Local Focus: Worm threatens birds

An Australian invader is choking Napier's Ahuriri Estuary, threatening endangered species.

Ficopomatus enigmaticus, commonly know as a tubeworm, has been in the estuary close to Hawke's Bay Airport for more than 20 years but a recent population explosion has caused reefs to form, stopping tidal flow.

In a joint project with Mana Ahuriri Trust, the hundreds of tonnes of tubeworm structures are being removed.

But a digger can only reach partway across the upper estuary so staff from Department of Conservation and Hawke's Bay Regional Council are chipping away at the coral-like structure by hand, and bringing it close to land for collection by the digger.

The council's senior scientist for coastal quality, Anna Madarasz-Smith, said the estuary was the most significant between East Cape and Wellington.

"It is one of our true treasures," she said.

"It is home to the critically-endangered bittern and it is one of the few areas in New Zealand where bittern are actually increasing in their numbers and that is likely due to the efforts of the Department of Conservation and particularly Hans Rook."

Godwit arrived from each September for feeding unil the end of summer.

"They fly all the way from Alaska - it takes them nine days straight - and by the time they get here they need good food to eat so they can make the return trip to breed.

The tubeworm likely arrived in ballast water from a ship visiting the nearby Napier Port, but why its population recently exploded remains a mystery.

Madarasz-Smith said tidal flow is as important to the estuary as breathing is to a person.

"We need this removal programme done before the dry summer period, so the estuary can benefit from better flushing, and a more natural tidal flow of moving water."

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