Key Takeaways
- Divers conducting routine marine surveillance for the West Coast Regional Council (WCRC) observed an unknown aquatic organism in Jackson Bay in February.
- The organism was tentatively identified as Potamilla alba, a marine worm species previously recorded only at Banks Peninsula in 1951.
- Potamilla alba appears as dead‑white, 75 mm long worms with gills up to 10 mm, found in high densities (≈38 individuals per 10 mm²) around the Jackson Bay wharf.
- Biosecurity experts assess the worm as unlikely to pose a biosecurity threat; it is not considered harmful or invasive at this stage.
- The most plausible introduction pathway is transport on ship anchors or hull fouling, given the species’ tendency to form dense clusters that can be dredged by fishing vessels.
- Confirmation of the species remains pending; the current identification rests on a single taxonomist’s opinion and requires further verification.
- Ongoing marine surveillance and biosecurity monitoring are recommended to track any changes in abundance or distribution along the West Coast.
Discovery Details
In February, a team of divers carrying out marine surveillance on behalf of the West Coast Regional Council encountered an unfamiliar organism attached to structures in Jackson Bay. The sighting was noted during routine inspections aimed at detecting potential biosecurity risks to the region’s coastal ecosystems. The divers collected specimens and reported the find to the council’s biosecurity unit, prompting an immediate review of the organism’s identity and possible ecological implications.
Species Identification
The West Coast Regional Council’s biosecurity manager, Emily Rutherford‑Jones, explained that the organism was tentatively identified as Potamilla alba based on the assessment of a single taxonomist. This identification marks the first recorded occurrence of the species on the West Coast of New Zealand, although the World Register of Marine Species lists Potamilla alba as typically inhabiting New Zealand waters. Historically, the worm was first documented at Banks Peninsula in 1951, suggesting a long‑standing, albeit scarce, presence in the country’s marine fauna.
Physical Characteristics
Shanti Morgan, the council’s environmental science group manager, described the worms as “dead white” in colour, measuring approximately 75 millimetres in length. Each worm possesses feathery gills that can extend up to 10 millimetres, a feature typical of sabellid polychaetes used for filter feeding. The organisms were observed in remarkably high concentrations around the Jackson Bay wharf, with densities reaching up to 38 individuals per 10 square‑millimetres of substrate, indicating a localized aggregation rather than a diffuse distribution.
Biosecurity Assessment
Mike Taylor, manager of the Aquatic Team at Biosecurity NZ, stated that Potamilla alba does not represent a biosecurity concern. He emphasized that the species is unlikely to be harmful, noting the lack of known pathogenic traits, invasive behaviours, or significant ecological impacts associated with this worm in other regions. Shanti Morgan echoed this sentiment, adding that the worms’ appearance and behaviour do not suggest they would outcompete native species or alter habitat structure in a detrimental way.
Distribution and Historical Context
Although Potamilla alba is recognized as a New Zealand marine worm, its recorded distribution has been sparse. The 1951 Banks Peninsula sighting remains the only verified historical reference before the Jackson Bay observation. The current find expands the known geographic range of the species to include the West Coast, suggesting either a previously overlooked population or a recent range expansion. The council’s biosecurity report highlights that the species’ presence in Jackson Bay is “the best estimate based on one taxonomist’s opinion,” underscoring the need for taxonomic confirmation before definitive conclusions about its range can be drawn.
Habitat and Behavior
According to the marine surveillance report compiled by the council, Potamilla alba is known to form dense clusters that can be readily dredged in quantity by fishing boats. This clustering behaviour likely explains why the worms were concentrated underneath the mooring structures at Jackson Bay wharf, where sediments and organic debris may provide suitable settlement substrates. The worms’ filter‑feeding gills enable them to extract plankton and suspended particles from the water column, a lifestyle typical of many sabellid polychaetes that thrive in sheltered, nutrient‑rich environments such as harbours and wharf pilings.
Pathways of Introduction
Emily Rutherford‑Jones speculated that the most plausible vector for the worm’s arrival at Jackson Bay is transport on ship anchors, hull fouling, or ballast water sediment. Given the species’ propensity to form compact aggregates, small clumps could easily adhere to submerged surfaces of vessels and be released when the ships anchor or undergo maintenance. Boats were identified as a “key risk pathway” for the introduction of the organism to the wharf, aligning with broader biosecurity concerns about marine invasive species hitchhiking on commercial and recreational craft.
Surveillance and Monitoring
The West Coast Regional Council’s ongoing marine surveillance program aims to detect early signs of non‑native or potentially harmful organisms in the region’s coastal waters. The Jackson Bay finding triggered a targeted follow‑up survey to assess the worm’s abundance, precisely map its distribution, and determine whether any changes in density occur over time. The council plans to maintain regular monitoring at the wharf and nearby sites, coordinating with Biosecurity NZ to ensure any shifts in the worm’s status are promptly identified and evaluated.
Implications for Management
While the current assessment deems Potamilla alba low risk, the discovery highlights the importance of vigilant marine biosecurity practices. Regular hull cleaning, proper ballast water management, and routine inspections of mooring structures can reduce the likelihood of unintentional species transfers. Should future research reveal that the worm exhibits invasive traits or begins to spread beyond its current localized hotspot, management strategies may need to adapt, potentially including physical removal, targeted treatment, or public outreach to vessel operators.
Conclusion
The tentative identification of Potamilla alba in Jackson Bay adds a new datum to the understanding of New Zealand’s marine polychaete diversity. Although the worms appear benign and are present in high local densities, the episode serves as a reminder of the dynamic nature of marine ecosystems and the continual need for robust surveillance, accurate taxonomic work, and proactive biosecurity measures. Ongoing collaboration between regional councils, national biosecurity agencies, and the maritime industry will be essential to safeguard the West Coast’s coastal habitats against both known and emerging marine threats.