Wildlife

Manus Green Tree Snail

The Manus green tree snail (Papustyla pulcherrima) is found only on Manus Island, a 100 km long, densely forested island to the north of Papua New Guinea. The Manus green tree snail is an icon of the island and is heavily featured in the ceremonial dress of Manusians, appears on the provincial flag, and is often sold as jewellery. The shell is conical, emerald green in colour with a fine yellow border, and a white lip. It grows ~4 cm in total length and is internationally renowned for its beauty. 

While most conservation attention is focused on large charismatic vertebrates, invertebrates globally receive little if any attention ‒ and the Manus green tree snail is no different. Given that invertebrates (animals without backbones like insects, molluscs, and spiders) receive little or no funding WCS PNG has been pioneering a the use of a low cost technique known as “Wisdom-of- Crowds” to help understand the plight of lesser known species like the Manus green tree snail.

“Wisdom-of- Crowds” is a phenomenon seen when a large number of people, all acting independently of each other, can collectively estimate values with surprising accuracy. Many researchers have suggested this form of knowledge could be used to answer fundamental questions regarding natural resources in data-poor situations. By virtue of Manus’s widespread indigenous population living in and around the forest there exists a vast library of local ecological knowledge residing within the everyday population. We decided to tap this knowledge by interviewing over 400 Manusians and mathematically aggregating their knowledge about the Manus green tree snail. In this way we were able to construct an abundance map for the island, and could see snail numbers were declining over time.

As a result of this outcome we were able to get the Manus green tree snail assigned an IUCN threat classification of ‘Near Threatened’. In this process we identified two main risks: habitat destruction and over collection for shells. Large-scale habitat destruction caused by logging appears to be the greatest threat by far, with the expected loss of the snails being directly proportional to the amount of forest removed. Our study also identified that the Great Central Forest is a stronghold for the snails. Once again the ecological value of this forest has been emphasised, and importance of the partnership between WCS PNG and local community initiatives in safeguarding the forest cannot be underestimated.