77
(37.9 ± 11.5 Bq/kg ww). In a southerly direction,
a concentration of 426.6 ± 163.5 Bq/kg ww
recorded at the Yotsukura sampling station and
closer to FNPP was higher than at the Ena station, 15 km further south. The distribution of
radioactive Cs levels in fi sh was similar to the Cs
levels in sediments (Otosaka and Kobayashi
2012 ). It is believed that this distribution is
because of the infl uence of littoral southern
currents at the accident site.
The prey–predator relationship effect was
examined using a carbon and nitrogen stable
isotope ratio analysis at the sandy sampling station at Souma. The carbon/nitrogen (CN) isotope
ratio of fi sh was in the range of −18 to −15‰ for
13 C and 12–16‰ for
15 N. Generally, CN isotope
ratios are in the range of −32 to −20‰ for particulate terrestrial organic matter, −24 to −18‰
for phytoplankton, −20 to −10‰ for benthic diatom, and −27 to −8‰ for seaweed (Fry and Sherr
1984 ; Ogawa and Ogura 1997 ). Thus, it was concluded that the food of fi sh in the sandy sampling
area of Souma consisted of benthic diatoms living on the surface seabed.
This result indicates that the main source of
primary production for fi sh in this sea area is benthic microalgae .
3.2
Diffusion via Movement/
Migration of Organisms
The number of signals received from the transmitter implanted in fi sh decreased with decreasing water temperature. However, S. cheni were
continuously recorded using the ultrasonic pinger
within the same area during the fall, winter, and
spring. Based on previous reports (Nemoto and
Ishida 2006 ), it was concluded that migration
from shallow to deep water occurred with seasonal changes in water temperature. Nevertheless,
it was confi rmed that S. cheni did not migrate but
remained in the same area and that rockfi sh were
contaminated by the radioactive Cs within this
littoral area.
4
Conclusions
Regarding diffusion via the food web, radioactive
Cs concentrations in all species decreased with
time. However, many coastal demersal species
had elevated radioactive Cs concentrations, especially fi sh. The food source of many species in
this area originates from organic matter, principally microalgae. The study of diffusion via
movement/migration showed that rockfi sh, which
had high Cs levels, tended to remain within a
small territorial area.
A study of diffusion within the body of fi sh is
now being undertaken. It is necessary to observe
radioactive Cs concentrations in marine organisms over a prolonged period of time to clarify
the distribution and variation in Cs levels, including the biological and ecological half-life in
selected marine organisms.
The Fukushima coast was decimated by the
tsunami and subsequent nuclear power plant accident. The tsunami washed massive quantities of
sand and rubble into the sea. According to the
Fukushima Prefectural Fisheries Experimental
Station, the sea urchin population was reduced signifi cantly (unpublished data); however, the infl uence on other organisms has not been clarifi ed.
Numerous coastal species were contaminated
by radioactive material, including Cs, from the
accident at FNPP (Wada et al. 2013 ). However, it
is believed that Cs contamination had almost no
infl uence on ecology or physiology function.
Currently, fi shing for 41 commercial species
is banned in waters near the Fukushima site;
therefore, there is no fi shing pressure and, in
effect, it is virtually a marine protected area.
Iwasaki et al. ( 2013 ) has predicted via a numerical study that fl atfi sh resources will increase,
aided by the fi shing ban, though it will be several
years before marine productivity of the
Fukushima coast returns to normal. Thus, for
future marine resource management strategies,
the effects of the “fi shing ban” on littoral areas
need to be examined in detail.
Distribution of Radioactive Material in Marine Ecosystems Off the Fukushima…
(37.9 ± 11.5 Bq/kg ww). In a southerly direction,
a concentration of 426.6 ± 163.5 Bq/kg ww
recorded at the Yotsukura sampling station and
closer to FNPP was higher than at the Ena station, 15 km further south. The distribution of
radioactive Cs levels in fi sh was similar to the Cs
levels in sediments (Otosaka and Kobayashi
2012 ). It is believed that this distribution is
because of the infl uence of littoral southern
currents at the accident site.
The prey–predator relationship effect was
examined using a carbon and nitrogen stable
isotope ratio analysis at the sandy sampling station at Souma. The carbon/nitrogen (CN) isotope
ratio of fi sh was in the range of −18 to −15‰ for
13 C and 12–16‰ for
15 N. Generally, CN isotope
ratios are in the range of −32 to −20‰ for particulate terrestrial organic matter, −24 to −18‰
for phytoplankton, −20 to −10‰ for benthic diatom, and −27 to −8‰ for seaweed (Fry and Sherr
1984 ; Ogawa and Ogura 1997 ). Thus, it was concluded that the food of fi sh in the sandy sampling
area of Souma consisted of benthic diatoms living on the surface seabed.
This result indicates that the main source of
primary production for fi sh in this sea area is benthic microalgae .
3.2
Diffusion via Movement/
Migration of Organisms
The number of signals received from the transmitter implanted in fi sh decreased with decreasing water temperature. However, S. cheni were
continuously recorded using the ultrasonic pinger
within the same area during the fall, winter, and
spring. Based on previous reports (Nemoto and
Ishida 2006 ), it was concluded that migration
from shallow to deep water occurred with seasonal changes in water temperature. Nevertheless,
it was confi rmed that S. cheni did not migrate but
remained in the same area and that rockfi sh were
contaminated by the radioactive Cs within this
littoral area.
4
Conclusions
Regarding diffusion via the food web, radioactive
Cs concentrations in all species decreased with
time. However, many coastal demersal species
had elevated radioactive Cs concentrations, especially fi sh. The food source of many species in
this area originates from organic matter, principally microalgae. The study of diffusion via
movement/migration showed that rockfi sh, which
had high Cs levels, tended to remain within a
small territorial area.
A study of diffusion within the body of fi sh is
now being undertaken. It is necessary to observe
radioactive Cs concentrations in marine organisms over a prolonged period of time to clarify
the distribution and variation in Cs levels, including the biological and ecological half-life in
selected marine organisms.
The Fukushima coast was decimated by the
tsunami and subsequent nuclear power plant accident. The tsunami washed massive quantities of
sand and rubble into the sea. According to the
Fukushima Prefectural Fisheries Experimental
Station, the sea urchin population was reduced signifi cantly (unpublished data); however, the infl uence on other organisms has not been clarifi ed.
Numerous coastal species were contaminated
by radioactive material, including Cs, from the
accident at FNPP (Wada et al. 2013 ). However, it
is believed that Cs contamination had almost no
infl uence on ecology or physiology function.
Currently, fi shing for 41 commercial species
is banned in waters near the Fukushima site;
therefore, there is no fi shing pressure and, in
effect, it is virtually a marine protected area.
Iwasaki et al. ( 2013 ) has predicted via a numerical study that fl atfi sh resources will increase,
aided by the fi shing ban, though it will be several
years before marine productivity of the
Fukushima coast returns to normal. Thus, for
future marine resource management strategies,
the effects of the “fi shing ban” on littoral areas
need to be examined in detail.
Distribution of Radioactive Material in Marine Ecosystems Off the Fukushima…