Didymosphenia geminata update

24th December 2004

Summary

1. Major points to note on Biosecurity New Zealand's (BNZ's) response to the detection of a freshwater alga, Didymosphenia geminata (Didymosphenia), in two Southland rivers, include:

• BNZ convened a Technical Advisory Group to assess impacts and identify appropriate management options;
• Didymosphenia is not able to be eradicated in the short term although it should be possible to slow its spread;
• BNZ has decided to initiate measures to attempt to contain Didymosphenia to affected rivers to give Biosecurity New Zealand (BNZ) time to determine longer-term management options;
• Containment measures will consist of a vigorous awareness campaign supported by the Unwanted Organism powers of the Biosecurity Act 1993
• A recently completed survey has indicated with a high probability that Didymosphenia is not present in the surrounding rivers that have been sampled. This adds additional weight to ensuring the measures to attempt containment are robust.

2. BNZ is continuing to work closely with Environment Southland, Fish and Game, Department of Conservation and Meridian Energy on this issue.

Background

3. Brief history:

• Didymosphenia is a freshwater alga detected in two Southland rivers, the Waiau and the Mararoa;
• Didymosphenia was first detected on 15 October 2004 during routine surveys conducted on behalf of Meridian Energy;
• It is considered to be a recent new introduction to New Zealand;
• Anecdotal information from overseas suggests that the alga could have ecological, aesthetic and economic impacts as well as being a nuisance from a human health perspective;
• Many of New Zealand waterways may be susceptible to invasion; and
• BNZ has been involved since 22 October 2004.

Initial Response

Information collection

4. BNZ has convened a Technical Advisory Group (TAG) to assess the impacts of Didymosphenia and identify appropriate management options. The TAG consisted of three local experts from NIWA and the Department of Conservation and two international experts (via teleconference).

5. The TAG has considered that:

• Didymosphenia is an exotic organism to New Zealand;
• There is no known eradication method at this stage;
• There are definite grounds for concern in terms of potential impacts for New Zealand, based on observations in the northern hemisphere, including impacts on the food chain within the rivers;
• The algae may already be present in other streams; (however microscopic sampling subsequent to the TAG meeting has not detected Didymosphenia outside of the Waiau and Mararoa rivers);
• Didymosphenia is likely to have been present in the Waiau and Mararoa Rivers for at least two years and has been blooming in these rivers for at least the last three months; and
• The presence of the algal blooms in the river systems will significantly increase the likelihood of spread to unaffected rivers.

6. The TAG has recommended that BNZ undertake actions including:

• Containment of Didymosphenia to the existing affected rivers;
• Assessment of the extent of Didymosphenia outside its known locations-with specific attention to the microscopic stage; and
• Research to assess:
  • the efficacy of potential methods to treat boats, fishing gear and other items coming in contact with the affected rivers
  • habitat preferences and environmental conditions that trigger blooms
  • the likely location around New Zealand where Didymosphenia could establish and bloom

Management programme

Containment

7. The principal management activity, at this stage, is containment. This could be achieved either by:

• prohibiting access to the two affected rivers; or
• managing the movement of gear, equipment and other items that have been in contact with affected rivers.

8. BNZ officials decided to manage the movement of equipment, gear and other items, rather than prohibit access, because the only way to effectively prohibit human access is to have a Biosecurity Emergency declared under Part VII of the Act. For a number a practical reasons outlined below, this is not considered desirable:

• Prohibiting human access would not guarantee that Didymosphenia would not spread from the affected rivers as birds and other animals could potentially spread this organism;
• Access is not a problem, per se, it is the movement of people, equipment, gear, and other items from affected to unaffected catchments that poses the risk;
• This organism cannot be eradicated in the short term and closing two rivers over the long term was considered not practicable;
• The affected rivers are a valuable source of income (e.g. tourism, fishing) and recreation for people in the surrounding area. Closing the rivers could have a significant impact on them without a commensurate benefit as Didymosphenia cannot be eradicated in the short term; and
• Effective containment could be achieved through education of visitors to the rivers about the problem and prudent control measures to take in respect of equipment, gear and items that come in contact with the affected waters.

9. BNZ is proposing to contain Didymosphenia through:

• An awareness programme providing information on Didymosphenia, its impacts and methods to prevent its spread;
• On the ground personnel to disseminate information and assist people to take measures to avoid spreading Didymosphenia from affected to unaffected rivers; and
• Provision of a vehicle with treatment facilities in the affected area, to help people clean their equipment, gear or other items that may have come in contact with affected rivers.

10. The programme will be implemented over the Christmas period to ensure that people using the area are well informed of the problem, their responsibilities under the Biosecurity Act, and how to take action.

Delimitation

11. A survey has recently been undertaken to determine whether the microscopic stage of Didymosphenia is present in the rivers surrounding the affected Waiau and Mararoa rivers (as suspected by the members of the TAG). The survey has not detected any sign of Didymosphenia outside of the Waiau and Mararoa catchments, adding weight to ensuring the measures to attempt containment are robust.

12. Further work will also be undertaken to assess Didymosphenia potential distribution. Information on its current and potential distribution will inform future management decisions.

Research

13. The main research needed at this stage is to determine the efficacy of possible treatment / cleaning methods for equipment, gear and other items that have come in contact with the affected rivers. Due to timing constraints, prior to Christmas BNZ has contracted NIWA to undertake a rapid assessment of the treatment / cleaning methods considered most likely to be effective. After Christmas, BNZ will review the need for a more rigorous assessment of the efficacy of the treatments.

Next Steps

14. Eradicating Didymosphenia is not likely to be possible. The future direction of the programme is likely to involve slowing its spread and mitigating its impacts. To work towards this the proposed next steps are:

• Completing the assessment of treatment methods for equipment used in affected rivers;
• Undertaking a study to investigate Didymosphenia's habitat preferences (an autecology study);
• Determine the likely distribution of Didymosphenia in New Zealand and identify values at risk;
• Determining the management options (with advice from the TAG): and
• Analysing the management options and determining a preferred option.