Web-building spider Nephila clavata (Nephilidae: Arachnida) can represent 137Cs contamination of arthropod communities and bioavailable 137Cs in forest soils at Fukushima, Japan

Abstract

Large areas of Fukushima's forests were contaminated with radiocesium (137Cs) after the Fukushima Dai-ichi Nuclear Power Plant accident. Most of the contaminated forests have not been decontaminated, and bioavailable 137Cs is likely to circulate within the forest environment's food web. Nephila clavata (Nephilidae: Arachnida) is a top predator in the forest arthropod community, and this web-building spider potentially consumes many arthropod species presented in the grazing and detrital food chains. We tested whether 137Cs in the spider could serve as a proxy for 137Cs contamination of these arthropod communities. We also examined whether N. clavata could serve as a proxy for soil bioavailable 137Cs. Nephila clavata was similarly or more contaminated with 137Cs compared with lower-trophic-level arthropods such as herbivores and other predators at the same trophic level. Thus, the 137Cs activity of N. clavata could represent the extent to which the arthropod community was contaminated with 137Cs. Data from nine 137Cs-contaminated sites in Fukushima showed a significant positive correlation between soil bioavailable 137Cs and N. clavata's 137Cs activity05 but the coefficient of determination was only moderate (R2 = 0.43), suggesting that N. clavata is only a weak proxy of soil bioavailable 137Cs. Our results also showed that the bioavailable fraction of 137Cs in Fukushima was strongly correlated with the total inventory and that the K and Na contents of the soil determined the soil-to-spider transfer factor for 137Cs and the 137Cs activity in N. clavata, respectively. These results improve our understanding of 137Cs transfer from the soil to arthropod species.