13 Oct 2022

Marine heatwaves and rising sea levels: Report details impact on NZ

12:16 pm on 13 October 2022
Waves crash against a sea wall near the end of Wellington Airport

Waves crash against a sea wall near the end of Wellington Airport. Photo: RNZ / Angus Dreaver

Severe marine heatwaves, as well as hotter, more acidic waters are on the rise in the latest stocktake of New Zealand's marine environment.

The new report, by the Ministry for the Environment (MFE) and Stats NZ, backs up growing research that sea levels are rising fast.

Our Marine Environment 2022 is the third report on the state of the country's marine environment.

It brings together previous research, including that sea levels are rising twice as fast as previously thought, and new findings to paint a picture of the state of our marine environment.

The state of the sea

Latest data now shows ocean acidification is up 8.6 percent, from data collected between 1998 and 2020.

Marine heatwaves are becoming more frequent and severe, and on average the sea-surface temperature increased by 0.1C to 0.2C per decade across the four oceanic regions.

Minister of Oceans, Fisheries and Environment David Parker told Midday Report sea temperature changes posed one of the greatest risks.

"We've seen that last summer with thousands of salmon dying in marine farm every day in the Marlborough Sounds region because of changing sea temperatures."

While there some aspects the country could improve on, like reducing carbon emissions, even that wouldn't be enough to stop climate change, Parker said.

Murky waters are becoming more common, with measurements for visual clarity across the country on the decline.

Coastal water quality is also degrading as it becomes increasingly polluted with faecal contamination and dissolved oxygen.

More sites did have an improvement in the rate of pollution for things like nitrogen and phosphorus.

Between 2006 and 2020, 38 percent of water sites had worsening trends of Enterococci, an indicator of the suitability for recreation.

Plastic pollution is rising steadily, making up 70 percent of litter found along the coastlines.

The report confirms previous research that sea levels are rising as fast rates, and in some areas it has doubled in the least 60 years.

Wellington, Dunedin, and Lyttelton sea levels rose twice as much in the last 60 years compared to the previous six decades.

Preliminary data suggests extreme wave events are increasing in the east and south of the country, but decreasing on the North Island's west coast and north of the Bay of Plenty.

Despite a decline in commercial trawl and dredge tows, accidental capture of marine species remains a "significant pressure" on some species.

Those in the firing line

MFE deputy-secretary joint evidence, data and insights Natasha Lewis said when the marine environment was under stress it could affect things important to New Zealanders.

"For example, climate change is causing sea level rise, which impacts coastal communities, sites of cultural and ecological significance, and marine species. Sedimentation and pollution affect water quality, which can threaten biodiversity and public health," she said.

Parker said one of the positive changes over the past two years was a 5 percent decrease in nitrogenous artificial fertilisers going down rivers and into the sea.

"So there are fewer algal blooms than used to be the case ... that's good a trend but we've still got plenty of work that we need to do on land, particularly around sediment."

On getting sediment loss under control, he said the national policy statement on freshwater management had been upgraded and $100m was being spent in Kaipara Harbour, between Auckland and Northland.

Coastal communities, or over 72,000 people are currently at risk of coastal flooding, as are almost 50,000 buildings.

Thousands of kilometres of roads and water pipes and $26 billion worth of buildings are vulnerable to sea level rise of 0.6m.

Wāhi tapu and marae along the coastlines are also prone to risk.

Marine species and ecosystems are likely to be impacted by the increasingly hot, acidic, and rising waters.

For example, in acidic waters shellfish struggle to grow and reproduce, and corals - which support a wide variety of sea life - can die

Three-quarters of identified taonga species are threatened or close to threatened by extinction, and most sea and shorebirds are threatened, the report showed.

There was new evidence that rising seas and storm surges were taking out nesting sites for shorebirds.

It comes after global research suggests a rare third year of La Niña conditions is likely. That would bring conditions for flooding in the north and drought in the south of Aotearoa this summer.

Reactions to report

Forest and Bird are calling for the government to step up, saying the situation is an ocean crisis.

Its climate spokesperson, Geoff Keey, said bottom trawling and coal mines need to be stopped.

"We need to clean up the water that's flowing down our rivers and coming out of our pipes into the sea, and we need to have a programme to deal with marine plastics."

Minister Parker said there were several initiatives in place to minimise the impact of plastics including the Plastics Innovation Fund, a ban on some hard to recycle plastics, and coming up with biodegradable alternatives.

NIWA oceanographer and University of Auckland professor Craig Stevens said there were still a number of unknowns for marine research and their impacts, but disruption was likely.

"If a marine heat wave arrives on a coastal region around New Zealand it will really be difficult on the marine ecosystem, and the industries and social uses," Prof Stevens said.

"If you imagine that happening for several years in a row... I think some of the surprises will come in how we restructure what our coastal environment looks like."

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