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

Large areas of Fukushima's forests were contaminated with radiocesium ( Cs) after the Fukushima Dai-ichi Nuclear Power Plant accident. Most of the contaminated forests have not been decontaminated, and bioavailable Cs 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 Cs in the spider could serve as a proxy for Cs contamination of these arthropod communities. We also examined whether N. clavata could serve as a proxy for soil bioavailable Cs. Nephila clavata was similarly or more contaminated with Cs compared with lower-trophic-level arthropods such as herbivores and other predators at the same trophic level. Thus, the Cs activity of N. clavata could represent the extent to which the arthropod community was contaminated with Cs. Data from nine Cs-contaminated sites in Fukushima showed a significant positive correlation between soil bioavailable Cs and N. clavata's Cs activity05 but the coefficient of determination was only moderate (R = 0.43), suggesting that N. clavata is only a weak proxy of soil bioavailable Cs. Our results also showed that the bioavailable fraction of Cs 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 Cs and the Cs activity in N. clavata, respectively. These results improve our understanding of Cs transfer from the soil to arthropod species.