'Dead zone' rings alarm bells for society

They call it a "dead zone".
On the surface, it's a carpet of slippery, slimy, green sludge.
Beneath it is a thick layer of black mud.
But it's what's below this patch of mud in the Waikareao Estuary in Tauranga Harbour, where mangroves were mulched four months ago, that is worrying local members of the Royal New Zealand Forest and Bird Society.
Al Fleming, the society's central North Island field officer, digs a few feet beneath the mud to find a twig among mulched mangrove which he said should have decomposed months ago.
Mr Fleming fears that this patch of mulched mangroves along with the rest of the 80ha of mangroves mechanically removed elsewhere last year under the Bay of Plenty Regional Council's programme will remain dead zones for a decade - and maybe longer.
Mr Fleming said many different species such as titiko mud snails and crabs could not live in the dead zones.
Forest and Bird was also worried how the Percursaria percursa algae - more commonly known as "algal snot" - found around the surface areas had not been observed in the North Island before.
The group has long been against the removal programme, and opposed the Bay of Plenty Regional Council's application for resource consent.
The group has now called an emergency meeting with regional councillors and officers with the hope the removal of the remaining 30ha of mangrove, due to start this month, will be delayed until alternative methods for removal of the mulch have been looked at.
Forest and Bird has also suggested that the National Institute of Water and Atmospheric Research (NIWA) should monitor the health of the harbour at both the areas already cleared of mangroves and those where new methods could be trialled.
As part of a coastal ecosystems study, NIWA has been taking samples from the removal sites at Waikareao, Waikaraka and Te Puna.
In November, NIWA scientist Carolyn Lundquist told delegates at the New Zealand Coastal Science conference how short-term results of the study found that the mulch was not dispersing, posing "unprecedented adverse impacts on recovery".
But Robyn Skelton, land resources manager for the regional council, said regular monitoring of the areas where removal has been done had to date found "no significant environmental or scientific issues".
Ms Skelton said historical information from other estuaries in New Zealand indicated that mulch generally decomposed or was flushed out through tidal movement.
The council did not have a specific timeframe for the decomposing or flushing, but had a monitoring programme in place, she said.
Ms Skelton said the algae was "not unexpected" following the removal.
"At this stage, our scientists have advised that the algae is not an issue and therefore we will not be taking any action.
"At this time we are very happy with the monitoring that is being undertaken and don't see any requirement to use an external agency to carry out work that we are capable of doing ourselves.
"However if we did feel there was a need to get NIWA or any another agency involved then we would take the appropriate action to ensure we have the best possible scientific information available," she said.
Ms Skelton added:
"At this stage we don't anticipate delaying this work, however if issues are raised that haven't been previously considered then we would certainly want to resolve these to the best of our ability before proceeding."
Al Fleming (pictured front) of Royal New Zealand Forest and Bird Society says "dead zones" have been left by the Bay of Plenty Regional Council's mangrove removal programme.  Pictured with him at Waikareao Estuary in Tauranga Harbour (from left) are society members Alyn Ware, David Dowrick, Richard James, Marlene Ware, Ann Graeme, Eddie Orfulich and Basil Graeme.