Thriving underwater ‘gardens’ found off Wellington's coastline

Fifty metres below the water's surface, a world of colourful sea sponges has been studied for the first time.

Nine locations off the Wellington and Kāpiti coastlines were surveyed using Kiwi-made underwater technology, allowing researchers to study a little-known marine ecosystem.

James Bell, professor of marine biology at Victoria University of Wellington, led the project.

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"What we found when we sent down our underwater drone was these amazing animal forests that were really dominated by a whole range of different, slightly unusual creatures," he said.

A lot of marine research focus in New Zealand has been on deep-sea environments below 200m, and in the shallower waters above 30m.

He says the underwater space "is a really interesting transition zone between the kind of really shallow water organisms and the deep water organisms."

The ecosystems they found were dominated by sponge 'gardens' unlike those elsewhere around the country.

"These environments are poorly known, so we don't know much about the species there," said Bell.

"For us to be able to conserve, protect and understand these environments a really good important starting place is to know what's there."

Similar depths in Northland's Poor Knights marine reserve are home to sponges known for their tree-like structures, while those down south in Fiordland are more 'encrusting'.

"In Wellington, they're quite different, they're more like little hillocks. They're really kind of three-dimensional (and) there's lots of structures and places for things like fish, starfish and brittle stars to all live in between the sponges. So they do look quite different," said Bell.

Senior environmental scientist Dr Megan Oliver from Greater Wellington Regional Council, a partner in the research programme, says "this work goes a long way to making this hidden marine world more visible so that we can take better care of it."

This is crucial because beyond being a glimpse of a new ecosystem, the new research is aiming to help in future conservation projects, says Oliver.

The Department of Conservation (DOC) also partly funded the research programme.

DOC marine ecosystems manager Mathilde Richer de Forges says the "management of New Zealand’s deep-water reefs is hindered by the lack of fundamental information on where they are, the species that occupy them, and their relationship with shallower ecosystems."

This research will help fill that void.

Forges says DOC is "also interested in understanding the potential role of these deep-water reefs to act as a buffer, or refuge for shallower ecosystems species, in response to climate change-related events such as marine heat waves,"

Oliver agrees, adding that more research is needed to further understand the risks facing these ecosystems.

"Because we simply don't know what we could be losing. We don't understand well enough as we sit here how the marine environment is changing. And it is changing right under our noses."