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Studying the biodiversity impacts of earthquakes

Examining uplifted seabed north of Kaikoura, New Zealand, at 5 days (left) and 5 months (right) after the earthquake. Most intertidal life at this site was destroyed in the quake.

In November 2016, I was in Wellington, New Zealand, about to give a public talk on my research, and was staying in a tall hotel in the city. Around midnight, the night before my talk, I was woken as my bed started to shake. The shaking got stronger, and stronger, and plaster started falling from cracks in the ceiling. I ran to a doorway, and held on. I could hear glass breaking and people shouting. The curtains were swinging around, and through the window I could see the building next door swaying from side to side. Eventually, the shaking stopped. I poked my head out of room, and saw a naked man running down the corridor, screaming "we've got to get out of here!"

The next morning, I asked around to see if anyone thought there might have been coastal uplift as a result of the quake, because I had just started thinking about designing a project to study the impacts of large-scale disturbance on intertidal communities - particularly the New Zealand bull kelps that I have been studying for a decade or so.

The earthquake (or series of earthquakes) that struck New Zealand early on 14 November reached up to 7.8 magnitude. The epicentre was in the north-east of the South Island, and communities in that region were devastated. Roads and buildings were destroyed, and the town of Kaikoura was entirely cut off for several weeks by landslides across the highway. Sadly, two people died in the quake, and many others were injured and / or had their homes and livelihoods destroyed.

The earthquake caused a great deal of damage to roads and other infrastructure. Yes, that's a major highway buried under a massive slip!

Aside from the impacts on human communities, the earthquake also caused massive uplift of the coastal seabed. From just south of Cape Campbell, to just south of Kaikoura, parts of the coast were lifted by up to six metres! Intertidal communities were left stranded, high above the water.

In the days following the quake, my colleague Prof Jon Waters (University of Otago, New Zealand) and I travelled into the affected areas and took samples of the stranded marine life. It was a mindboggling experience. We were walking through surreal landscapes - underwater worlds without water! Craypots and crayfish lay at our feet, and subtidal seaweeds dangled from rocks metres above our heads. On top of those rocks, large fish lay dead - the uplift had happened so rapidly they had not had a chance to swim away!

Jon Waters measuring uplift in the days after the quake. The rock he is standing on is capped by subtidal seaweeds - now stranded around 6 m above the new water level! Right: five months later, all the intertidal seaweeds at this site were dead.

The samples we collected from the uplifted (and flanking) sites will allow us to piece together a picture of the genetic diversity and spatial structure of intertidal marine organisms along the affected coast. We will be able to compare these 'before' patterns with those a few years down the track, once the communities recover. At sites where uplift was relatively small, and some remnants of the original populations survived (such as the Kaikoura Peninsula, where uplift was only ~1.5 m), we expect there will be very little genetic change, as the survivors will be able to 'seed' the recovery. At sites where uplift was great, however (such as Waipapa Bay, where the seabed lifted by ~6 m), populations will have been annihilated and we expect recolonisation will have to happen from dispersing creatures, which might come from far away, so we could see drastic genetic or even community change. It will be a few years yet before we get the results of this work and can start to understand the biodiversity impacts of such large-scale, catastrophic events. You can hear me talk about this project in two radio interviews, here and here.

At some sites, such as the Kaikoura Peninsula (pictured), intertidal populations were reduced but not destroyed, and should be able to make a relatively rapid comeback. Left: 5 days post-quake; Right: 5 months post-quake - some intertidal kelps were still alive, and already reproducing.

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