In a study by Sugiura (2009) the survival rate of P. manokwari decreased when animals were exposed to 10°C for more than 2 weeks. Kaneda et al. (1992, in Sugiura 2009), examining the developmental period of P. manokwari egg cocoons and juveniles, suggested that the developmental threshold of juvenile and cocoon stages was 11.7°C and 10.0°C, respectively. Therefore, 10°C may be a threshold temperature for the establishment of P. manokwari. Ambient temperature may regulate seasonal variations in predation pressure on land snails. In Japan, higher temperatures may have promoted increases in flatworm population density and feeding activity from early summer to autumn, resulting in the very high predation pressures on land snails observed in July, September, and November (Sugiura 2009). Recent global warming may increase the probability of invasion and population establishment, and elevate the impacts of P. manokwari in temperate regions (Sugiura 2009).
Sugiura and colleagues (2006) surveyed the presence/absence of land snails and P. manokwari in September to October 2005 and found land snails of introduced species (A. fulica, Acusta despecta, and Bradybaena similaris) surviving in coastal areas, probably because of the absence of P. manokwari. P. manokwari does not occur in the urban coastal area, perhaps because of environmental factors such as lack of adequate vegetation (S. Sugiura et al. pers. comm., in Sugiura et al. 2006).
Principal source: Barnes, 1968. de Beauchamp, 1963. Eldredge and Smith, 1994, 1995. Hopper and Smith, 1992. Muniappan, 1987, 1990. Muniappan et al., 1986.
Compiler: Dr. Robert H. Cowie, Center for Conservation Research and Training, University of Hawaii & IUCN/SSC Invasive Species Specialist Group (ISSG)
Review: Dr. Robert H. Cowie Center for Conservation Research and Training
Publication date: 2010-02-13
Recommended citation: Global Invasive Species Database (2024) Species profile: Platydemus manokwari. Downloaded from http://iucngisd.org/gisd/species.php?sc=133 on 08-12-2024.
Invertebrate species represent more than 99% of animal diversity; however, they receive much less publicity and attract disproportionately minor research effort relative to vertebrates (Ponder and Lunney 1999, in Lydeard et al. 2004). The global decline of nonmarine molluscs may be facilitated by the spread and introduction of predatory flatworms (Platyhelminthes: Turbellaria), in particular the flatworm P. manokwari. P. manokwari has been introduced into many locations for use as a biological control agent for the giant African land snail (Achatina fulica). It is an effective predator that poses a serious threat to native snails. Vulnerable native snails threatened by P. manokwari include endemic Partulidae in Guam (Hopper & Smith 1992) and Mandarina snails in the Ogasawara Islands (Japan) (Satoshi 2003).
It is estimated that there are about 4000 native oceanic Pacific island land snails (a number that excludes the continental islands of New Zealand and the island of New Guinea (Barker 1999, Cowie forthcoming, in Lydeard et al. 2004). These unique native snail faunas are disappearing rapidly (Bauman 1996, Cowie 2001a, Cowie and Robinson 2003, in Lydeard et al. 2004). Terrestrial molluscs have the highest number of documented extinctions of any major taxonomic group (Lydeard et al. 2004). Since the year 1500, 288 (40.2%) of the 717 recorded extinctions of animal species have been molluscs, and terrestrial species (land snails) constitute 68.1% of all mollusc extinctions (IUCN 2008). The Endodontidae, probably the most diverse Pacific island family (Solem 1976, in Lydeard et al. 2004), appear to be completely extinct or reduced to sparse remnant populations. All the Partulidae of Moorea (French Polynesia) are extinct in the wild (Murray et al. 1988, in Lydeard et al. 2004). In Hawaii, as many as 90% of the 750 recognised species of land snails are extinct. On Rota (Northern Marianas), 68% of the 43 species are extinct or declining, and in the Samoan archipelago, almost all are declining, although a smaller percentage is extinct (Cowie & Robinson 2003). These estimates suggest that overall perhaps 50% of the land snail fauna of the Pacific islands has disappeared recently.
Experts suggest that the continued introduction of alien predators such as P. manokwari should be strongly discouraged in order to conserve such unique island snail species (Cowie &d Robinson 2003). The introduction of P. manokwari is a serious concern in the conservation of the unique land snails of tropical islands (Sugiura et al. 2006). It has been considered a cause of the extinction of native land snails on several Pacific and Pacific Rim islands (Sugiura & Yamaura 2009). The endemic snail genus Mandarina (Okochi et al. 2004) is thought to have declined because of P. manokwari predation on Chichijima (Chiba 2003, Ohbayashi et al. 2005, in Sugiura et al. 2006). Biological control introductions pose a serious threat to endemic land snails because both E. rosea and P. manokwari feed on any species of live gastropods, including A. fulica (Kaneda et al. 1990, Hopper & Smith 1992, Civeyrel & Simberloff, 1996, Cowie 2001, Cowie & Robinson 2003, Ohbayashi et al. 2007, in Sugiura 2009).
Physical control: Hot water treatment to destroy pests has recently been used during the quarantine of ornamental plants. Sugiura (2008) examined the possibility of using hot water treatment for introduced soil animals in potted plants. The author designed an experiment to determine whether hot water treatment (immersion in water at 40°C, 43°C, 45°C, 47°C or 50°C for 5 min) kills soil animals, including the invasive alien terrestrial flatworm P. manokwari. The water temperature required to kill flatworms (=43°C) and earth-worms (=43°C) was lower than that to kill snails (=50°C) and ants (=47°C). Use of hot water for protection from alien soil animal invasions may mitigate their environmental impacts, particularly on oceanic islands where valuable biota could be threatened (Sugiura 2008).
Research and Knowledge: Future priorities in Mollusc Conservation include research (biotic surveys and taxonomic studies along with gathering of basic ecological and biological information) (Lydeard et al. 2004).
Education and Awareness: Information exchange should be improved via dissemination of information through the internet, keys, education etc. enabling greater worker base through training (Lydeard et al. 2004).
Integrated Management: Greater integration and coordination between management agencies, research institutions, and other stakeholders is essential (Lydeard et al. 2004). The resources that are currently available to manage global non-marine mollusc biodiversity are insufficient. Scientific knowledge is scanty and scattered. Often there are too few staff to manage the existing protected areas, which typically focus on vertebrate species. Because of the lack of resources, mollusks and other less charismatic groups are usually ignored. Nevertheless, regional and species-specific conservation action plans must be developed on the basis of appropriately designed scientific studies, such as that undertaken in the United Kingdom for conservation of the land snail V. moulinsiana (Tattersfield 2003, in Lydeard et al. 2004). To develop such plans, greater integration, coordination, and networking among conservation management agencies, research institutions, and other stakeholders is essential. This approach will ensure that conservation is scientifically based and will help to avoid potentially disastrous ecological, economic, or legal consequences. Furthermore, local and national governments and their agencies, and nongovernmental organizations of all kinds (from international organizations to local conservation societies), must forge relationships to ensure that their goals are not competitive or contradictory and that their actions are in concert. Molluscs must not be ignored when new conservation areas are created. Both new and existing reserves must be adequately managed, with attention paid to mollusks, and in some instances reserves should be established explicitly for molluscs (Lydeard et al. 2004).