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An aggressive pest

By Bron

Mediterranean fan worm – (sabellidae) Sabella spallanzanii
Written by Luke Lim

On the winter day of June, the 10th, a small number of students ventured to the Takapuna rock pools by the beach to conduct a survey on the life that was in a 1-meter by 1-meter square. Most of the juniors, two middle school students and a senior student set up shop and began searching. I was excited just to be there so I began searching thoroughly when I came across what appeared at the time as an oddly straight stick swaying in the water not floating away. I dismissed it and kept searching. When the marine biologist supervising us came to help and check what I had listed, she exclaimed that the odd stick was in fact a Mediterranean fan worm, an invasive species that harms ecosystems by outcompeting filter feeders for food.

So who found the worm? I did. Who am I? I am a senior student at A.G.E., Luke Lim. Anyway, what are they? And why do they have such a huge impact? Well, that’s what I hope to explore.

Let’s look into their reproduction before anything else. How do they multiply? Male Mediterranean fan worms release sperm into the water to be captured by females. The fertilisation process takes place inside the female worm's tube, where the egg is released. Mature female worms are able to produce more than 50,000 eggs during each spawning event. The spawning event occurs over a time of around autumn-winter and the females aren’t restricted to a single batch of eggs during this period of time. This reproductive process is influenced by environmental conditions, water temperature and light exposure respectively. The larvae drift in the water for up to 14 days. If these worms are damaged they are able to regenerate parts while the worm continues to function, much like the regenerative properties of axolotls. I believe this makes eradicating these worms not feasible simply due to the fact that it can’t be killed using physical means and has a large population. It suggests either a different physical way to kill it or use a chemical means instead.

What do they look like? Why are they a problem? Where do I look for them?
The worms themselves are tube dwellers, in tough, mucous tubes, coated with sand, mud and debris. The main head has feather-like tentacles on either side of the mouth part. These tentacles are called radioles and shape a crown, controlling both the feeding and respiratory functions. Their width can get up to 150mm. The tube can get to over 40 cm and have a leathery, flexible and muddy-looking. They pose problems for ecosystems if left unregulated as they outcompete filter feeders by altering water flow for suspended food. They’re also annoying because they stick to a wide range of surfaces varying environmental conditions. Its fast rate of growth, and its prolific breeding habits, make it particularly aggressive in its competition for food. It has no known predators in New Zealand and has high amounts of heavy metals in the crown which leads me to believe it might be a potential anti-predatory strategy. They’re generally found on the hull of pretty much any kind of boat due to their ability to stick to so many surfaces.

If you’re feeling adventurous, how about a trip to the rock pools? Look around hard sub-tidal structures and small buried fragments of shell or rock. If unsuccessful at first, they could be buried up to 10cm deep in soft substrates or anywhere in shallow subtidal areas in the depth range of 1 – 30m deep so don’t feel so bad.

What can we do to at least prevent such a tyranny?
If you own any kind of boat such as ferries, yacht, a regular old fishing boat, a rundown rowboat or a huge naval battleship, make sure to clean the hull regularly to the extent of having no more than a light slime layer. Apply thorough coatings of antifouling paint and keep it in good condition. Having a good look at your hull and clean out any fouling before you travel to a new region. Don’t forget to clean and dry any marine equipment before setting sail to the new region as well. Look carefully for marine life in compartments on your boat that hold water. Finally, check anchors, propellers and any other sort of equipment for tangled seaweeds.

You must notify the Northland Regional Council if you think you have seen this pest outside of Whangarei Harbour.

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