Case study – Responding to a range extension of a marine pest

Mediterranean fan worm (Sabella) is an unwanted organism under the Biosecurity Act 1993. It is a filter-feeding tube worm which can form dense colonies and has the potential to alter nutrient cycles and compete with native species for food and space. This fan worm grows rapidly in New Zealand waters, particularly in Auckland and Whangarei, where it infests vessel hulls, artificial structures and natural substrata. Sabella can potentially impact on marine farms and clog fishing nets and dredges.

Sabella was first detected in Lyttelton in 2008 during a targeted surveillance programme. During eradication attempts in Lyttelton, populations of fan worm were detected in Auckland’s Waitematā Harbour, at densities suggesting it was well established there. The MPI for Primary Industries decided that it was no longer feasible to attempt eradication of the organism from New Zealand. Since eradication efforts were abandoned in the Waitematā Harbour, Sabella has dramatically increased its range there. Recent incursions to new regions, such as Whangarei, suggest that Sabella has been moved by vessels coming from Auckland. However, individuals from the small population in Lyttelton Harbour are removed when found during the targeted surveillance programme, and this population has remained small (typically, no more than one or two individuals are found during each six-monthly survey).

Under the National Pest Management Plan of Action, regional councils assume the default lead role when responding to incursions of marine pests that are already established in New Zealand. The MPI has decided to support a number of regional councils where Sabella has recently been detected as outlined in Figure 5.x below. The current approach is aimed at slowing the spread of Sabella while a national marine pathways management plan is developed. 

Region

Approach

Northland

  • Sabella was discovered in Whangarei Harbour in 2012
  • In early 2014, further populations of the fan worm were discovered at additional sites, after two years of attempted eradication
  • Approaches used to slow the spread of the fan worm include developing charters with local vessel haul-out operators and marinas, profiling vessels suspected of harbouring Sabella, and ensuring infested vessels are defouled as soon as possible
  • The Northland Regional Council has recently sought science advice on the feasibility of managing Sabella at infected sites in Whangarei to ensure that it is not spread from the harbour

Waikato

  • The Waikato Regional Council and MPI jointly responded to the detection of heavy infestations of Sabella on two barges moored in the Coromandel Harbour, following a notification from a member of the Marine Farming Association in April 2013
  • Urgent action was taken to remove the fan worms as the organism spawns over a prolonged period during winter
  • A detection survey over the wider area was undertaken to ascertain whether there was an established population 
  • All detectable mature fan worms were removed from the barges and no fan worms were found on the substrate after thorough searches of the wider area 
  • Barges were then moved to a region where fanworm was established
  • Surveillance later in 2013 detected a small colony of fan worms on a mooring block in the vicinity of where the infested barges had been, which were removed
  • Surveillance will continue in the harbour
  • Council will explore ways of collaborating with adjacent regional councils to minimise the risk of further incursions into Coromandel and other harbours within its jurisdiction

Bay of Plenty

  • A scientist conducting survey work in Tauranga Harbour detected a single Sabella on the rocky substrate of Pilot Bay and notified MPI in September 2013
  • The Bay of Plenty Regional Council and MPI jointly responded to this detection and a delimiting survey was carried out at all high risk sites in the harbour, including in the vicinity of the detection, moored vessels and moorings, wharves at the port and the two marinas during the next two months
  • A small number of Sabella were found in one of the two marinas and a single Sabella was found on the hull of a yacht moored in the vicinity of the original detection. The owner was contacted and voluntarily agreed to have the yacht urgently slipped and defouled. 
  • During the Marine High Risk Site Surveillance Programme in May 2014, a small number of Sabella were detected in the two marinas
  • The regional council quickly responded the following week, again with support from MPI, by surveying both marinas
  • Further Sabella were found in low numbers
  • The recent detection of Sabella suggests that some were most likely missed during the first survey, particularly where water visibility was low, as there are high levels of biofouling species in the marinas and the fan worms are small in size
  • The regional council has developed a marine biosecurity management plan to respond to future incursions of marine pests and to carry out surveillance programmes within the council’s harbours

Nelson

  • In November 2013, a single Sabella was found in the Nelson Marina during the Marine High Risk Site Surveillance programme
  • The Nelson City Council and MPI jointly responded and implemented a delimiting survey of the entire marina and other high risk sites in and around the port during the same month as the initial detection
  • This survey found and removed twelve Sabella of varying tube lengths
  • The agencies decided to undertake a second survey prior to the 2014 winter, in case some animals were missed, which proved to be a prudent measure as a further twenty-two fan worms were found
  • The council has decided to continue surveillance for the fan worm over the next year. The total number of fan worms collected (less than forty), combined with the relatively confined area they were found (the central area of the marina), gives confidence that this incursion can be suppressed

Marlborough

  • In February 2014, a research scientist surveying fouled vessels in Waikawa Bay, Marlborough Sounds collected Sabella from a heavily fouled yacht on a mooring 
  • The Marlborough District Council and MPI agreed to jointly respond to the incursion 
  • The Council arranged to get the vessel slipped and defouled within two weeks of detection, with the agreement of the owners
  • Tracing showed the yacht had relocated from Auckland to Waikawa Bay approximately one to two years previously, suggesting that it had probably become infested in Auckland
  • A delimiting survey was undertaken in early April and all high risk areas, including the Waikawa Marina, were inspected with no further Sabella found 
  • The Marine High Risk Site Surveillance programme included the Waikawa Marina during June as part of its usual programme, with no detection of Sabella 
  • Targeted surveillance for Sabella will search all the high risk sites later in 2014

The four most recent incursions demonstrate that the goal of local elimination is more likely to be successful if surveys and removal of the Sabella are undertaken soon after detection and prior to reproductive maturity. However, the risk of incursions from newly arriving infested vessels remains. Large numbers of mature Sabella were recently removed from the hull of a coastal freighter that travels between New Zealand ports. A combination of pathway management, readiness and response will be necessary to ensure Sabella does not spread and establish into new areas. 

Last updated at 2:11PM on February 25, 2015