E. paralias and much of its introduced range in Australia. Euphorbia paralias is capable of establishment throughout much of coastal Australia, particularly Tasmania. Given its native and introduced range, it could be expected that climate would be no barrier to establishment throughout coastal New Zealand. Between the first detection in Australia and the present day, E. paralias has spread throughout the entire coastal regions of South Australia, Victoria, southern New South Wales and Tasmania. Given this rate of spread in Australia, the large numbers of seed produced, and the multiple pathways of spread it could be expected that E. paralias could spread rapidly to most coastal regions of New Zealand within the next 50 years. Movement around New Zealand from an established population is highly likely as a result of a combination of coastal currents, bilge and ballast water, and contamination associated with recreational vessels, cruise ships and commercial vessels, and on-shore recreational activities which may transport seeds, plants or root fragments. While it is not possible to prevent the arrival of seed it is possible to reduce to zero density populations that are detected, thereby mitigating the consequences of establishment. As there are no management options for stochastic events such as „natural dispersal‟ of invasive seeds or plants to New Zealand, focus will need to be on management of the current population, and future infestations and populations when they are detected. Furthermore establishment of at least some future populations is likely to be in remote and difficult to access locations and populations may be relatively large before they are detected. Exclusion (maintain zero density) is recommended as an option as opposed to eradication. The exclusion option recognises that new incursions are likely and therefore the best intervention point is the removal of populations as they are detected. Eradication is unlikely to be achievable as the risk of establishment from new incursions is high. Eradication cannot be achieved if new incursions are likely, as these new incursions would potentially negate the additional effort required of an eradication programme.