2017 Partula expedition
Partula tree snails and the Euglandina threat
Partula snails Partula conservation Euglandina

Partula 2017 research expedition

by Justin Gerlach

Download expedition report

Expedition diary

Expedition background:

For many years Partula snail conservation seemed like a hopeless task, with no prosect of eliminating their Euglandina predators and little hope of re-establishing the tree-snails in the wild. This has now changed, with experimental reintroductions of several species. Current evidence suggest that some of these may be successful, as long as predator populations remain low. We don't know what determines the occasional reappearance of the predators, and this is a point that needs urgent investigation.

In order to determine whether or not Partula can be re-established in the wild I investigated the ecology of the predators (Euglandina snails and Platydemus flatworm) and surveyed surviving wild Partula populations. Islands visited and species searched for were:

  • Tahiti - four species have been reported from high-altitude sites in the past 20 years: Partula compressa (overlooked since 1884 but a population was found in 1997), Partula cytherea (recent shells of a misidentified population were found in the 1990s), Partula jackieburchi (high-altitude populations may have been misidentified), Partula laevigata (overlooked since the 1840s, until a population was found in 1997 but misidentified until now), in addition to the monitored populations of Partula affinis, Partula clara, Partula hyalina, Partula otaheitana, Samoana attenuata, Samoana burchi, Samoana diaphana
  • Moorea - monitored populations of Partula taeniata, Samoana attenuata
  • Huahine - Samoana annectens was photographed from the top of the island in 1995
  • Raiatea - Partula meyeri was discovered on the highest peak of the island in 2006, Samoana attenuata was photographed twice
  • Tahaa - no reported survivors
  • Bora-Bora - no reported survivors
  • Maupiti - only reports are shells of an unidentified species

    My progress through the islands can be followed below and the expedition report downloaded:

    Day 1 - 2nd August

    Tahiti - Tiapa valley

    Arrival in the early morning. Morning accompanying Trevor Coote to his monitoring site for Partula incrassa, the only site for this species. Three were found, on introduced avocado trees. Some Achatina were present and no sign of flatworms although this was the first place Platydemus was seen (in 2006).

    Day 2 - 3rd August

    Tahiti - Mt Marau

    Exploration of the ravines off Mt Marau, with Trevor Coote, Eric Lenoble and Cindy Bick (visiting from Michigan to study Partula hyalina survival). The ravines explored were sites where Partula were known to survive. Good populations of P. otaheitana were found along with shells of Samoana burchi. A small number of other snail species were present, mostly remarkably coloured and shaped Succinea (another interesting island radiation). A flatworm (possibly Patydemus) was found in one site and shells of Euglandina at another, but neither appear to have established populations.

    Day 3 - 4th August


    Arrival on Maupiti, the most westerly of the Leeward islands. This is very different from Tahiti, very quiet and laid back. Maupiti has never been searched for Partula, simply because it is not supposed to have any. However, a few shells we found around a decade ago but have not been identified. Over the next few days I hope to find more and answer the questions - what are they, what were they doing here, why did they die out or are they still here? So far a quick search of the roadsides suggests that this is one of very few islands not to have been invaded by Lissachatina fulica.

    Day 4 - 5th August


    I admit to not having spent all my time searching for Partula. Even the most obsessive snail biologist finds swimming with manta rays irresistible. Tomorrow I will find out what lives above the cliffs.

    Day 5 - 6th August


    The only snails to be found were at the very top of the island. Euglandina was present but now seems to be extinct, perhaps because of the Platydemus flatworm that I found. I did find two shells of the mystery Partula. It looks like P. lutea of Bora Bora, but what was it doing on Maupiti? Perhaps a Maupiti endemic? Either way it is sadly extinct, with Euglandina the most likely culprit. Although not promising for conservation this was an important day scientifically.

    Day 6 - 7th August


    Today plans were thrown out by rain. It was to have been a day of travelling back to Tahiti but ended up being a wet day of waiting on the airstrip motu (coral cay on the barrier reef). Our flight diverted to nearby Bora Bora to wait in case the very short airstrip dried out, but finally the pilot decided it was too wet. Of course, by then it was the driest part of the day. We wait in hope of less rain tomorrow. Ironically there is plenty of room for a longer airstrip on the motu, if only it had been put the other way round.

    Day 7 - 8th August

    Maupiti to Tahiti

    A wet night but a dry day, so a return to Tahiti was possible. Tahiti looked far from welcoming under a thick blanket of dark cloud. However, apparently it has not rained here. Moorea looks even worse, I think I might be relieved that I am not spending the night watching flatworms as per the original plan.

    Day 8 - 9th August


    Magnificent Moorea! Not only stunning scenery but plenty of Partula. The only mangrove population of Partula: P. taeniata (left) and a juvenile P. tohiveana produced by the zoo adults reintroduced last year. So some Partula conservation works. On the other hand I found flatworms and a baby Euglandina, which gives me some very useful observations and more hypothese to test.

    Day 9 - 10th August


    It's back to the Leeward islands for the next island: Huahine. From now on, in the unlikely event of my finding any more Partula, they will be new discoveries. Today's event was a search along the beach crest for the site of Andrew Garrett's grave. Garrett disovered more species of Partula than anybody else and also noted their ecology, back in the 1860. American by birth, whaler, then shell collector and artist, he settled on Huahine and is buried here. His grave took a bit of finding, being totally engulphed by a thicket of Hibiscus tiliaceus trees. As this used to be a plant favoured by Partula I can hope that maybe one day there may be some Partula in the tree above him.

