Warming waters are placing New Zealand’s kelp forests in peril - posing troubling implications for the plethora of ocean species that rely on them.
Warming waters are placing New Zealand’s kelp forests in peril - posing troubling implications for the plethora of ocean species that rely on them.
Warming waters are placing New Zealand’s kelp forests in peril - posing troubling implications for the plethora of ocean species that rely on them.
While years of relentless marine heatwave conditions around the country have turned a spotlight on the dangers our undersea ecosystems face under climate change, until now, scientists hadn’t pooled information about this risk together.
In their just-published study, a team led by Victoria University’s Dr Christopher Cornwall investigated the effects of several “stressors” on seaweed ecosystems likely to worsen as our planet continued to heat.
They were marine heatwaves, ocean acidification and warming, and “coastal darkening” - or changes in the colour and clarity of our coastal waters.
In most cases, Cornwall said, the disruption each of these stressors could have would likely be irreversible.
“Our conclusions show the range and health of many of our seaweed species will shift, with sensitive species such as giant kelp most affected,” he said.
“Once they’re gone, it will be very difficult to restore ecosystems back to how they were.”
Recent marine heatwaves have already wrought a dramatic toll on kelp forests in parts of New Zealand.
Last year, the Department of Conservation blamed abnormally warm waters for the disappearance of 90 per cent of bull kelp in the West Coast’s Punakaiki Marine Reserve, while in 2018, a marine heatwave wiped out the bulk of native kelp in Lyttelton Harbour.
They’ve also caused shifts in grape-growing seasons, record glacier melts in the Southern Alps, mass sponge bleaching events in Fiordland, salmon farm die-offs in the Marlborough Sounds and brought species like snapper and kingfish into the typically colder waters of Southland.
This year, scientists reported how marine heatwaves had been disrupting the local feeding and breeding of our own population of the planet’s largest animal: the blue whale.
As far as our seaweed communities mattered, Cornwall described them as “economically, environmentally and culturally crucial.
“Seaweed ecosystems, including kelp forests, are our most important undersea nurseries and habitats,” he said.
“They provide food, shelter, and other ecological services to species such as pāua, kina, and koura (crayfish), as well as an array of fin-fish species—including moki, blue cod, and snapper.
“All these species will suffer, or cease to exist in some cases, if seaweed ecosystems die.”
Kelp forests are important habitats for a range of ocean species, including koura (crayfish). Photo / Andrew Warner
Earlier research by Cornwall observed similar effects from warming waters on the world’s coral reef ecoystems.
“We’ve seen a lot of damage already with mass coral bleaching events caused by marine heatwaves,” he said.
“Corals’ ability to persist and continue growing will be strongly influenced by ongoing warming.”
At the same time, recent studies have pointed to marine heatwaves growing longer, stronger and more frequent in New Zealand.
Our seas have been warming by an average 0.2C per decade - and that pace of heating is quickening.
On top of what we’re already witnessing, scientists have warned that average sea temperatures could rise by 1.4C within four decades – and almost 3C by the century’s end.
That would mean that, by mid-century, we could be facing 260 days of marine heatwaves per year – and 350 days by 2100 – compared with the 40-odd days we see now.
“I think the majority of the public have no idea of the magnitude of what is approaching,” Cornwall said.
“Seaweed forests may not receive as much attention globally as coral reefs, but they are just as important and just as at risk.
“We need better marine protection policies, including protection from overfishing beyond marine reserves and proper ecosystem-based management at the reef level.
“Alongside this, we need restoration efforts that attempt to breed more temperature and low-light resistant species - without this, the prognosis is not great.”
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
