New Zealand's oceans have been absorbing the impacts of climate change – but it's unclear how much more they'll be able to take.
The Government's latest environment stocktake, focused on oceans and coasts, singled out climate change - along with pollution, activities like fishing and threatened habitats - as the biggest issues facing our blue backyard.
The report found how New Zealand's coastal waters have been warming by between 0.1C and 0.2C per decade on average.
Further, years with an average temperature above the long-term average were becoming more frequent.
"New Zealand's oceans act like a giant sponge against the effects of climate change," Secretary for the Environment Vicky Robertson said.
"It's likely our seas take up more carbon dioxide than our forests, but there is only so much the oceans and the life in them can take – and the limits aren't yet known."
The warmer the water became, the less able it was to absorb gases like carbon dioxide.
"The growth of species in the oceans is affected, and coastal communities and habitats are at risk from flooding and sea-level rise."
Long-term measurements off the coast of Otago now showed a 7.1 per cent increase in ocean acidity over the past 20 years.
Shellfish like oysters, paua and mussels would become increasingly threatened as oceans became more acidic as a direct result of CO2 being absorbed.
At the same time, the rate of sea level rise had increased: the average of the past 60 years (2.4mm per year) was more than double that of the previous 60 years (1.2mm per year), and recent data suggested an even faster rate.
Extreme wave events may be becoming more frequent, while marine heatwaves were having huge effects on sea and land.
During the unprecedented 2017/18 marine heatwave in the South Island – a freakish system that partly fired a record-hot summer - bull kelp suffered losses in Kaikōura and was completely lost from some reefs in Lyttelton.
MUD AND PLASTIC
Humans were having more of direct impact through the pollution we were sending into our waters.
Some pollutants, like pharmaceuticals and cleaning products, were winding up in the marine environment – and scientists didn't yet fully understand their impact.
Plastic was continuing to be found throughout the ocean - and inside shellfish, fish, and birds – at a worrying rate.
Citizen science data collected at 44 sites showed more than 60 per cent of beach litter was plastic – and about 11 per cent of that came from cigarettes.
And coastal water quality, although improving at a national level, remained "variable", with some sites worse than others.
Our activities on land - especially agriculture and forestry, and growing cities – were driving up the amount of sediment, nutrients, chemicals, and plastics that entered our coasts and oceans.
Inter-tidal sedimentation rates had generally increased and became highly variable since European settlement.
Sediment - made up of fine particles like silt, mud, and organic material that got carried in water – was being washed from pastures, forests after felling, and urban development sites.
It filled in the spaces used by fish and invertebrates for hiding and breeding, making their food harder to find or to eat.
Thick deposits of sediment could even smother animals – and in estuaries and harbours across the Waikato region, sediment accumulation rates had risen by almost 200 times the historical rate.
HABITATS UNDER THREAT
That came as a large proportion of our marine species were already under pressure.
Of the small number assessed, 22 per cent of marine mammals, 90 per cent of seabirds and 80 per cent of shorebirds were threatened with, or at risk of, extinction.
Nearly half of the world's dolphins, porpoises and whales, some of which are endangered, have been recorded in New Zealand waters.
But it wasn't just the big creatures: in Ōhiwa Harbour in the Bay of Plenty, for instance, numbers of kuku, or green-lipped mussel, had fallen from 100 million to 500,000 in just a decade.
All the while, the number of established non-native species – many of which could spread rapidly and threaten endemic ones - was rising and now totalled 214.
The report also looked at the toll of activities like shipping and fishing, which came with wide-ranging effects on habitats.
Since 2009, the total commercial fishing catch had remained stable at less than 450,000 tonnes per year.
Last year, 84 per cent of routinely assessed stocks were considered to be fished within safe limits – an improvement from 81 per cent in 2009.
Of the 16 per cent that were considered overfished, nine stocks had collapsed.
Seabed trawling and dredging had also decreased in the last 20 years.
About 24 per cent of the fishable area had been trawled since 1990, with shallow areas trawled more extensively than deeper areas, with varying impacts.
While bycatch rates of seabirds and marine mammals were falling, this still posed a big problem – over the 2016/17 fishing year, some 4186 seabirds were accidentally caught.
New Zealand's Exclusive Economic Zone is 20 times larger than its land mass and supports a blue economy estimated to be worth $4 billion a year.
Around 80 per cent of New Zealand's flora and fauna can also be found in its 4.4 million sq km marine estate - yet scientists have only identified less than one quarter of the species they believed live there.
They were, on average, discovering seven new marine species every fortnight, which was faster than they could even name and classify them.
"It may be challenging, but it is absolutely critical that we continue to extend our knowledge and understanding of our precious marine ecosystems – our oceans, estuaries, coasts, and harbours, and the life within them," Government Statistician Liz MacPherson said.
"We're expanding the breadth of our data with the help of community organisations and our Treaty partners.
"For example, I'm especially pleased that this report includes, for the first time, data drawn from a citizen science project – the Sustainable Coastlines beach litter initiative."
But she said there was much more to be done.
"We need to align, co-ordinate, and leverage efforts across knowledge and reporting systems, including te ao Māori."
Niwa marine scientist Dr Matt Pinkerton said it was clear that the past was an increasingly unreliable indication of the future, "so we will need to do things differently".
"It is not possible to fight the many-headed challenges facing our marine environment without better long-term information on the issues facing our coasts and oceans.
"And getting better information means harnessing the burgeoning power of new technology for ocean observation."
He believed the report should be a "call to arms" to New Zealand.
"We need to commit to better marine observation, to improving our scientific understanding of complex threats, and to developing innovative, cross-agency approaches to managing, using and protecting our marine environment."
Earlier this month, Niwa coastal physicist Dr Joanne O'Callaghan said there was no coherent plan that allowed scientists and other groups to monitor our oceans in what was a changing climate.
In a new paper, she has proposed bringing together oceanographers, data scientists and other marine experts to create a sophisticated new ocean observing system.
Its benefits could include everything from being able to predict coastal hazards and oil spill trajectories to tracking plastics in the ocean and making assessments of fisheries stocks.
And earlier this year, researchers polled New Zealand marine scientists to pinpoint the biggest priorities for ocean science.
Their paper narrowed down 10 key questions across nine areas: fisheries and aquaculture, biosecurity, climate change, marine reserves and protected areas, ecosystems and biodiversity, policy and decision-making, marine guardianship, coastal and ocean processes, and other anthropogenic factors.
Those questions ranged from what impact ocean acidification would have on marine resources, and where and how should we set up more marine protected areas, to how trawling and dredging could be affecting productivity on continental shelves, and how we could pick up "tipping points" in ocean ecosystems before it was too late.