JONATHAN DOW
The dreaded teredo worm has invaded the Nuhaka River and the "termite of the sea" is now being blamed for the collapse of the Nuhaka rail bridge last month.
After examining the two wooden bridge piers that failed, sending a 60-tonne rail crane tumbling into the river, Ontrack investigators have
found the timber below the salt water line had been weakened by attack from the teredo worm.
The worm had not previously been detected in the Nuhaka River and Ontrack normally only checked for it on bridges on the rail network much further north, Ontrack head William Peet said.
Climate change could be to blame for bringing the worm to Nuhaka and Mr Peet said a NIWA scientist was investigating that, and helping to identify the marine organisms in estuaries.
"There was no history of the worm's presence in this estuary and few signs in the inter-tidal area that a suitable micro climate for the organism existed," he said.
Mr Peet said the investigation would establish the exact cause of the bridge's collapse.
Commonly known as the ship or pile worm, the teredo is actually a bivalve mollusc which invades wood as a tiny larvae and grows quickly to between six inches and six feet in length.
The teredo has been described as a nightmare for waterfront property owners as it turns wood into a brittle honeycomb.
As a precautionary measure all 48 other timber bridges crossing estuaries on the rail network had been checked by divers. They found three bridges had been attacked by the teredo worm and these had been repaired, Mr Peet said. "It has affected some piles, but its presence is sporadic rather than endemic," he said.
The 120m long steel and timber bridge on the Napier-Gisborne railway should be repaired by the end of this month, Ontrack said.
