It seems so unfair – rock snot and lake snot suddenly invading the South Island's cleanest water. And it is still an unfolding scientific mystery.

Why did these two very similar Northern Hemisphere organisms – river-living didymo (Didymosphenia geminata) and another lake-living algae, Lindavia intermedia – hit New Zealand at much the same time back in 2004?



And could it be that this pair of bio-intruders are then doing the same thing here – spewing out this excess mucilage, a sticky polysaccharide – simply because our mountain water is so pure it stresses them out?



Hah, replies Lincoln-based Landcare researcher, Dr Phil Novis, who is trying to round up government funding to study lake snot properly.



He shouldn't repeat it, but some water ecologists joke darkly that these pesky arrivals are nothing that a good dairy farm wouldn't sort out.



READ MORE:

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SUPPLIED/LANDCARE Lindavia intermedia up close: sticky strands between two cells can be seen under the microscope.

Yes, it could be that they bloom, suck up what little phosphorous nutrient there is in our Southern Alp-fed lakes and rivers, and then start producing the icky stuff that is a public nuisance fouling water intakes and choking stream-beds.



So the coastal waterways are being spoilt by agricultural intensification, but now the high country water is suffering too because of the opposite. Life just isn't fair, is it?



However, Novis says it goes to show how vulnerable the ecology of lakes like Wanaka and Wakatipu really is.



And as a scientist, it is what comes next that now worries him, especially if it is the less-heralded lake snot that gets out of hand.



BIOLOGICAL BASICS



First some basic biology. Didymo and lake snot are diatoms – microscopic algal cells that are distinctive because they encase themselves in often spectacularly architectural silica shells or frustules.



Using silicon as a glassy protective armour gives diatoms a unique evolutionary advantage. It is the reason they are the dominant photosynthetic organism in both salt and freshwater plankton.

Also, many diatoms produce snot. Or rather they have a "jelly pore", the rimoportula, though which they extrude polysaccharides – simple starchy sugar-chain molecules.

The material is usually functional. Didymo uses it in small amounts to attach itself to rocks in fast-flowing streams by a stalk. Free-floating planktonic diatoms can organise themselves into loose meshes.

SUPPLIED Didymo's runaway production of stalk material chokes a river bed.

But for some reason, usually at the end of a seasonal growing bloom, it can tip over into a runaway production of gelatinous gunk.



Didymo can end up like thick fatty lumps. Lindavia produces a jelly of strands that get snagged by fishing lines or bunched into a scummy foam by wave action.



"In the water, the cells are fairly dispersed. But they are sending out these threads. So you only notice them when you concentrate them some way. It all starts gathering up like a net," Novis says.



This is why another name for lake snot is lake snow. When it is really bad, as in Lake Wanaka, frothy white flocs appear on the surface.



Novis says lake snot has been reported in European lakes in the past. It has cropped up in Lake Youngs, a water supply reservoir near the US city of Seattle more recently.

It is not toxic, just a mess. In its native habitat, it is not a big deal, except for swimmers or the hydro-dams and water companies that have to spend money cleaning their intakes.

DIDYMO DOWNUNDER



So to New Zealand. Both didymo and Lindavia appear to have arrived in the country in 2004. Or at least that is when they began to make their presence felt.



Novis says we are getting into data-free territory now – largely informed speculation. But it is likely that this was a coincidence.



The species are commonplace enough throughout North America and Europe. With the surge in angling tourism, they could easily have come in on someone's damp waders or fishing tackle.



Didymo was the one that sparked the public panic after its slimy mats were first spotted in the Waiau River in Southland because it was already known to be an easily spread problem.

SUPPLIED/LANDCARE Water scientist Professor Ian Hawes helps with the collection of lake bed sediment.

No one could predict how fast it would grow under New Zealand conditions. And it soon showed up in many different rivers. Early fears were it could choke South Island waterways, then work its way through the North Island too.

Novis says didymo is still a concern. But at least in its snotty stage, it comes and goes. Affected streams can be clear the next year. "It's not been quite the doomsday scenario it might have been."

