| LOCAL WARMING: STABILITY AND COLLAPSE OF A SUBTROPICAL FISH ASSEMBLAGE DEPENDENT ON THE THERMAL DISCHARGE FROM A NUCLEAR POWER STATION |
| MASUDA, REIJI. Maizuru Fisheries Research Station, Kyoto University, Nagahama, Maizuru, Kyoto 6250086, Japan, reiji@kais.kyoto-u.ac.jp |
| After the disaster of Fukushima, the risk of catastrophic accidents in nuclear power stations has been focused on, yet relatively little attention has been drawn to the potential negative impacts of their thermal discharge on the environment. Here I report on a peculiar fish assemblage that had been presumably dependent on a thermal discharge. Underwater visual censuses were conducted to assess the effect of power station thermal discharge on shallow water fish assemblages. Three locations along Kyoto and Fukui prefectures, central Japan, were selected for comparison: Nagahama where a typical temperate rocky reef fish assemblage observed was used as a control, Sezaki where a thermal power station started to run from the summer of 2005, and Otomi where a nuclear power station had been running since 1974 but was suspended on February 20, 2012. Four times of ca. 60 min. visual surveys were conducted in each location every winter (from late January to early March) from the years 2004 to 2012, and the number and the size of each fish species recorded. Bottom water temperature in Otomi was consistently higher with a difference of ca. 2 °C than the other two locations, except after the suspension of the power station, when there was no inter-location difference of temperatures anymore. In Nagahama and Sezaki, no major change was observed in their fish assemblages for the last nine years. In Otomi from 2004 to 2011 roughly twice as many fish species, including many subtropical species, were consistently recorded compared to the other two locations. In the winter of 2012, however, this fish community collapsed, together with a large die-off of the tropical sea urchin Diadema sp. Subtropical species are assumed to have drifted with the current from south of this district, most of which would not survive in winter except for those arriving near the thermal discharge. Although the thermal discharge of a power station is a local phenomenon, the spatial and temporal accumulation of it can substantially contribute to an environmental modification with a large scale. Furthermore observations of fish assemblages in such areas may potentially provide us with valuable information related to the possible future fish assemblages induced by global scale of warming. |
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