A sperm whale flashes its tail above the Kaikōura Canyon, off the South Island coast. Photo / File
A sperm whale flashes its tail above the Kaikōura Canyon, off the South Island coast. Photo / File
One of our largest earthquakes all but wiped out life within it, but the biologically rich environment that is the Kaikōura Canyon has bounced back faster than scientists had first expected.
Invisible to us at the surface, the undersea canyon is a massive geological structure that comes within just 500m of the coast near Kaikōura township, and feeds sediment into the sprawling, 1500km-long Hikurangi Channel east of New Zealand.
Its depths provide an incredibly productive ecosystem for many of Kaikoura’s world-famous deep-diving species, among them sperm whales, humpback whales, Southern right whales, orca and several dolphin species.
When a magnitude 7.8 event struck in November 2016, the impacts on seabed species in what is New Zealand’s only deep-sea marine reserve were catastrophic.
Some 850 tonnes of muck – or the equivalent of more than 100 million dumptruck loads of mud and sand – billowed from the canyon head, in one of the largest “canyon-flushing” events ever documented.
Only a decade before, the volume of life in the canyon’s sediment had been found to be the highest observed anywhere in the world - but this deep sea community was obliterated by the undersea avalanche barrelled through.
The deluge then travelled along the deep-sea Hikurangi Channel and its banks, where scientists later took samples of the sediment-flow deposits, known as turbidites, up to 680km northeast of Kaikōura.
The displacement wasn’t enough to trigger a devastating tsunami hitting the coast –something that had been earlier feared – while larger animals also appeared to have fared well in the disaster.
Just a few years later, researchers report the canyon’s ecosystems have recovered surprisingly well.
How the undersea Kaikōura Canyon would appear if exposed. More than 100 million dumptruck loads of sediment were flushed through it in the 2016 earthquake. Image / Animated Research, Taylormade media
“Many of the marine organisms have returned, with some parts well on the way to being fully recovered,” said Niwa and Victoria University PhD student Katie Bigham, the lead author of a study just published in the journal Frontiers in Marine Science.
With earlier surveys having captured a wealth of information about Kaikōura’s deep-sea environment, including thousands of images and datapoints, scientists had been able to compare images collected several weeks, months and years after the big quake.
Those seabed images taken shortly after the earthquake showed that the flushing event had been catastrophic for the once productive benthic community on the seafloor.
Parts of Kaikōura’s seabed are showing promising signs of recovery after the 2016 earthquake devastated marine life in the area. 👏
But within months, there was a notable increase in some species, including fish and sea cucumbers.
And within four years, the community appeared similar to the pre-disturbance community.
Niwa predicted that the whole area would be fully recovered up to 12 years after the earthquake – but it could take much less.
An earlier photograph of the seabed in the Kaikōura Canyon showing a dense cluster of juvenile sea cucumbers - indicating recovery of the deep-sea ecosystem is beginning to take place. Photo / Niwa
Niwa principal scientist and Victoria University marine biologist Dr Ashley Rowden believed it was the very nature of the volatile environment that made it such a resilient ecosystem.
“We think this habitat can so easily recover because it’s an area often at the mercy of Mother Nature. The earthquake was a one-in-140-year event, which may seem infrequent, but in evolutionary terms it’s the blink of an eye,” Rowden said.
“This means the marine life there has regularly experienced massive stressors such as earthquakes, and in turn species are adapted to be resilient to them.
“This is like when our bodies are exposed to pathogens and vaccines, which makes our immune system more resilient to disease so we can bounce back quicker.”
This image, from an earlier Niwa study, shows the amount of erosion and deposition left on the Kaikōura Canyon floor after the November 2016 earthquake. Image / Niwa
While the results of this study were encouraging for the long-term efficacy of the Hikurangi Marine Reserve, some questions remained.
“There aren’t just implications around natural pressures on deep-seabed ecosystems, but how humans interact with them, too,” Bigham said.
“We still don’t know how surrounding deep-sea fisheries were in turn impacted by the earthquake, which is a big gap because these are some of New Zealand’s most productive fisheries.
“We also want to understand how deep-sea mining will affect such ecosystems, but the findings from this study aren’t easily comparable, so more research is needed.”
The Kaikōura Earthquake was one of the most complex ever recorded, rupturing more than 21 on-shore and offshore faults along more than 100km, producing widespread coastal uplift, vertical ground movement and numerous landslides.
Studies since have revealed a world of new insights about our seismic environment – but also how such events can transform landscapes and ecosystems.
In a paper published last month, University of Canterbury and GNS Science researchers used the event as a case study to show how big quakes could make rivers change course abruptly – with serious implications for flood hazard.
