15th Feb 2023 |
To slow the introduction of sea spurge from Victoria and Tasmania to beaches in New South Wales, the NSW Government has co-invested with CSIRO in a project to release a biocontrol agent along the Victorian and Tasmanian coastlines. Here's an update of the program so far, including community participation through community-led releases.
Authors: Caroline Delaisse, Jon Marsden-Smedley, and Gavin Hunter
Sea spurge (Euphorbia paralias) is a highly invasive coastal weed along the southern coastline of Australia. Native to Europe and North Africa, sea spurge was likely introduced to Australia in the early 20th century through ballast water of ships arriving from Europe. Since then, sea spurge has gradually spread along the southern coastline where it infests dunes and foredunes outcompeting native vegetation, reducing available nesting areas for native shorebirds, and exuding a latex when damaged, which is a toxic irritant to humans and animals. Because of these negative impacts, sea spurge has reduced the amenity value of many beaches along our southern coastline. Fortunately, a highly specific biological control agent of sea spurge has been identified by Australia’s National Science Agency, CSIRO. The biological control agent, a fungus called Venturia paralias, infects the leaves of sea spurge, forming large dark brown circular leaf lesions that progress to the stem and reduce plant performance. Following comprehensive host-specificity testing of the biocontrol agent by CSIRO, the Australian regulator recommended the release of the fungus in November 2020 into the Australian environment to assist in the management of this significant environmental weed.
Image: Generalised infection process of sea spurge by its fungal biological control agent, Venturia paralias
To slow the introduction of sea spurge seed via ocean currents from Victoria and Tasmania to beaches in New South Wales, the NSW Government through its Environmental Trust has co-invested with CSIRO in a project to release the biocontrol agent along the Victorian and Tasmanian coastlines. This three-year project (2021-2024) encompasses two parallel parts that run simultaneously, consisting of (1) community-led releases of the agent at many sea spurge infestations along the coastlines of Victoria and Tasmania and (2) controlled releases and monitoring of the agent at specific sites in Victoria and Tasmania, led by CSIRO.
Community-led releases of the biological control agent in Tasmania
CSIRO engaged with media during the last quarter of 2021 to distribute information, through various media channels, about the sea spurge biocontrol project so that various community organisations would become aware of the project and learn how to become involved. Several community groups expressed interest to CSIRO in receiving the fungus to undertake releases in areas that were heavily infested by the weed. Registered community participants currently include private citizens, government agencies and members of several volunteer community groups (e.g., Bushcare, Coastcare, Friends groups, Landcare etc.) based in Tasmania.
Release kits containing the biocontrol agent were dispatched to registered participants from December 2021, and dispatches have continued since. A total of 124 kits have now been supplied to Tasmanian participants to release the biocontrol agent on sea spurge plants in the field. Registered community members were provided with a release kit that contained the dried culture of the fungus from which they could prepare a spore suspension solution to spray onto sea spurge plants. Detailed instructions and a video tutorial are also provided to participants to ensure a successful release of the agent.
Ten weeks after inoculation, community participants were encouraged to return to the release site(s) and record the presence or absence of characteristic dark brown to black leaf and stem lesions caused by the biocontrol agent. To date, 43% of community-led biocontrol releases in Australia have been carried out in Tasmania and follow up on successful infection is still required for approximately 50% of these releases.
From community feedback it is clear that environmental context plays an important role in the successful infection of sea spurge by the biocontrol agent. Infection of the weed by the agent has occurred at some community release sites but not at others. This is likely due to a range of factors including the time of release, the aspect of the release site, prevailing temperature and humidity, and the specific season. As more information is obtained from community participants, CSIRO researchers will be able to determine the critical factors necessary for successful establishment of the agent, which will enable optimisation of future releases of the fungus.
Infographic: Numeric information on the community participants and number of releases of the sea spurge biocontrol agent in Tasmania
Sea spurge monitoring sites
CSIRO worked closely with the Tasmanian Parks and Wildlife Service (TPWS), who supported the release of the biocontrol agent and who suggested various sea spurge infestations where dedicated monitoring sites could be established for the duration of the project. Following approval from TPWS, three sites were identified on the TPWS estate and initial field releases of the sea spurge biocontrol agent in Tasmania commenced during October 2021 with the establishment of three monitoring sites (see below image) and release of the biocontrol agent at these sites. Each monitoring site consisted of three 10-metre transects with five 1m2 plots per transect. Two monitoring sites are located on the north coast of Tasmania while a third site is situated on the mid-west Tasmanian coast. Since these initial releases, two detailed assessments of the three monitoring sites have occurred, the first during April/May 2022 and the second during November 2022.
Following release of the biocontrol agent, initial assessments of the three monitoring sites during April and May 2022 indicated that the biocontrol agent was present in 84% of the plots across the three monitoring sites. Here, the presence of the agent was confirmed by the characteristic dark brown to black stem lesions on infected sea spurge plants in the monitoring plots. During the November assessments an interesting observation was made through the identification of a different infection symptom on infected sea spurge plants. Instead of stem lesions, the biocontrol agent had subsequently sporulated from the stem lesions and infected the leaves of sea spurge plants. In this case, the biocontrol agent was present in 95% of the plots across the three monitoring sites as evidenced by plentiful dark brown concentric to angular leaf lesions on sea spurge plants. Along with the leaf lesions, older stem lesions were still observed at 44% of plots but it was clear that the agent had transitioned to a different phase of its infection cycle on sea spurge.
In addition, evidence was found that the agent had naturally spread outside of the monitoring sites. For example, the agent was detected as far as 250 metres to the south (downwind) from one of the monitoring sites on the north coast and 75 metres to the north and south of the monitoring site on the west coast. From this initial assessment data, the biocontrol agent is still present at the release sites and has therefore successfully established at these sites. Furthermore, the agent has successfully cycled through infection stages to produce both types of characteristic infection symptoms and has now begun to spread locally outside of the monitoring plots to infect other sea spurge plants in the vicinity.
Image: Tasmanian locations of community-led field releases of the sea spurge biocontrol agent and specific monitoring sites that will be used for quantitative assessment of the biocontrol agent.
Community participation in this project has been vital to the successful release of the biocontrol agent in Tasmania and Victoria. CSIRO is eager to continue engagement with community organisations for additional releases of the agent during Autumn and Spring of 2023. Community organisations involved in coastal weed management, and who have the necessary approvals from land owners and managers, are encouraged to contact Caroline Delaisse ([email protected]) or Gavin Hunter ([email protected]) to become registered as community participants in the project and receive release kits of the agent for field releases. For further information on the sea spurge biocontrol project, readers are invited to visit the project webpage (https://research.csiro.au/nswweeds/sea-spurge/). To learn more about other CSIRO weed biocontrol projects currently underway, readers can access the following website https://research.csiro.au/weed-biocontrol/
Further detailed assessments of the agent at the monitoring sites and surrounds will continue during 2023 and 2024 to obtain quantitative data on agent establishment, its initial impact and its spread across local sea spurge infestations. This data will assist CSIRO researchers to determine the overall success of the environmental releases of the sea spurge biocontrol agent and the ways in which the agent could assist in future management practices of sea spurge.
Funding acknowledgement: This project has been proudly supported by the NSW Government through its Environmental Trust