Victoria University researchers have discovered a surprising number of animal ecosystems in Wellington's shallow waters.
The ecosystems, known as marine animal forests, were found by researchers Professor James Bell, Dr Valerio Micaroni and Dr Francesca Strano in several sites including Wellington Harbour, many at depths of less than 15 metres.
"Marine animal forests are habitats formed by big groups of invertebrates - creatures such as sponges, horse mussels, and brachiopods, which look a bit like clams," Bell said.
Micaroni said finding animal-dominated ecosystems in such shallow waters was surprising "as these are areas that are usually dominated by seaweeds."
Researchers find 'animal forests' in Wellington's shallow waters
Bell said they had conducted a number of studies around the Wellington region looking to understand where its biodiversity is located.
This one focused on the Wellington Harbour, South Coast and the Kāpiti Coast.
"Wellington Harbour has a whole range of these really cool underwater communities that are dominated by these different animals," Bell said.
Researchers were surprised to find animal-dominated ecosystems in the shallow waters of areas like Wellington Harbour. Photo: RNZ
Animal forests were found in other areas including Eastbourne, Evans Bay, Kaiwharawhara, the Miramar Peninsula, and Petone, as well as Mana Island.
"If you go diving over in Shelly Bay, down to about 10 or 15 metres, you'll see these cool areas that are covered in sea squirts and sponges and brachiopods," Bell said.
While over at Kaiwharawhara he said there were "cool sponge beds".
Sponges were one of the common species found in the forests.
Among them was a large potato-shaped sponge that grew up to 40 centimetres in diameter and formed dense sponge beds.
"These beds were home to a range of species, including molluscs, cnidarians, and red algae, as well as other sponges and fish," Strano said.
Strano said they also discovered "what we think is a previously undescribed sponge species".
The sponge beds in the harbour comprised a total area of 120,000 m2.
Researchers estimated the beds could filter between 500 million to 1 billion litres of water daily, which transferred nutrients to the sea floor and influenced the overall water quality.
Victoria University researchers had conducted a number of studies around the Wellington region looking to understand where its biodiversity is located. Photo: RNZ / Screenshot
At most of the sites in Wellington Harbour, researchers found litter on the sea-floor.
"There was a lot of plastic items such as bottles, packaging, and cups - as well as aluminium cans. Car parts and tyres were found at half the sites, and fishing gear was found at three locations. Concrete blocks were also common," Bell said.
Evans Bay was the worst site for marine litter, followed by Kaiwharawhara.
At Kaiwharawhara large amounts of gravel had been dumped on areas of the seabed, dramatically altering the habitat and reducing the animal communities.
Senior coastal scientist at the Greater Wellington Regional Council Dr Megan Melidonis said it highlighted the significant effects human activities could have on marine animal forests.
"It also highlights the need to protect these fragile ecosystems to avoid further biodiversity loss," she said.
The council helped fund the research as part of work to explore and map the region's marine biodiversity.
Melidonis said this work would help them protect the coastline.
"These forest communities play such a key role in marine food chains and in maintaining water quality. It is incredible to find them in a harbour adjacent to a major urban area," Melidonis said.