Abstract
In 2012, after the accident at the Fukushima Daiichi Nuclear Power Plant (FDNPP) that followed the Tohoku earthquake and tsunami in March 2011, no rock shell (Thais clavigera; currently recognized as Reishia clavigera; Gastropoda, Neogastropoda, Muricidae) specimens were found near the plant from Hirono to Futaba Beach (a distance of approximately 30 km). In July 2016, however, rock shells were again found to inhabit the area. From April 2017 to May 2019, we collected rock shell specimens monthly at two sites near the FDNPP (Okuma and Tomioka) and at a reference site ~ 120 km south of the FDNPP (Hiraiso). We examined the gonads of the specimens histologically to evaluate their reproductive cycle and sexual maturation. The gonads of the rock shells collected at Okuma, ~ 1 km south of the FDNPP, exhibited consecutive sexual maturation during the 2 years from April 2017 to May 2019, whereas sexual maturation of the gonads of specimens collected at Hiraiso was observed only in summer. The consecutive sexual maturation of the gonads of the specimens collected at Okuma might not represent a temporary phenomenon but rather a site-specific phenotype, possibly caused by specific environmental factors near the FDNPP.
Highlights
The 2011 Tohoku earthquake ( Mw 9.0) on 11 March 2011 generated a tsunami that caused meltdown of three nuclear reactors at the Fukushima Daiichi Nuclear Power Plant (FDNPP), owned by the Tokyo Electric Power Company
Transport model simulations have indicated that more than 80% of the atmospheric fallout during the 2011 disaster was onto the ocean surface, and that deposition was highest onto coastal waters near the FDNPP, this evaluation was not confirmed by direct observations of atmospheric fallout over the ocean[2]
Female reproductive cycles were recognized in temporal changes in the monthly average sexual maturation scores of ovaries from T. clavigera and T. bronni specimens collected at each site (Fig. 2)
Summary
The 2011 Tohoku earthquake ( Mw 9.0) on 11 March 2011 generated a tsunami that caused meltdown of three nuclear reactors at the Fukushima Daiichi Nuclear Power Plant (FDNPP), owned by the Tokyo Electric Power Company. Quantitative surveys in 2013 showed that species richness and population densities of sessile invertebrates, especially Arthropoda, in intertidal zones were much lower at sites near the FDNPP or within several kilometers southward than at other sites, and they were lower in 2013 than in 1995. These findings strongly suggest that the intertidal biota around the power plant was affected by the nuclear accident[13]. These findings suggest that environmental factors inhibited invertebrate reproduction, recruitment, or both in the intertidal zones near the F DNPP14
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