Background: After the Fukushima Daiichi Nuclear Power Plant accident, various surveys were performed to measure the extent of radioactive material contamination in the marine sediments, surface waters, plankton and fish. Six months after the event, relatively high radiocesium contamination could still be detected in the fish and sediment of the coastal demersal environment. To determine the distribution of radioactive material in the demersal ecosystem adjacent to the event, we sampled and analyzed the dominant macroorganisms attached to the seafloor as well as environmental material, including biofilms, from the coastal demersal environment around Hisanohama Port, which is less than 30 km south of the accident site. Results: Our results showed that variable ratios of radiosilver/radiocesium occurred in the macrobenthos, macroalgae and sediment samples. However, the biofilm samples displayed high radiocesium contamination but did not show radiosilver contamination. Conclusions: These findings suggest that several different entry paths are available for radioactive elements to access the biological components of the ecosystem, and these paths may explain the disproportional and patchy distribution of radioactive elements among marine ecosystems.