Nature at work on Rena wreck below the waves

The ocean is fighting back as the Rena sits stranded on Astrolabe Reef but concern continues to mount over the wreck's sunken contents.

The container ship's gutted shell sits precariously on the underwater mountain, seven kilometres north of Motiti Island off the Tauranga coast.

The 2011 grounding was New Zealand's worst and most expensive environmental disaster. Nearly three years later more than 340 containers litter the ocean floor.

In 2012, the Rena's stern section sank to sit 65 metres below the surface in several pieces.

But the containers have local tour operator Mark Tucker on edge, despite signs an ecosystem has bounced back.

"My concern is that those containers will eventually bust open and whatever is in there is going to end up in the water, on our beaches and in our water system," Tucker said.

In 2011, debris was a regular feature on the ocean's "current lines". While it was treacherous for boatowners, pods of dolphins could be seen playing in the flotsam, he said.

A few months later, after an efficient multipronged beach cleanup and the power of the ocean to disperse the debris, business was looking up.

"Mother nature sorted it out pretty fast actually," he said.

Winter has descended on his dolphin-watch business, Orca Wild Adventures, but he was eager to get back on his boats for the coming tourist season.

"We haven't had any detrimental effects on the environment. Within about four months of the Rena going aground it was really starting to clean up."

He said the seahorse population was decimated and blue penguins were "severely smacked".

He wanted the wreck removed but said it may be impossible to complete the job safely and the community may have to wait until nature took its course.

Penguin expert Julia Graham said oil-affected birds were breeding again.

"The first year or so there was a little bit of impact on their breeding but they seem to be back on par with the non-oiled penguins now."

Bunker oil and foam lining continued to wash ashore during storms and "Rena beads" have been recently found on sandy beaches and were a risk to birdlife.

"They look like fish eggs. They [birds] swallow them and can't process them until they fill up and they literally starve to death."

Suggestions the wreck could be a haven for divers were brushed aside at Waitangi Tribunal hearings this week, but Graham said it could still be a valuable artificial reef for marine species.

"If it is almost all gone it might be best to leave it there as an ecosystem habitat. They've spent the last three years trying to re-establish in that area - all your wildlife, your little mussels and sprats. Ripping it out may not work."

Waitangi Tribunal hearings into claims the Crown breached the Treaty in its handling of the Rena wreck wrapped up in Tauranga on Wednesday.

Parties were given until July 31 to file their final closing.

The Tribunal will then consider the claims and issue a report on its findings. No date has been set for that.

Waikato Times