What does it look like?
Mediterranean fanworm is a large, tube-dwelling worm. It is the largest fanworm in New Zealand with its body measuring up to 20mm wide and 800mm long. It has a prominent crown of feeding tentacles that extend out of the tube and can be 150mm wide. The crown is often banded orange, purple or white. The tubes are leathery, flexible and muddy-looking and are generally found on hard sub-tidal structures, but can also be buried up to 10cm deep in soft substrates.
Mediterranean fanworm can live in most artificial and natural habitats in the marine environment but it will not tolerate freshwater. It prefers sheltered, nutrient-enriched waters and is generally found in shallow subtidal areas in depths from 1 to 30m. It attaches to a range of solid surfaces including artificial materials (rocks, concrete, wood, steel), and benthic organisms (ascidians, mussels, oysters). It is also a common fouling species on moored vessels including car ferries, fishing boats and pleasure craft. It can also be found on soft substrates, generally attached to a small buried fragment of shell or rock.
Why is it a problem?
Mediterranean fanworm can form dense beds that are likely to out-compete other species and interfere with biological processes. Specifically, it has the potential to compete with native filter-feeding organisms for food and space, and in high densities is likely to impact commercially important species (mussels, oysters, scallops, etc). Mediterranean fanworm will readily settle on mussel grow-out lines and may reduce mussel growth by altering water flow around the lines and competing with mussels for suspended food (CSIRO 2001).
The ability of the species to attach to a wide range of surfaces in varying environmental conditions, its fast rate of growth, and its prolific breeding habits, make it particularly competitive. It has no known predators in New Zealand, and has particularly high concentrations of heavy metals in the branchial crown which has been suggested to be an anti-predatory strategy (Fattorini et al. 2004, in NIMPIS 2002).
Male Mediterranean fanworm release sperm into the water to be captured by the females. Fertilisation takes place inside the worm's tube, where the egg is released. Mature female worms can produce more than 50,000 eggs during each spawning event. Spawning occurs over a prolonged autumn-winter period and a female may release multiple batches of eggs. The reproductive cycles are influenced by local environmental conditions, particularly water temperature and light exposure. Larvae may drift in the water column for up to 14 days. If worms are damaged they are are able to regenerate parts while the worm continues to function.
You must notify the Northland Regional Council if you think you have seen this pest outside of Whangarei Harbour.
You can help prevent the spread of marine pests by:
• Regularly cleaning your boat’s hull – ideally keep fouling growth to no more than a light slime layer.
• Applying good thorough coatings of antifouling paint and keep it in good condition
• Ensuring your hull is clean and free of fouling before you go travel to a new region
• Cleaning and drying any marine equipment (e.g. ropes, lines, pots) before using in a new location.
• Inspecting areas on your boat that retain water in case they’re harbouring marine life.
• Checking anchors, trailers and other equipment for tangled weeds.