1. A heavenly looking island

Imagine an island... an island located in the Pacific Ocean, high volcanic peaks covered in luxuriant emerald green forests and a deep blue sky, pristine beaches surround this island, and a heavenly breeze blows all the time...

Sounds like Paradise, doesn't it?... In fact it is taken from a tourist brochure...So, for most visitors their stay will no doubt remind of it, but sadly there are residents that possibly will never have the chances again to enjoy the marvels of this island, as it is also witness to an ecological disaster: The mass extinction (in the wild by now) of a whole molluscan fauna.

We are talking in this article about islands as Tahiti and specially Moorea, but possibly soon it could be assigned to not just a few of the islands part of the Society Island's group, in the South Pacific Ocean. We have been focussing in the molluscan genus Partula as the more representative genus of snails found there, but no doubt as the ecological chains have been modified, diverse plants and many other animals are facing the same fate.

2. Partula's pace

Well, at sometime in the past after the formation of these islands, and after these were colonized by plants, some small snails found the shores of them, possibly coming on drift logs, or attached to bird's legs. These snails found a world where no predators were to be found, a place with a limitless quantity of food and no competition from other animals or species of snails.

These snails were the predecessors of the different species of Partula snails that were inhabiting the mountain and valley forests just a few decades back in time. Now, on islands as Moorea it is not possible to find these endemics in the wilderness anymore. And nobody knows about the actual situation of the Tahitian species.

These snails belonging to the family Partulidae (genuses Partula, Samoana, and Eua), are no doubt facing all the problems arised due to past and actual human actions on these island's ecology. Being around 120 species known to science, these molluscs are to be found also on other islands of the South West Pacific Ocean, from Belau and the Marianas to the Marquesas and Society Islands. On each island there has been a process of radiation of the original predecessors that found these islands into multiple related species, adapted each one to different restricted area of the island ecosystem. It seems that on these two islands (Moorea & Tahiti) the endemic molluscan faunas have suffered the most, due to loss of habitat, and specially to the introduction of foreign animals and plants.

3. What do we know about Partula?

During history these animals have attracted the interests of not just a few scientists, Garret was one of the pioneers to discover to science the diversity of this group, and his works began the interests for these snails as a model in evolutionary biology. Later, Crampton made also a deep survey on these and other islands of the area trying to go deeper finding out the variation ratio to be encountered between the different species or inside each one of the species; until today and after generations of scholars, it can be sais it is one of the best known groups of snails of the world, in the field of genetics and evolutionary biology everyone has dealed with them... but it is just sad that all this knowledge has not been of much help during their dissapearance from their original homes.

Please have a look at this imageplate showing

some of these species from old collection.

The ones studying the behaviour of these snails noticed their arboreal habits, just a few are ground dwellers, most to be found on tree trunks and leaves from just a feet to several above ground. Being herbivorous, they seem not having specialized in a certain food source, decaying plant material, fungi, etc.. are all suitables for them.

These Partula snails belong to the pulmonates, snails with lungs for breathing, and are hermaphrodites, this is male and female at the same time, being a curious thing to know that they were found to be ovoviviparous, this is they may lay clutches of eggs (1-5), or give birth to young (at the same ratio), happening this at about fortnightly intervals (in the smaller species) or monthly intervals (in the larger species). Their average normal life-span is recorded around 5 years up to the species considered.

Nocturnal animals as they are, are known of being found feeding and mating during the night, with the first rays of sun they use to hide away attaching themselves to the underside of leaves or to tree trunks until the next night.

Morfologically their shells are conical, and medium sized, most times there is a large degree of variation to be found in the pattern that the shell shows in every colony/species. The usual shell colours are pale brown/dark brown tones not being found bright colours as in other related families

4. What happened?

It is a sad story this one, a story of foolish human behaviour, a story that ended with an entire molluscan fauna in JUST 10 years!... how it is possible?... Read and learn...

The local human population lived during generations on the island of Moorea in harmony with the surrounding nature, fishing and low scale agriculture were the main source of incomes for these islanders. In the 60's a farmer found a new way for making money, producing comercially Giant African snails Achatina fulica (Bowdich, 1822) for locals to eat. This same man found soon some economical difficulties and closed the farm to release into the wild all the foreign snails. This was the begining of the Achatina invasion of the island. Local farmers in the 70's began to find their crops eaten by the alien species, and for getting rid of them another foreign snail was introduced for biological control, this time Euglandina rosea (Ferrusac, 1821), a carnivorous species that was thought to eat the former invaders, but.... these were too large for them and began preying upon the smaller local endemics, all these Partula species. So the numbers Achatinas and Euglandinas grew alarmingly and the tiny local species began to find their way towards the edge of extinction.

5. The rescue from the edge of extinction

Luckily groups of scientists noticed the on going process of extinction taking place on the island of Moorea. In 1981 institutions as the Jersey Wildlife Preservation Trust began to find out the ways for saving these threatened species, and managed to get specimens of all the species for breeding them in captivity and stabilishing colonies in different zoos of different countries for not being responsible for the death of a whole species in case of possible diseases.

Today, we can still be honoured to have many of these species alive, although it is not possible anymore to find a wild Partula on Moorea island, there are different colonies at different institutions around the world, it is possible to see the largest single Partula taeniata colony on Jersey Island, at their captive breeding centre at Les Augres Manor. Also in the London Zoo they are helping to save many species.

And all this is made in the hope that someday, Moorea would be a Euglandina and Achatina free island, again a home for these species. There have been reports on recent reintroductions to certain areas of these captive bred Partulas, special areas where predators have been killed and are safe for making a living. These are their first steps back from the edge.

So, no doubt the only way for dealing in the future is thinking twice and learning from the past mistakes; introducing foreign species is the first cause of extinction on tropical islands, and these are not just the only ones where it has happened, Hawaii Islands, Guam, Mauritius, etc... are just other samples, nor are these snails the only animals affected, anykind of plant or animal is threatened because of this reason. And it is not a problem of the past to be solved, biological control is taking place even today.

For the general public it may be not a subject of concern, one or two snails less on the planet, but it really affects all the ecological balance, the food chains ... other species will in the near future suffer for the loss of the other ones, includying the humans!. Anytime heard about the "Domino Effect"?.

6. Related Websites

ANIMAL CONSERVATION

In 1994 an international expedition to Polynesia was arranged to create the first snail wildlife reserve. The site gives more info and adds the possiblity to adopt a Partula snail, this is, supporting their work with your funds.

JERSEY WILDLIFE PRESERVATION TRUST

Several colonies of partula are under their care, you can receive more info and also support their work being member of the trust or with donations to their several captive breeding projects (includying Partula).

DEPARTMENT OF GENETICS, UNIVERSITY OF NOTTINGHAM

Know more of Evolutionary and population genetics of land snails dealing with the different Partula species, the variability found inside each species and between all.

7. Further reading

Evolution and extinction of Partulidae, endemic Pacific island land snails. Robert H.Cowie. Bishop Museum Press.

New species of Land Snails of the Genus Partula from Raiatea, Society Islands. Henry Crampton. American Museum Novitates. Nº:1761 March 8, 1956

New and significant species of Partula from Moorea, Society Islands. Henry Crampton. The Nautilus Vol.XXXVII, April, 1924

Studies on the variation, distribution, and evolution of the Genus Partula. Henry Crampton. The Carnegie Institution of Washington. May, 1932

[Go Back to Journal of Malakos.com] [Go Back to Main Hall of Malakos.com]

©Copyright2000