This situation was transformed in 2003 when the French Polynesian Government and a consortium of International Partulid Conservation Program institutions supported the preparation of a conservation and management strategy for the region’s endemic partulid and trochomophid snail fauna and its associated habitat. The resultant set of extensive field surveys has ascertained the status and location of the majority of surviving populations of endemic and pest species on the Society Islands group. There now exists the possibility of preventing any further partulid and trochomorphid species extinctions, and of re-establishing the 11 species that currently survive solely in the international breeding program.

Cause of Decline: The principal agent of extinction and rarity has been, and remains, introduction of the alien predator snail, Euglandina rosea. Although the damage wrought by this voracious predator has been disastrous, there is cause for hope as the last two years of survey investigations have confirmed that the predator is now relatively rare. This will give an opportunity for surviving populations to stabilize, and makes a cautious re-establishment program more feasible. LINKS: Bristol Zoo, England Partula Fact Sheet

A small (but mighty) part of forest ecology
The endemic land snails of French Polynesia form a significant and well-known component of the region’s biodiversity. They play a role in the ecology of the forests. Their extraordinary morphological variation has been the focus of classic studies in evolutionary and ecological genetics. These endemic snails are also part of Polynesia’s rich cultural heritage, most notably through the traditional production, at a sustainable rate, of shell jewellery (hei in Tahitian) by local artisans.

The family Partulidae consists of around 125 species attributed to three genera, Eua, Samoana and Partula. Partulids are endemic to many of the volcanic islands of the South Pacific, mostly in Polynesia, and consist of many species either extinct in the wild or threatened by human interference. They are one of three ancient, endemic land snail families of the inner Pacific, the others being the Achatinellidae and the Amastridae (endemic to the Hawaiian archipelago). Partulids have an enormous geographical range, from Belau, east of the Philippines, to the Marquesas Islands, 8500 km away to the west, yet there are only three genera throughout: Eua (four species) in Tonga and Samoa, Samoana (25 species) from east of Fiji to the Marquesas Islands, and Partula (100+ species) from Belau to the Austral Islands (see map below). The epicentre of their evolutionary radiation was in the Society Islands, where more than half of the recognised species were found, though their taxonomy has not been fully clarified.

Current status
Species in the family Partulidae were once widespread over the high islands of French Polynesia. Sadly, between the mid 1970s and mid 1990s an estimated 60 species (80% of the total of 75) have become extinct in the wild with a further 11 (15% of total) only surviving in the ex situ populations of the International Partulid Conservation Program. The cause of this major species loss was the carnivorous snail, Euglandina rosea, which was introduced to the region as a bio-control agent in a failed attempt to manage the garden pest, the giant African snail, Lissachatina fulica. As a result of invasion by E. rosea the distribution of many of the surviving partulid species have been rapidly reduced to small, isolated populations. The same is true of endemic species from the family Trochomorphidae. Currently no partulid species is listed as less than Vulnerable on the IUCN/WCMC Red List 2001, and around one third are Extinct. The extensive surveys conducted over 2004 and 2005 have revealed, however, that more populations on Tahiti, and to a lesser extent, Moorea, have survived than was believed but that many of these populations are in need of protective action, and that nowhere are they very common.

Past distribution
The French Polynesian Partula genera consisted of 58 species of single island endemics on six islands of the Society group. Often they were very common, with Polynesian artisans collecting shells (for the making of traditional hei) and researchers (genetics and evolutionary ecology) able to remove thousands of individuals without lasting effect on population dynamics. The genus Samoana consisted of around 15 species, some found on more than one island, spread over five of the Society Islands, six of the Marquesas Islands, and two of the Austral Islands. These species were not normally found in such densities as Partula. The rare genus Trochomorpha numbered just 5 species from five islands in the Society group, 2 of which were single island endemics.

Causes
Introduced predators: The principal agent of extinction and rarity has been, and remains, the alien predator snail, Euglandina rosea. Although the damage wrought by this voracious predator has been disastrous, there is cause for hope as the last two years of survey investigations have confirmed that the predator is now relatively rare. This will give an opportunity for surviving populations to stabilize, and makes a cautious re-establishment program more feasible.


It is unknown as yet whether or not the little fire ant, Wasmannia auropuncta, a disastrous recent invasive (identified in July 2004) will prove to be an additional threat. At the moment there is an attempt to control its spread from four urban locations on Tahiti. The New Guinea flatworm, Platydemus manokwari, has had a disastrous effect on snail fauna on some islands of the western Pacific. It may be present in the Society Islands and has been reported from the Marquesas Islands, although there have been no official introductions (to control Lissachatina fulica).

