It’s a darkish, wet night time within the beech forests of New Zealand. Because the rain patters on the leaf litter, a slow-motion chase performs out on the forest ground. A predatory snail is on the hunt. The dimensions of a lemon, it slides alongside the forest ground, leaving a glistening slime path in its wake. It’s prey: an unsuspecting earthworm, wriggling alongside the snail’s path.
A pause, and the snail lunches ahead, greedy the worm in its mouth and slurping it down like a protracted, saucy strand of spaghetti. This snail is a powelliphanta, a improbable New Zealand endemic that few have ever seen.
“These snails are fairly particular as a result of they’re carnivorous,” says Ruth Bollongino, pulling out a big plastic tupperware rattling with shells. “They’re not after the lettuce in your backyard. They’re out searching worms and different snails, and so they can suck down earthworms like spaghetti.” (Quick ahead to 1:50 within the video under to look at a powelliphanta predate an earthworm.)
Bollongino is the Science Advisor & Director of Operations for Undertaking Janszoon, a conservation group devoted to restoring wildlife and ecosystems inside Abel Tasman Nationwide Park. Located on the prime of New Zealand’s South Island, the park is known for its multi-day trek throughout a distant shoreline of bays and seashores.
Bollongino and I are sitting on the ranger’s hut at Anchorage campsite, the place I’ve traveled within the hope of seeing a flock of kaka, a garrulous and charismatic parrot species lately reintroduced into the park. However excessive within the hills behind us, removed from the vacationers and trekkers having fun with the seaside, are two species of endangered powelliphanta snail.
Bollongino rummages by way of the field and pulls out the most important of the shells. There are a minimum of 20 species within the Powelliphanta genus (with almost 60 subspecies) that reside throughout the North and South islands. Most are remoted populations dwelling in a small geographic space; on prime of a mountain, or in a selected patch of remnant forest.
This shell belongs to Powelliphanta hochstetteri. At almost 7 centimeters (3 inches) throughout, it’s the dimensions of a spherical, plump lemon, with a swirl of chocolate and caramel stripes. “And this isn’t even the most important species,” Bollongino says. “There are some that develop as much as 9 centimeters (3.5 inches). They’re actually, actually stunning.” Scientists suppose that some powelliphanta species can reside for about 20 years. The smaller shells in her assortment belong to Rhytida oconneri, a associated species discovered solely in Abel Tasman.
Rats, Snails, and Ravenous Rails
Powelliphanta had been as soon as so widespread that they prompted issues for drivers on wet nights, forcing them to swerve throughout roads coated with slow-moving snails. At present, they’re one of many world’s most endangered invertebrates.
Populations of most species are in decline because of a number of threats, together with invasive predators, habitat loss, and local weather change. At present, the highest of the South Island — together with Abel Tasman and the hills and forests surrounding town of Nelson — is likely one of the snail’s final strongholds.
A lot of Undertaking Janszoon’s work revolves round controlling invasive predators, like rats and stoats, to assist restore populations of native birds. The hope was that these efforts would additionally profit powelliphanta. However, as all the time in science, it pays to verify your assumptions.
In 2016, ecologist Brian Lloyd began a mark-recapture research at two plots excessive within the hills, within the west of the nationwide park. Yr after yr, Bollongino and her staff returned to the websites, selecting up each snail they might discover and tagging them with small, coloured numbers designed for shellfish and bee analysis. The tags allowed them to establish particular person snails and observe their destiny over time.
“So that is my little steampunk snail,” says Bollongino, selecting up one other giant shell with a tiny transmitter glued on. “We had 10 of those and we adopted their actions for a month to see how far they really go.” The snails adopted a random sample, trundling by way of the forest and even up bushes, however sticking inside the similar 5 or so sq. meters. “It’s not probably the most thrilling knowledge,” she says, laughing.
You may suppose that snails make for a straightforward research species. In any case, they transfer slowly and don’t chew. However powelliphanta analysis is grueling in its personal manner. The snails reside on the prime of steep, forested mountains, and so they solely come out on moist, wet nights. Which implies working 15-hour shifts within the chilly and the darkish, moist and shivering whereas utilizing headlamps to navigate the forest.
“It’s the toughest factor I ever did,” says Bollongino. “However however, it was additionally probably the most fascinating venture I ever labored on, since you study a lot. They usually all the time stunned us.”
One shock — and a vital piece of knowledge for conservationists — got here after Bollongino and her staff examined the shells of lifeless snails they discovered throughout their research plots. “Snails are nice research animals, as a result of even when the snail is lifeless, you continue to have the shell that provides you an thought of how they died,” she explains.
