Shanti Mathias spends a day in the Hauraki Gulf with a group of British scientists investigating the links between carbon and biodiversity in the seafloor mud.
The ocean swell is tilting the boat as the metal tube hovers above the water. “A-Frame out,” calls a marine scientist helping to operate the apparatus. On the back of the boat, researchers Tara Williams and Ben Harris lean out, unclipping the base of the tube from two stabilising ropes, the navy of Williams’ shark tattoo the same colour as the dark ocean. The skipper starts the winch, bright yellow rope unspooling as the sediment corer sinks to the bottom of the sea, then everyone works together to feed out the electric cable that powers the sediment corer. Each metre of cable, black and dense, weighs about a kilo. Finally, the cable and rope stop moving; the corer has reached the sea floor.
The corer gets switched on. Nearly a hundred metres below, the part of the device that my notes describe as “slicy thing” springs open, shudders through the soft mud, then seals up. Then the whole process happens again in reverse: heavy cable reeled hand over hand, the gawky corer spinning slightly as it comes out of the sea, the machine latched in place so Harris can slide the plastic tube out, khaki mud spurting all over his grey hoodie.
We’re aboard the University of Auckland’s Te Kaihōpara research vessel, a few kilometres out from shore in the Hauraki Gulf. These scientists from the University of Exeter in the UK, (although the boat is operated by a skipper and fish expert/senior technician from the University of Auckland), have been in the area for a month as part of the Convex Seascape Survey, the logo of which is plastered around the boat and on the scientists’ clothing. The survey is a research effort dedicated to discovering how much carbon is stored in the soft sediments of continental shelves – and how much more could be if these areas are protected. The project is funded by the CEO of Convex Ltd., an insurance company.
The partnership between Convex, the charity Blue Marine Foundation and Exeter is a glimpse of what it takes to make long-term, groundbreaking research happen. A year and a half into a five-year project, the plan is to sample soft sediments from the seafloor in a variety of locations while also analysing biodiversity big (fish) and small (worms living in the mud). So far, the team has been to Jersey, Scotland and Aotearoa; after this trip, they’ll have to figure out their next destination.
The Hauraki Gulf is ideal to study, not just because of the resources of the University of Auckland’s Leigh Marine Lab, but also because of a cable protection zone. While it’s not obvious from the surface of the water, areas of the seafloor are protected from bottom trawling to avoid damaging extremely expensive undersea cables. This makes it possible to compare the biodiversity and carbon content between areas with and without bottom trawling.
“Blue carbon”, a term encapsulating how much CO2 is absorbed by marine ecosystems, is something of a buzzword at the moment. It’s now known that ecosystems at the edge of the water, like salt marshes and mangrove swamps, can absorb huge amounts of carbon relative to how much area they occupy. A group in the UK has just mapped the blue carbon of the British coast, while a NIWA project is quantifying how much carbon gets absorbed by kelp. With climate targets making measuring and storing carbon for offsets a big business, blue carbon has gained both research and commercial interest.
The reason that this part of the Hauraki Gulf is protected – not for the inherent value of biodiversity, but to protect human infrastructure – is an example of the warped logic underpinning carbon offsetting, says Ben Harris, who is leading the Convex Seascape Survey team in New Zealand and has the tan of someone who has been spending lots of time outside. “Even if you could perfectly calculate [the volume of carbon offset] the principle is just wrong. It’s mental; you’re just kicking the can down the road,” he says. But through human cynicism, the marine life he loves might be protected too. “If people jump on blue carbon because they’re like ‘oh great, we’ve got these carbon credits’ then biodiversity will slip in through the back door.”
Is he worried that his research can be used as a justification to keep emitting? “There’s this cynical kind of element which is that large organisations can benefit from offsetting their carbon – if they decide ‘we can put in, I don’t know, $50 million and protect this area for this many carbon credits’ they would say yes. The incentive is wrong, but you then end up with a massive biodiversity value.”
While ecosystems right at the edge of the water have gained plenty of research interest, there’s much less information about the organisms that live further afield, in the continental shelf. Continental shelves, up to 200 metres deep, account for about 7% of the surface area of the oceans. The Zealandia continent that you may have heard about, stretching to the southwest and northeast of Aotearoa’s landmass, is a continental shelf. “We need numbers – to know the impact of trawling, to ground truth the models about how much carbon this ecosystem could absorb,” says Harris.
It’s not as simple as fish in = carbon stored, of course. I join Mara Fischer, an Exeter PhD student with curly hair tucked in a Convex Seascape Survey cap, on the top deck of Te Kaihōpara. She’s assembling BRUVS, Baited Remote Underwater Video Systems. Made of carbon fiber for lightness, the machines are simple four legged frames with slots for two GoPro cameras which are tilted and calibrated to help the researchers figure out how big the fish that swim past are.
Fischer’s PhD focuses on fish and carbon. “When the fish die, some of them will be eaten by other organisms – some of that carbon will end up in the atmosphere,” she explains as she sprays lanolin around the edges of the GoPro housing. At the sampling site, four BRUVS are dropped into the water, marked with a buoy (another ungainly process requiring lots of teamwork and hanging off the edge of the boat) and left for an hour.