Habitat loss and alteration: Two species of Partula (P. clara and P. hyalina) and one of Samoana (S. attenuata) on Tahiti (also at high altitude and on Moorea) persist in lowland habitat disturbed by human activities and by invasive pest plant species), and one species of Partula (P. taeniata) on Moorea survives in similar habitat, in four small populations. At least two other species on Tahiti (P. otaheitana and P. affinis) and maybe one on Moorea (P. mirabilis) are confined to high altitude or remote areas, and loss of/damage to habitat is beginning to impinge on their distribution. Illegal forest clearance, forest clearance for housing and roads, the pointless clearing of trails for tourists, and even “wear and tear” by scientists, can all have a deleterious effect on these fragmented habitats.

Climate change: It seems that the Samoana species of the Marquesas Islands no longer persist in low/middle altitude areas and are confined to the high ridges. The islands have been occupied for over 1000 years and the human population was once much more widespread, so it does not appear to be increased human activity that has removed the Marquesan partulids from lower altitudes over the last few years. Sensitivity to environmental change often makes mollusks good bio-indicators. It is possible that a small rise in annual temperatures could push some species to higher altitudes, though difficult to investigate.

Small population size: The problems inherent in small population size are now among the major threats to the surviving partulid and trochomorphid populations. These include: loss of genetic variation; random events in the survival and reproduction of individuals; and increased susceptibility to environmental factors (e.g. changes in weather, food supply and the nature and numbers of competitors, predators and parasites).

Ecology and plans for the future
Most species are cross-fertilizing hermaphrodites, with self-fertilization relatively rare (though this method of reproduction tends to be more common among members of the genus Samoana). The overall rate of selfing of P. taeniata in the wild was estimated from allozyme studies to be only about 2%, though it could reach 20% in the first group of young (Murray and Clarke 1976). All species of partulid are ovoviviparous (giving birth to live young), 1-2 mm newborn growing to adulthood in as little as 3-6 months (Johnson et al. 1993). They are long-lived, 17 years having been recorded in captivity for
P. taeniata from Moorea.

Mark and recapture experiments have confirmed the hypothesis of very small neighborhoods of the Moorean species, at least - approximately 200 m2. Such extreme reluctance to disperse would appear to be at variance with the relatively recent colonization of their endemic islands. However, rapid range expansion can occur through the establishment of populations by rare long-distance movements (by passive dispersal in the case of Partula).

The Action Plan for this project summarizes the conservation situation to date and details the following key recommendations: Regular monitoring of individual populations and their habitats; identification of suitable sites for predator-proof reserves; the translocation of populations in immediate danger, where feasible; upgrading the protection status of key sites; curbing further introductions of predatory species through increased community awareness; expanding genetic, ecological and pathological research on both the endemic and pest species; and extending the ex situ culture of endemic species to their country and island of origin.

It is necessary to keep as many individual populations on Tahiti and Moorea under regular surveillance as is possible.

• Re-establishment
  The tested predator-proof reserve strategy remains the best medium to long-term protective measure against E. rosea, both for in situ populations of endemic snails in imminent danger and for the re-establishment of species lost from the wild. The continued assessment of suitable reserve locations is therefore a key action need.
• Translocation
  This is not a strategy that has been tested on snail species in French Polynesia, but it has not worked especially well elsewhere (Parrish et al. 1995). However, this may be a necessary conservation requirement where a population is immediately menaced and it is not practical to take other protection measures.
• Habitat protection
  Some 111 sites of ecological interest and conservation importance across all the islands of French Polynesia have been identified by scientists involved in the conservation of different taxa (Meyer et al 2005). A number of these (mainly high altitude) sites contain remnant populations of partulids. This site data will be used to promote the upgrading of protection status of these key sites.
• Education
  Community awareness achievements to date need to be built upon to maximize local understanding and support of the region’s endemic mollusk fauna and the importance of preventing further introductions of the two pest snail species and the New Guinea flatworm.

Woodland Park Zoo has participated in the Association of Zoos and Aquariums' Species Survival Plan for Partula since 2003, rearing a captive population of Partula nodosa. P. nodosa is listed as Extinct in the Wild by the IUCN Red List. For more information about this project, please contact the SSP Coordinator, Ric Brewer at ric.brewer@zoo.org

Supported since 2004