Lindavia was also first noted in 2004. Anglers in Lake Wanaka started complaining about a strange brown scum fouling their reels.



However, Novis says much less was made of this as no-one knew what the organism was. And while it was making a mess of Wanaka's water supply – blocking sprinklers and dish washer filters – it didn't seem to be spreading into other lakes.



Otago University zoologist Dr Marc Schallenberg finally picked up on it in 2008 through his PhD students doing lake research. He began to make some noise.



But Novis says it was only after he and a team did some lake sediment sampling in 2012, and found Lindavia well-established in Canterbury's Lake Coleridge, that the alarm bell really started to sound with the authorities.



The same sampling showed Lindavia was getting going in Queenstown's Lake Wakatipu. And record checking suggested Lake Benmore could have had its intake screens blocked by the organism in the early 2000s – an earlier unrecognised outbreak.



Novis says last summer, Environment Canterbury (ECan) did an even more complete survey of the South Island and found Lindavia now lurks in a large number of lakes. Only a few, like Lake Ohau, are an exception so far.



Clearly it is not good news if all the lakes could turn as bad as Wanaka, says Novis. So after having been relatively ignored for a time, lake snot is definitely a research priority.



INVADERS HERE TO STAY



The question is what exactly turns on the snot production in Lindavia? "Currently it's kind of like a puzzle where you can't even tell which bits are edges, which bits are sky," Novis confesses.



He, Schallenberg and others have been studying Lindavia on a shoestring budget so far.



Didymo did get a research push as a biosecurity scare. The National Institute of Water and Atmospheric Research (NIWA) was given a contract to identify the precise water conditions under which it goes into its polysaccharide overdrive.



Schallenberg had been hoping to win an $8 million grant from the Ministry of Business, Innovation and Employment (MBIE) Endeavour Fund for a general review of South Island lake health.

SUPPLIED/ADVENTURE WANAKA White flocs on the surface of Lake Wanaka are a sign of heavy infestation.

He felt it was time for a complete picture of all 12 of the great lakes from Fiordland's Lake Poteriteri to Lake Coleridge.

Novis says MBIE turned this application down in June. However, there is still hope for a lesser $1m Smart Ideas grant to just look at Lindavia.

"If it comes through, it will be the most interdisciplinary team I've been involved with. We've got analytical chemists, we've got ecologists, we've got people good at building electronics, we've got phycologists [algae specialists] like me."



Novis says some things have already been agreed. A Lindavia workshop was held last December by Otago Regional Council. It was concluded the organism is here to stay as there is no practical way of eliminating it.



Poisoning whole lakes with algaecides is of course out of the question, Novis says.



So what a research programme has to focus on is the ecological explanation for why Lindavia switches to snot production and what could be done to manage that.

JOSEPH JOHNSON/STUFF Novis is hoping for $1m grant to study the conditions under which lake snot is produced.

WHY THE SLIME?



With marine diatoms, there are some fancy evolutionary theories for why cells might produce sticky strings and aggregate into clumps.



One is that it is a response to predators. Novis says green algae has been shown to react to grazing by copepods – tiny planktonic crustaceans.



"The cells all join together and grow spines so they can't fit into the grazer's mouth." Plausibly, the gunk could be another kind of defence mechanism used by diatoms.



A more extreme hypothesis among marine scientists is that the diatoms clump to sink. As their seasonal bloom comes to an end, a sudden mass die-off would take their predators with them, leaving the surface water clear to recolonise the next year.



However, these kinds of adaptive explanations are hard to stack up, Novis says. More likely for didymo and Lindavia is that the jelly production is a sign of something going metabolically wrong.



He says one of the surprises of Lindavia is that it is probably not a surface-dwelling, hot-weather breeder – what you would expect with photosynthetic lake blooms.



American researchers culturing species from the same family have found Lindavia likely prefers to live in the deeper water of a lake. "So it would be a slower grower that is used to colder temperatures and lower light."



