Haul a berth line up out of the water in February and you get a fair sample of what is going on down there: a sleeve of weed, a few firm lumps, maybe something that looks like a wet feather duster. Most of it is ordinary harbour life. Some of it is not from here at all, and the marina is precisely where it wants to be.
Why a Marina Is Exactly Where They Want to Be
Still Water, Hard Surfaces, No Scour
From a fouling organism’s point of view a marina is close to ideal habitat. The breakwater takes the swell out so nothing gets scoured, and the piles, pontoons, chains and hulls add thousands of square metres of hard vertical surface to a harbour that is otherwise mud and sand.
Add shade under the pontoons, a bit of nutrient run-off off the catchment, and water warmer than the open harbour on a still day, and you have a nursery.
Native species like it too, which is why there is green fuzz on your rudder by Christmas. The newcomers just do better, because whatever would eat them or crowd them out back home is not here.
Every Hull Is a Ferry
Marine pests do not cross open water on their own. Fanworm larvae drift for a matter of weeks at most, and a paddle crab is not walking across the Hauraki Gulf. What moves them the distance is us.
A boat that sits in one marina for a season, grows a decent beard and then motors somewhere else has done in two days what the organism could never manage alone. Sea chests, thruster tunnels, anchor wells, the trailing edge of a rudder – anywhere growth rides out a passage that would scrub a flat hull clean.
Then it settles and spawns, and the new marina becomes the next departure point. That is why a marina is a beachhead rather than a destination.
The Fanworm You Cannot Unsee
What Sabella Actually Looks Like Down There
Mediterranean fanworm, Sabella spallanzanii, is the one most berth holders can name, and the easiest to pick once you have seen one. The animal lives in a leathery grey-brown tube, flexible, not unlike a length of old hose, glued to whatever it settled on.
Out of the top comes the fan – a spiral crown of fine filaments, often orange or cream and sometimes banded, which opens to filter feed and snaps back into the tube the moment a shadow crosses it.
Full-grown ones run to a good arm’s length. On a still day with the light behind you it is possible to watch them from the pontoon, which is how plenty of people first realise their marina has them. They are genuinely handsome. That does not help.
How One Becomes a Thicket
One fanworm is a curiosity. They do not stay at one. Sabella spawns prolifically and the larvae settle on whatever hard surface is nearby, so a colonised pile goes from scattered tubes to a dense stand inside a couple of seasons.
At that density it is competing directly for what is in the water column – the same plankton that mussels, scallops and native filter feeders live on. It also turns bare pile into a soft forest that traps silt and shelters things that were not there before.
For anyone with a mussel farm nearby that is not an aesthetic problem, and it is why fanworm gets the attention it does.
Where It Has Got To
Auckland is where it took hold, and the Waitemata is still where it is most obvious. Since then it has turned up in other ports and marinas around the country, and the pattern follows where boats go rather than any natural current.
That picture changes by region, so it pays to check the current status with Biosecurity New Zealand or your regional council rather than what somebody told you at the fuel wharf three summers ago. Some regions run marine pathway rules and active response work, others are mostly watching.
Every new location arrived on something floating.
The Rest of the Under-Berth Crowd
Clubbed Tunicate, the Leathery Sock
Styela clava is less photogenic and much easier to miss. It is a sea squirt – a solitary one, not the jelly-like colonial sheets that coat pontoon floats – and it looks like a wrinkled leathery club, or a small brown sock standing on end on a short stalk.
They turn up in clusters on ropes, chains, floats and the underside of pontoons, and once a few hundred are on a set of mooring lines the extra weight is obvious. Most of us meet the clubbed tunicate hauling a line rather than diving.
They compete with the same filter feeders the fanworm does, and they are content in murky, warm, sheltered water a lot of natives find marginal.
The Paddle Crab With a Temper
Charybdis japonica turns up in a set pot or on the end of a hand line more often than under the boat. It is a solid crab with a broad shell, a row of spines along each side of the eye, and back legs flattened into paddles. It is bad tempered and will have a finger off you given half a chance.
