Investigation of the Factors Affecting the Population Dynamics of Captive Partula Snails

Abstract

Partula snails, also known as Polynesian tree snails, were first recorded scientifically from Captain Cook's voyage 236 years ago. They are small gastropod molluscs which belong to the order Stylommatophora. Their distribution is focused in the Pacific region where the majority of the species are island endemics. Half the species are found in the Society Islands of French Polynesia where most research has been carried out. Wild populations were almost annihilated following the introduction of a predatory snail, Euglandina rosea, to control the introduced giant African land snail (Lissachatina fulica) which had become an agricultural pest affecting the local economy. In 1987 the Partula Propagation Group (PPG) initiated a worldwide captive breeding programme for Partula snails in an attempt to save them from extinction. In captivity, though, episodes of high mortality have led to the extinction of some species. The causes of these declines are as yet uncertain. This study aimed to investigate the factors that have affected the survival of 15 species (including two subspecies) of Partula snails in captivity. In summary, the results indicate that both environmental factors (temperature, relative humidity and light) and diet (calcium concentration and dog and cat vitamins in the diet) significantly affect the population dynamics of Partula snails. Both excess light and unstable temperatures and humidity had detrimental impacts on the survival and reproductive success of the species. Additionaly, the low concentration of calcium and the addition of dog and cat vitamins in the diet are also significantly detrimental on the survival and reproductive success of Partula gibba. These studies are highly significant because the biology and requirements of Partula snails are poorly understood, and this can jeopardise a successful captive breeding programme and future reintroductions into their natural environment. It is imperative that the factors that have affected the survival rates of snails in captivity for the last 25 years are fully understood. Partula snails face an uncertain future, with the mass mortality episodes observed during the years several species were lost. It is hoped that these findings stimulate further research in this area and can be applied to other species in similar circumstances.