Densities of sessile organisms (number/m²) in intertidal zones (by elevation).

L: lower intertidal zone; M: middle intertidal zone; U: upper intertidal zone. Data were collected by using a 50-cm × 50-cm quadrat in May–June 2013. Purple star marks the location of the Fukushima Daiichi Nuclear Power Plant (FDNPP). Dotted circle indicates a 20-km radius from FDNPP. Pink dotted line represents the average number of individuals per square meter from surveys of sessile organisms conducted in May 1995 by using a quadrat method at 20 sites along the coast of Fukushima Prefecture²⁰. The average population density in 1995 was 7158 individuals/m², consisting of Arthropoda (4593, 64.2%), Annelida (179, 2.5%), Mollusca (2348, 32.8%) and other organisms (38, 0.5%)²⁰. *The partial map of Japan in this figure was modified by the authors from the map of Japan at the following website: http://www.freemap.jp/item/japan/japan1.html.