Unlike the fanworm and the sea squirts it spreads under its own steam once it is inside a harbour, though hull fouling and ballast water explain how it got between harbours to begin with. It eats shellfish and competes with native paddle crabs and juvenile snapper.
If you catch one, do not put it back.
Undaria, the Winter Crop
Undaria pinnatifida is the odd one out – a seaweed, and common enough through parts of the country now that people have stopped noticing it. Golden-brown kelp, with a distinctly ruffled frill low on the stem, growing hard through the cooler months.
Which is exactly when most of us stop looking at the hull. It sets on pontoon floats, chains, piles and the boot top of anything sitting still, and a berth that was clear in April can carry a metre of it by August.
Winter is not the off season for fouling in a New Zealand marina. It is just a different crop.
What the Divers Are Looking For
Surveillance Starts at the Pontoon
Regional councils and Biosecurity New Zealand both run marine surveillance, and they start at the marina for the same reason the pests do – that is where the hard surfaces and the visiting hulls are.
Divers work the piles, the pontoon floats, the mooring chains and the pile wraps, and they look at the boats as well: hulls, running gear, and the niches where growth survives a clean. Some of that is a slow visual swim with a slate, some is a targeted check after somebody reported something odd.
Marina staff feed in too, because people who walk the pontoons daily notice change faster than anyone visiting quarterly. The point is not enforcement. It is knowing what is here and whether it is somewhere it was not last year.
The Places They Check First
Ask a surveillance diver where they head first and the list barely varies: the shaded underside of pontoons, the inside faces of piles, chain and rope in the top few metres, and anything sitting undisturbed – a dinghy on a swing mooring, a boat with a flat battery and no antifoul left on it.
On vessels the interest is in the niches rather than the flat panels:
– sea chests and their gratings
– thruster tunnels and prop shafts
– anodes, rope cutters and transducer housings
– the trailing edges of rudders and keels
That is where growth hangs on through a passage. None of it surprises anyone who has cleaned their own boat. The difference is that the divers catalogue it rather than scrape it off.
What a Berth Holder Notices First
Reading Your Own Hull and Lines
You do not need a dive ticket for any of this. Most first sightings come from berth holders doing ordinary jobs – pulling up a fender line, checking an anode, running a hand along the boot top, looking down off the pontoon on a still morning.
What earns a second look: a tube that feels leathery rather than shelly, a fan that snaps shut when you move over it, firm knobbly clusters on rope that were not there last month, or frilly brown kelp on a chain in the middle of winter.
Photograph anything you are unsure about, with a hand or a shackle in frame for scale. A photo beats a description, and it means the next question gets answered by somebody who does this for a living.
Who to Ring, and What Not to Do
Suspected marine pests go to the Biosecurity New Zealand pest and disease hotline, and your regional council will want to know as well – they run the local response and can tell you the current status in your patch. Marina management is worth telling too; they usually know before the paperwork does.
What not to do is scrape it off at the berth. Fanworm fragments and sea squirt clusters dropped into still marina water are a spawning opportunity, not a disposal method.
Lifting the boat, cleaning on the hardstand and capturing the waste is more hassle and more money. It is also the only version that does not move the problem three metres to the left.
None of this is a reason to stop looking under the boat. Berth holders are how a lot of these populations get found in the first place, and people who never look are how they get established quietly. The fanworm on the pile is a beautiful animal and it does not belong here, and both of those things can be true while you are reaching for your phone.
3 Comments
The bit about winter being a different crop is spot on. Hauled ours end of July expecting a reasonably clean bottom and there was undaria hanging off the trailing edge of the rudder like a lettuce. Never used to bother looking that time of year.
Same story here Toby, though ours was worse on the mooring chain than the hull. The chain is the bit everyone forgets about.
Question on the photograph advice – does the council want the shot before you touch anything, or is it fine to lift the line clear of the water to get a decent look? I am fairly sure we have clubbed tunicates on the bow line at the moment and I would rather not be the person who spread them by handling it the wrong way. Also good to see the fanworm described honestly, they really are a nice looking thing.