New Zealand's marine environment is under pressure from coastal development, shipping traffic and climate change, a new government report says.

Photo: Unsplash / Alister Hitchcock

The Ministry for the Environment's second marine report released today shows cumulative effects from land and sea-based human activity are impacting on marine ecosystems, harming habitats and allowing non-native species to thrive.

On top of that, the environment also has to deal with the impacts of climate change.

"Cumulative effects are one of the most urgent and complex problems facing our marine environment. In some instances, when effects overlap they can offset each other and reduce the overall impact, but more often effects compound, or result in unexpected impacts," the report said.

It said biogenic habitats - habitats created by plants and animals - were declining.

"Biogenic habitats play a crucial role in enhancing biodiversity by providing ecosystem services. For example a mussel bed providing shelter to juvenile fish or seagrass meadows removing and storing carbon dioxide from the atmosphere."

Most biogenic habitats, apart from mangroves, were declining.

A decline in the number of kuku (green-lipped mussel), which is also a habitat, from over 100 million in 2007, to less than 500,000 in 2016 was observed in the Ohiwa Harbour.

Eighty percent of shorebirds, 90 percent of seabirds and 22 percent of marine mammals were identified as being at risk of, or threatened with extinction.

Three new non-native species had also made New Zealand their home since the last report in 2016, and 211 others were well-established.

"Between 2010 and 2017 43 percent of the non-native marine species detected in New Zealand had established populations here and were living on permanent surfaces like rocks and piers."

The report was done in conjunction with Stats NZ and was mandated under the Environmental Reporting Act.

For the first time data from citizen scientists was used in the report, beach clean-up crews and other community groups were taught how to collect robust information.

This data helped conclude human activities on land, were severely impacting oceans, with litter and plastic debris a pervasive sediment.

Development of coastal areas, including the building of ports, wharfs, homes and seawalls were also harmful.

"Before humans arrived in New Zealand, forests grew to the water's edge. After settlement, and European settlement in particular, much of this vegetation was removed."

"An increasing population and demand for new houses close to the sea is driving coastal development and encroachment of coastal habitat. Structures like seawalls and groynes are built to protect property and infrastructure from storms and waves."

Coastal development affected local water flow and wave action leading to a change in sediment deposition and the shapes of some waterways.

"Changes to the coastline alter the way waves and sediment move and can result in intertidal habitats being lost."

"This is significant as shallower coastal environments hold the greatest diversity and turnover of species."

For example in the Waikato sediment rates were at 200 times more than before Europeans settled.

Another contributing factor was increased shipping traffic.

"Almost all of our imports and exports are transported by sea."

The highest traffic areas were the east coast, off Canterbury and the north-east coast of the North Island.

"The number of cruise ships coming to New Zealand and the number of passengers per ship grew five-fold between 2004 and 2015... The average number of passengers and consequently the size of the cruise ship has also grown."

At 37 percent, shipping is the biggest contributor to the maritime economy.

Fishing and seabed trawling pressure had eased, but was still a factor in the decline of the marine environment with some stocks still overfished.

"In 2018, 84 percent of routinely assessed stocks were considered to be fished within safe limits, and improvement from 81 percent in 2009."

"Of the 16 percent that are considered overfished, 9 stocks were collapsed, meaning that closure should be considered to rebuild the stock as quickly as possible."

Bycatch of seabirds, sea lions, fur seals and Maui and Hector's dolphins, was down on previous years, but still put "serious pressure" on some populations.

Climate Change

The report also confirmed New Zealand's sea temperature had risen and was consistent with the global average.

"The ocean has an important role in removing carbon dioxide from the atmosphere, but as oceans warm, they lose their capacity to absorb as much carbon dioxide."

It also found sea levels were rising faster than before.

"Climate projections suggest that on average globally, we can expect a rise of 0.2-0.4 metres by 2060 and 0.3-1.0 metres by 2100.

New Zealand should also expect more frequent "extreme wave events", marine heatwaves and ocean acidification.

"The pH of waters around New Zealand will decrease by 0.3 to 0.4 pH units by the end of this century... Reversing this profound change will take tens of thousands of years."

"In 2017, the aquaculture industry's estimated total revenue was $557 million, with 62 percent of this from mussels... [which are] vulnerable to ocean acidity."

During the 2017 and 2018 marine heatwaves in the South Island, bull kelp suffered losses in Kaikoura and was completely lost from some reefs in Lyttelton.

"Following these losses the empty spaces were rapidly colonised by Undaria an introduced non-native species."

"Warming waters in summer are already affecting fish. The reproduction of some fish species (like snapper and hoki) appears to be affected by sea-surface temperature. Warming and other changes to the marine environment could affect other species, and increases and decreases in stocks are possible."

Data collection

The report acknowledged "although good progress has been made to better understand our marine environment, gaps in data coverage and consistency remain. This limits some understanding and reporting."

It said marine data and in particular data about underwater habitats was difficult and costly to obtain.

"These gaps present opportunities: to develop a national picture through co-ordinated monitoring, and to grow our knowledge about specific places."