Hence the idea that it is instead the stress of summer water mixing – being brought near the warm and bright surface by wind and water turbulence – that might be the unusual thing going on in the New Zealand setting.

Novis says this is backed up by didymo. NIWA's Christchurch-based diatom expert, Dr Cathy Kilroy, did laboratory tests which showed didymo does not produce excess mucilage when it is actually thriving.

Instead, it looks to be when a bloom depletes the available phosphorous in a river that it switches to runaway stalk production – that gelatinous mat.

Novis says it seems didymo is being driven by its environment in a way it can't shut off.



Under the strong New Zealand sunshine, but lacking the critical nutrients needed to turn this radiant energy into cell growth, all the photosynthesis gets directed uselessly towards churning out carbohydrate muck.



"That is the best current theory." And he expects it will be the answer for Lindavia too.



Lindavia produces a different kind of polysaccharide. But when large numbers are forced up into Central Otago's bright sun in nutrient-limited water, cell production gets diverted down this rather pointless metabolic channel.



It is just a mistake of nature because, as an invader, Lindavia is not fully adapted to New Zealand conditions. As simple as that.



'IT SEEMS LOGICAL'



"It seems logical. It's certainly plausible. It fits with the very limited evidence we currently have. Yet it's also an almost data-free picture at the moment," Novis cautions.



That is why the MBIE funding is needed to check the hypothesis in the laboratory.



But, jumping ahead, what does it mean for hopes of control?



Could, for instance, Lake Wanaka's problems be cured by chucking a few handfuls of fertiliser into the water at the right times to get Lindavia's metabolism back on track?



Novis shudders. No, not the right way to think about it at all, he says. There has to be more going on than this idea our alpine lakes could be "too clean" in terms of nutrients.

Novis says Lindavia is believed to produce a particular polysaccharide, beta chitin – coincidentally like that insects use in their hard cuticle shells. "If it's proven that is the slimy stuff it is excreting, then that's nitrogenous."

The implication from there is that it is in fact a nutrient imbalance that is stimulating Lindavia. Novis says it could be the mix of too little phosphorous plus a slight environmental excess of nitrogen which fuels the over-production.

Dairy farming can't get the blame. "There is no dairy farming in the Wanaka catchment."

However, Novis says it is not hard to point to possible sources of terrestrial nitrate run-off. Look at all the new housing development around the southern lakes, all the gardens and golf courses using fertiliser.

The ecology of these pristine lakes may be far more sensitive than we realise, he says.

"At Lake Coleridge, some of the alluvial fans have been developed there quite recently – to the point where a Landcare ecologist, who has had a family bach there a long time, said he was expecting something to change in the lake. He just wasn't sure what it was going to be."

Again it is speculation. Too early to point fingers, Novis says. However, this is why research is needed to find out exactly what triggers the lake snot response in Lindavia.

And the real worry is the question of what might come next.

BACTERIA JACKPOT

Like didymo, Lindavia could be less of a snot-producing pest than first thought. If it is only under certain stress conditions that it happens – not a result of thriving growth – it becomes more of a self-limiting situation.

Novis says Lindavia has already appeared, then disappeared, in Lake Waikaremoana in central North Island. Or that is, Lindavia itself remains. It just hasn't repeated a snot attack recorded in 2008.

And while Wanaka may have an endemic issue – costing it in terms of recreation, tourism and upgrades to the town's filtration machinery – other lakes might well escape with a low level of occasional outbreaks.

But that is a hope. And Novis says water scientists also have to reckon with what could follow if these alpine lakes start getting an annual dump of tonnes of organic material they have never experienced before.

"You're going from what is basically a carbon desert to all of a sudden these rich carbon islands. Masses of them. A jackpot for the bacteria and other heterotrophic organisms. That's a major disruption to the traditional ecosystem."

So how is that going to play out? It could be something. It could be nothing. But for sure, it is a reason to be doing the basic science.

No room for mysteries, says Novis. New Zealand needs to understand the precise causes and consequences of lake snot.