Kaikoura Earthquake: How a valley seal bounced back from its near extinction

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A sperm whale flashes its tail over Kaikoura Valley off the coast of the South Island. photo/file

One of the largest earthquakes wiped out life within it, but a biologically rich environment like Kaikoura Canyon bounced back faster than scientists initially expected.

Invisible from the surface, the Undersea Valley is a massive geological structure located just 500m off the coast near the town of Kaikoura, feeding sediment in the sprawling Hikurangi Channel 1,500km east of New Zealand.

Its depths provide an incredibly productive ecosystem for Kaikoura’s many world-famous deep-diving species, among them sperm whales, humpback whales, southern right whales, orcas, and several species of dolphin.

When a magnitude 7.8 event occurred in November 2016, the effects on seafloor species in New Zealand’s only deep-sea marine reserve were catastrophic.

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About 850 tons of mud—or the equivalent of more than 100 million loads of mud and sand—bulged out of the canyon head, in one of the largest “canyon flow” events ever documented.

Kaikoura Canyon. Image / Niwa

Just a decade ago, the volume of life in valley sediments was found to be the highest anywhere in the world—but that deep-sea community was obliterated by an undersea avalanche.

The flood then traveled along the deep-sea Hikurangi Channel and its banks, where scientists later sampled sediment flow deposits, known as turbidity, up to 680 kilometers northeast of Kaikoura.

The displacement was not enough to cause a devastating tsunami to hit the coast – something that had previously been feared – while the larger animals also seemed to have succeeded in the disaster.

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Just a few years later, researchers reported that the valley’s ecosystems had recovered surprisingly well.

How would the Kaikoura Valley appear under the sea if exposed? More than 100 million tonnage of sediment was dumped through it in the 2016 earthquake. Search Image/Animation, Taylormade Media

“Many marine organisms have come back, and some parts of them are on the path to a full recovery,” said Katie Bigham, a Newa and University of Victoria doctoral student, lead author of a study just published in the journal Frontiers in Marine Science.

With previous surveys collecting a wealth of information about Kaikoura’s deep-sea environment, including thousands of images and data points, the scientists were able to compare images collected several weeks, months and years after the major earthquake.

Sea floor photographs taken shortly after the earthquake showed that the flow event was catastrophic for the benthic community that was productive on the sea floor.

Parts of the Kaikoura Sea floor are showing promising signs of recovery after the 2016 earthquake devastated marine life in the area. 👏

Read the full story here 👉 https://t.co/pDaH8rRHDG pic.twitter.com/Ee7HdLfqlO

– Niwa (@niwa_nz) June 19, 2023

But within months, there was a marked increase in some species, including fish and sea cucumbers.

And within four years, the community looked similar to that before the disorder.

Niwa predicted that the entire region would fully recover for up to 12 years after the earthquake – but it could take much less than that.

An earlier image of the seafloor in Kaikoura Valley showing a dense clump of young sea cucumbers – suggesting that deep-sea ecosystem recovery is beginning to unfold. photo / niwa

Niwa Principal Scientist and University of Victoria marine biologist Dr Ashley Rudin believes it is the environment’s capricious nature that has made it such a resilient ecosystem.

“We think this habitat could easily recover because it is an area so often at the mercy of Mother Nature. The earthquake was one event in 140 years, and it may seem rare, but in evolutionary terms, it’s the blink of an eye.

This means that marine life there is regularly subjected to massive stresses such as earthquakes, and thus species adapt to be able to adapt to it.

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“This is like when our bodies are exposed to pathogens and vaccines, it makes our immune system more resilient to disease so we can recover faster.”

This image, from a previous Niwa study, shows the amount of erosion and sedimentation left on the Kaikoura Valley floor after the November 2016 earthquake. Photo/Niwa

While the results of this study were encouraging for the long-term effectiveness of Hikurangi Marine Reserve, some questions remained.

“Not only are there implications about natural pressures on deep sea floor ecosystems, but how humans interact with them as well,” Bigham said.

“We still don’t know how deep sea fisheries in turn were affected by the earthquake, which is a huge gap as these are some of the most productive fisheries in New Zealand.

“We also want to understand how deep-sea mining will affect such ecosystems, but the results of this study are not easily comparable, so more research is needed.”

The Kaikoura earthquake was one of the most complex earthquakes ever recorded, with more than 21 faults tearing at the beach and in the sea over a length of more than 100 km, resulting in extensive coastal uplift, vertical land motion and numerous landslides.

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Studies have since revealed a world of new insights into our seismic environment – but also how such events can alter landscapes and ecosystems.

In a paper published last month, the University of Canterbury and GNS Science researchers used the event as a case study to show how large earthquakes can cause rivers to suddenly change course – with serious implications for flood risk.

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