Tokyo

A huge land reclamation project in southwestern Japan is to be halted and partially reversed while researchers investigate its implications for marine biodiversity.

Flood of protests: the dyke at Isahaya bay has been blamed for damaging the local ecosystem. Credit: KYODO PHOTO SERVICE

The move is seen as a significant victory for Japanese ecologists and seaweed farmers. The agriculture minister Yoshio Yatsu announced last week that the gates of a large dyke at Isahaya bay will be opened at some point while the study is done. Some ecologists believe that this will help the local marine ecosystem to recover.

Poor seaweed harvests and fishery catches led the agriculture ministry to ask an independent panel, chaired by Makoto Shimizu, a former University of Tokyo agriculturist, to look into the reclamation programme. The panel found that uncontrolled growth of diatom plankton was responsible for upsetting the ecosystem and depriving seaweed of nutrients.

Many ecologists blame the dyke, which was built in 1997 as part of a ¥249 billion (US$2 billion) project to reclaim land around the bay for farming. The dyke created a reservoir inside the bay where sea water is purified into fresh water, a process that kills the clams and other shellfish that live in it. These shellfish would normally eat the plankton, which has since been free to grow out of control.

The panel recommends that the dyke's gates be opened during a two-year study of the dyke's effects on seaweed growth. But it suggests delaying this action for up to a year to allow for safety measures to be taken against possible adverse outcomes such as flooding.

An agriculture ministry official says that it is still “considering other hypotheses besides the dyke” as the cause of the plankton growth. These include the impact of the nearby city of Fukuoka's diversion of water for drinking from a river that feeds the bay.

But some ecologists are critical of the delay in opening the gates. “There is no time to question which factor is most important — we must try to restore the ecosystem before it is too late,” says Masanori Sato of Kagoshima University's environmental science department.