Once the video footage is analysed, she’ll have data that can associate whether an area is protected, how much carbon is in the sediment and the size and variety of fish in the area. “The BRUVS are less invasive, the fish aren’t scared of them, they’ll come up to it to check out the smell,” she says, shaking a handful of chopped pilchard into a bait box with holes that is attached to the BRUVS.
Paolo Cortlezzi, a PhD student from the University of Western Australia who has been helping on the boat for a week, says he fell in love with the ocean as a child. Though he lived in inland Italy, he would visit his grandfather on the coast each summer. “I was snorkelling, I was getting the clams for making spaghetti,” he says, screwing a leg onto one of the BRUVS.
After getting a Masters in shark conservation in South Africa (he’s wearing a t-shirt with diagrams of South African fish), his supervisor convinced him that there were enough people working on sharks already, so he took a sidestep to learn more about soft sediment systems. His supervisor is good friends with a researcher on the Convex Seascape project, which is how he’s ended up in Aotearoa helping out; he’s studying similar areas off the coast of Western Australia.
“The ocean is like a big forest,” he says. “On land you have trees and all the plants that absorb carbon dioxide, in the sea you have microalgae or phytoplankton, they accumulate organic carbon in their tissue, and it’s transferred along the food chain.” The carbon part is simple. “Fish are made of carbon,” he says. “Through their life they produce carbon through feces, and when it dies, it sinks to the seafloor.” Fish poo sinks quite fast, so not much of it gets eaten by other creatures, and more is sequestered. Fish bodies may sink slower, with organisms nibbling and digesting it, but eventually some of that carbon will remain in the mud, too. Fishing interrupts this process. “You’re not just pulling the fish out, you’re transferring the carbon from the ocean to your dinner place. And when it’s on your dinner plate, it will end up in the atmosphere.”
On the boat, the question of how to quantify blue carbon could just be an academic one. There’s the rhythm of deploying different devices to encounter the seafloor, the arc of the wake of the boat, Fischer’s water-stained notebook an archive of what happens at each of the 14 sampling sites. But while the science might be methodical, what the scientists discover has political implications for the burgeoning game of carbon credits in a world where many of Earth’s “vital signs” are nearing record extremes.
Soft sediment is often a “hard sell” to protect, in Harris’s experience. It’s easy to get people excited about coral reefs or waving forests of kelp, but mud, deeper underwater than most humans will ever go? Part of the problem is that there are lots of questions around how biodiverse these parts of the ocean were before mass bottom trawling.
In areas like the Hauraki Gulf, which have been trawled for decades, many people have grown up around an ocean that has already been heavily degraded. What might have lived in the sediment before heavy trawl lines flattened seamounts and pulled out any creature big enough to get jammed in the net? With trawling nets able to shift even big boulders, this can lead to less habitat, fewer nooks and crannies for living things to dwell in. “You could trawl somewhere and leave it alone for 40 years, but it’s 100 metres deep, and it could take a century to develop that regenerative ecosystem,” Harris says. “Then you go out and look at it like, it’s fine to [trawl here], there’s nothing really living anyway – but your whole baseline has shifted massively.”
Part of the Convex Seascape Survey is piecing together historical data, which the sediment cores will help with, to get a sense of what the silty area under the sea could have been like before industrial scale fishing. This is something New Zealand scientists are researching too. It’s estimated that more than two billion tonnes of carbon are in New Zealand’s seafloor, especially in Fiordland. However, given that these ecosystems were part of the carbon cycle before humans released huge amounts of additional carbon into the atmosphere, simply conserving these areas isn’t enough. “We should just be reducing emissions as much as we can,” Harris says.
Human activity has already transformed the ocean, mostly for the worse. The water is contaminated; when Harris was doing his PhD in Wellington, looking at sea sponges in Wellington Harbour, he remembers colleagues finding kangaroo DNA in the water, thanks to kangaroo meat being used in dog food. He’s spotted microplastics in some of their samples, too, which might change the hydrocarbon readings. Biodiversity in the Hauraki Gulf is collapsing, snapper are starving, caulerpa is invading and mass death of fish, shellfish and seabirds will become more common thanks to climate change. Further marine heatwaves are expected this summer: from wriggling little nematodes to crabs scampering across the sediment to muscular kingfish, more heat will put vital species under further stress.
Out on the rippling ocean, though, the bulk of Te Hauturu-o-Toi on the horizon, the reality of climate change doesn’t feel like only doom and catastrophe. Instead, there is work to do. Williams neatly labels scoops of mud for lab analysis then sits at the side of the boat to manage the cable for the underwater vehicle Harris is operating. Cortelezzi and Fischer plop small snails scooped out of obscurity on the seafloor into ethanol, so they can be identified later. Caiger, a fish expert, coils lengths of ropes neatly into buckets.
And then, in mid-afternoon, a flurry. A pod of around a hundred dolphins ripple through the water, their tummies striped yellow and white, smaller babies propelling themselves next to their mothers, their chirping chatter audible even above the water. The sea ahead is rippled, a big group of fish clustered under the water. Matte sooty shearwaters flap hopefully on the surface; gannets drop like needles towards their prey. Far below is the soft silt of the sea floor, where all these fish will go one day if they don’t get caught or eaten. In the dolphins and birds, fish and crabs, all the micro-organisms that most of us will never see, the systems of carbon and life are utterly interconnected. Humans just need to find the right reason to protect them.