    Day 10 - 11th August

    Huahine - Mt Turi

    A highly successful ascent of the lower of two peaks of Mt. Turi, Huahine's highest mountain. Flatworms are abundant and in places the slope vegetation is a horrible tangle of Hibiscus stems and the smothering invasive creeper Merremia peltata. There is howevever some good habitat on the ridge. Even on the slopes there are things to find - there I found a shell of a Samoana, sister genus to Purtula. So the first rediscovery. Still some question over the identity at it doesn't look like the Huahine endemic S. annectens. Although I didn't manage to find any live ones I did find three shells, so they do still exist.

    Day 11 - 12th August

    Huahine - lowlands

    A walk around the larger part of the island (Huahine-Nui) turned up old shells of Achatina in some areas and fresh ones only in one agricultural site. There is no sign of Euglandina at all, other than the two very old shells I found yesterday. I also paid a visit to the sacred eels of Faie, enormous freshwater eels at least 1.5m long and a good 20cm in diameter. It has now settled in to rain, I wouldn't have been able to make it up the mountain today.

    Day 12 - 13th August

    Raiata - Temehani Ute Ute ascent

    The original plan had been to reach the summit of Raiatea, home of Partula meyeri, by helicopter. The helicopter company ceased operation in June so this was replaced by a plan to attempt the arduous climb. Howver, it proved impossible to organise the assitance and path cutting this would need. The third version was to climb the second highest peak, Temehani Ute Ute. The Temehani plateau is one of the exceptional places for biodiversity and I had found Partula on Temehani Rai in 1992. The higher Temehani Ute Ute has never been surveyed for snails. I made the climb with Jean-Yves Meyer, expert on all things botanical in Polynesia. We had an excellent day for the climb. Snailwise it was interesting but disappointing - no Partula and old shells of Euglandina.

    Day 13 - 14th August

    Raiatea - Temehani Ute Ute descent

    Light rain from midnight turned into pouring rain all day. A miserable start just got wetter and colder, with hardly any visibility in the cloud. This is why Temehani Ute Ute is a high altitude heath and bog. I don't think I've ever been as wet. The morning was spent searching for snails (me) and plants (Jean-Yves). It was a botanically successfu ltrip, but still no snails of note. The descent was horribly slippery and doesn't bear thinking about. It is interesting to have found that there are no flatworms along what was essentially a transect from sea level to 800m. This is in marked contrast to Faaroa bay where flatworms ate all the Partula released there last year.

    Day 14 - 15th August

    Raiatea - Uturoa

    A gloriously sunny day in Uturoa trying to work out whether the ferries to Tahaaa island bear any relation to the schedules on the internet (probably not), and looking for flatworms (not Platydemus but the unidentified species from Moorea). Uturoa has a new seafront since I was here 25 years ago, it was a one horse town then, and is barely more than that today.

    Day 15 - 16th August

    Raiatea - Hamoa

    Rain and strong winds prevented the day trip to Tahaa. Instead I made an earlier move to Hamoa valley. This was where I collected the last surviving Partula faba and Partula navigatoria 25 years ago. I felt rather excited to be revisiting the spot. It has changed radically, but more importantly is infested with astounding numbers of horrifying big, sticky, oozing Platydemus flatworms. I am going to have nightmares tonight.

    Day 16 - 17th August

    Raiatea & Tahaa

    I made it to Tahaa, with time for a quick survey of snails on the ridge at the centre of the island. Flatworms are not present, nor are Euglandina, but then neither are Partula. Tahaa is very quiet and very isolated. Uufortunately the forests are very degraded by a long agricultural history. Back on Raiatea in the afternoon I mapped the northern distribution of flatworms.

    Day 17 - 18th August

    Raiatea - Faaroa

    Partula were reintroduced to Faaroa valley in 2016, before it was known that flatworms had invaded the island. The flatworms ate all of the released snails. The aim of my visit to Faaroa was to investigate the flatworm situation, rather than in the hope of finding any notable snails. When I surveyed Faaroa in 1992 it was an area of small plantations and forest (mostly bamboo), littered with Partula shells in the aftermath of the Euglandina invasion. Today the agriculture is much more extensive and the Partula shells are long gone. Flatworms were common, but not on the same scale as at Hamoa. It appears that the flatworm invasion is a wave moving north.

    Day 18 - 19th August

    Bora Bora

    I have now moved to Bora Bora. This most dramatic of islands is the centre of tourism in the region. It has the most large hotels, the highest prices and the most development. However these are all concentrated on the motus and around the harbour. Most of the island is much less developed. Very few of the tourists here will be aware that the mountain above them has never been climbed. Partula are thought to have been driven to extinction here in around 1994 and there is little hope of any survival, but it's worth a look.

    Day 19 - 20th August

    Bora Bora

    This island turns out to be more interesting thatn I expected. True there are no live Partula, but strangely the ground is still littered with Partula shells, more than 20 years after their extinction. Can these shells really have been lying on the forest floor for that long? Euglandina also seems to have died out at much the same time. On the other hand there are flatworms here, the dreaded Platydemus but also the fantastical looking earthworm predator Bipalium kewense. Flatworms aren't common though and this island might have interesting reintroduction potential. Very strangely tiny arboreal tornatellinid snails are very common, species which I've not seen elsewhere, even in more appealing habitat

    Day 20 - 21st August

    final day

    Before starting the long series of flights back home there has been time for one last exploration of Bora Bora. The slopes just below the great cliffs of Mt. Otemanu are the typical Polynesian mid altitude forest of Hibiscus nd Inocarpus. As with yesterday I found old Partula, appearing older than those form yesterday. There was nothing new, but this does confimr the extinction of the island's Partula and the spread of flatworms across the island. Notably here there are new clearings for large houses up on the hillside. At least the habitat on and above those cliffs will remain safe.

    If you wish to support the continuation and further development of this project please donate below or contact Justin Gerlach