Declining soil Crustacea in a World Heritage Site caused by land nemertean

Shotaro Shinobe,Isamu Okochi,Satoshi Chiba,Shota Uchida,Hideaki Mori

doi:10.1038/s41598-017-12653-4

Shotaro Shinobe, Isamu Okochi + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-12653-4

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Abstract

Invasive non-native species are of great concern throughout the world. Potential severity of the impacts of non-native species is assessed for effective conservation managements. However, such risk assessment is often difficult, and underestimating possible harm can cause substantial issues. Here, we document catastrophic decline of a soil ecosystem in the Ogasawara Islands, a UNESCO World Heritage site, due to predation by non-native land nemertine Geonemertes pelaensis of which harm has been previously unnoticed. This nemertine is widely distributed in tropical regions, and no study has shown that it feeds on arthropods. However, we experimentally confirmed that G. pelaensis predates various arthropod groups. Soil fauna of Ogasawara was originally dominated by isopods and amphipods, but our surveys in the southern parts of Hahajima Island showed that these became extremely scarce in the areas invaded by G. pelaensis. Carnivorous arthropods decreased by indirect effects of its predation. Radical decline of soil arthropods since the 1980s on Chichijima Island was also caused by G. pelaensis and was first recorded in 1981. Thus, the soil ecosystem was already seriously damaged in Ogasawara by the nemertine. The present findings raise an issue and limitation in recognizing threats of non-native species.

Highlights

Invasive non-native species transported by human activities have caused serious impacts on native ecosystems[1,2,3]
The study area was in Minamizaki, which was in the southern part of Hahajima (Fig. 1b,c)
We found that land nemertine is not distributed in the southern part of Minamizaki

Summary

Introduction

Invasive non-native species transported by human activities have caused serious impacts on native ecosystems[1,2,3]. Because of the limitation of resources that can be provided for conservation in Ogasawara, all efforts to control non-native species are focused on the species listed as IASs or those with records of exhibiting invasiveness in other regions, and few surveys are provided for other non-native species. Several researchers have studied taxonomy and distribution of land nemertine in Ogasawara since 1990s28–32 This species is widely distributed in tropical regions as a non-native species, on islands[33,34,35]. In Ogasawara, G. pelaensis was not an effective predator on land snails[29] This non-native nemertine has been recognized as a species that causes no harm to the ecosystem. We test this hypothesis using feeding experiments and field surveys

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