“So this one has clearly been eaten by a rat,” says Bollongino, selecting up a shell with a gap gnawed by way of the facet. “So that you see all of the little enamel marks right here, these zigzags, they do what I name a nibble frenzy. They only go nuts.”
Then she selects one other broken shell, with clear, damaged edges. This harm is brought on by weka — a big, flightless chicken associated to rails — which stalk by way of the undergrowth and fill the identical ecological area of interest as small mammals. Weka predation appears to be like distinctly completely different to rat nibbling, as a result of the birds kill the snail by positioning it on the forest ground after which smashing their sharp beak straight by way of the shell, creating clear breaks and deep punctures.
Bollongino and her staff discovered lots of upon lots of of weka-damaged shells of their research plots, permitting them to find out that the snails had been struggling a minimum of a 70% mortality fee from weka predation. Beneath that quantity of stress, they predicted that the native snail inhabitants would go extinct inside 4 to five years.
It was an necessary discovery as a result of till that time scientists assumed that invasive rats had been probably the most vital predators of powelliphanta, and that rat management was key to the snail’s survival.
Tiny Fences For Large Snails
Weka, like powelliphanta, are endemic to New Zealand. So why are they inflicting such issues for the snails? Bollongino explains a confluence of things is contributing to a growth in native weka populations.
Populations of lots of New Zealand’s native birds have collapsed because of invasive predators. Meaning much less competitors and extra prey for weka, who may also eat mice and rats. In the meantime, the weka have few predators to fret about. Because the extinction of the Eyles’s harrier and laughing owl, their solely actual predators are feral stoats, which is able to eat weka chicks and their eggs. The birds additionally reproduce shortly, with females able to elevating 4 or 5 clutches per season, including as much as 15 or so chicks.
“Within the 90s, they had been no weka right here,” says Bollongino. “They had been almost extinct within the space, and so they had been so treasured we’d report each sighting.” Now, the nationwide park campgrounds are plastered with indicators warning guests to zip up their tents and safe any meals, lest the gangs of inquisitive and protracted weka roaming the campgrounds snatch somebody’s lunch.
The resurgence of weka is a conservation success. However as a result of ecology is rarely easy, that comeback has come at a value for the snails. “What we see is that the decline of the powelliphanta coincides precisely with the arrival of weka information up within the uplands,” says Bollongino. “And we even have the shells that show it.”
The opposite downside is that the weka are simply certainly one of many threats the snails are up towards. Powelliphanta are additionally eaten by unique predators, together with rats, European thrush, hedgehogs, pigs, and Australian brush-tailed possums.
On prime of that, their habitat is altering. Those self same invasive species, together with goats and deer, are additionally consuming the forest’s understory to inside an inch of its life, inflicting soils to dry out and reducing the quantity of leaf litter the place the snails can cover and forage, and probably impacting their prey species.
“They’re simply being hammered from all sides, to not point out the impact of world warming,” says Bollingino. Final yr, the area skilled a extreme drought, with hardly any rain for 9 months. “The older snails can take care of it to some extent, however drought can kill the younger snails, like these little infants,” she says, holding up some blackberry-sized shells. “In order that’s the issue for the snails, the whole lot’s towards them. And with weka, it’s the opposite manner round.”
To assist powelliphanta inside the nationwide park, Undertaking Janszoon constructed two weka-proof enclosures in areas with surviving snail populations. These snail sanctuaries are 70 by 70 meters in dimension, with mesh that’s sufficiently small to maintain weka out, however giant sufficient to permit juvenile snails to disperse exterior of the fence.
Two years later, populations of each snail species are recovering inside the fence, and so are different invertebrate species. “There’s weta in all places, and earthworms and flatworms… it’s simply crawling with life, whereas exterior the fence, there’s simply nothing,” says Bollingino.
Bollongino says that the snails are an ideal reminder of why checking our assumptions with monitoring is so necessary for conservation. “We thought we simply wanted to regulate the unique pests, after which the whole lot would fall into place,” she says. “That’s typically the case, however not all the time.”
With out sound science, Abel Tasman’s powelliphanta may need been misplaced to weka overpredation. Now, Undertaking Janszoon and their companions on the Division of Conservation will be capable to guarantee these bizarre, great, earthworm-slurping megasnails survive for years to return.
Undertaking Janszoon is a part of the Kotahitanga mō te Taiao Alliance, a collaboration of Iwi (Māori Indigenous tribes), non-profits, and governments on the prime of New Zealand’s South Island. It goals to revive and improve nature throughout 3.4 million hectares of land and sea. The Nature Conservancy helps the alliance by offering facilitation, funding, science, and world experience.
