‘Coastal squeeze’: the fight to save shoreline habitats from rising tides

The rain has just stopped falling when Nigel George walks down to the beach in Sandown Bay on the Isle of Wight. He crosses the coastal road and descends a concrete stairway, a sheen of sand covering its lowest steps. The place is quiet, with only a few walkers animating the shoreline.

He’s here to inspect a wooden groyne – a kind of jetty, designed to prevent erosion – which stretches out into the sea and towards France. The groyne has been fitted with a series of small, basin-like, rough concrete, structures. George peers inside one: a congregation of limpets, barnacles, seaweed, and a single sea snail peer back at him.

It started slowly but is surely picking up speed: the ocean, long considered so big it couldn't be affected by humanity, is creeping toward us. As the water warms and the ice sheets melt, sea level has risen more than half a foot in the last century – and even if we stopped producing greenhouse gases today, a very unlikely scenario, it will only keep coming. With 40% of the Earth's population living in coastal zones, the UN has warned that the accelerating pace of sea level rise threatens a "mass exodus".

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This is what George’s organisation, Artecology, calls a “Vertipool – a vertical rockpool. It’s an artificial environment that provides safe shelter for sea life in intertidal habitats, the spaces between land and sea all around the world that are alternately exposed and then swamped by tides.

Developers and scientists have installed about 1,000 of these fake rockpools on hard coastal structures around the UK, in the hopes of fending off a new, global threat – a geographical process called “coastal squeeze”.

Coastal squeeze happens when, as global heating causes sea levels to rise, tidal low-water marks – the line where the tide stops and the mud and rocks are exposed – are forced farther inland. A World Meteorological Organisation report published last year indicated this is now happening twice as fast as it was in 1993.

Humans, meanwhile, are pushing in the opposite direction, by building more hard coastal structures such as sea walls to protect themselves from rising water and worsening storms. These structures prevent the tide’s high-water mark from moving inland – effectively “squeezing” or reducing the size of intertidal habitats.

The impact to date has been brutal on the wildlife that lives within these habitats, from barnacles and limpets to crabs, starfish and snails.

“Species that inhabit the intertidal zone have evolved to live in that environment,” said Pip Moore, a professor of marine science at Newcastle University. These animals find the world’s rising temperatures very stressful, she says. “Lots of organisms use the natural heterogeneity in the rocky shore to hide away from those stresses – [but] a seawall or even a “riprap” boulder don’t have that complexity of habitat.”

Exactly how badly coastal wildlife is affected by coastal squeeze is not entirely clear, but scientists have found that structures such as Artecology’s Vertipools show a “significantly greater” species richness when compared with a normal seawall after five years. One Bournemouth University team found species of crab, fish and periwinkle living in them that had been absent before.

“If you deploy these objects in the intertidal zone they can support life that you would expect to find on a horizontal plane,” George says.

Other organisations around the world have approached the problem in different ways. A Sydney company called Living Seawalls uses 3D printers to create reinforced concrete interlocking panels that mimic the features of rocky shorelines – some scored with deep crevices, others shaped like honeycomb. Developers have attached these “fake shoreline” panels to hard coastal structures in Australia, Singapore, Gibraltar and the UK.

But effects can vary. An Australian paper in June showed some of the Living Seawalls panel designs work better than others, with a rockpool-like design hosting more than 100 different species compared with a honeycomb structure that proved only marginally better than a flat panel used as a control.

Meanwhile, another project, called Marineff, dropped 12 “eco-engineered” breakwater blocks into the intertidal zone of Cherbourg harbour in France. Instead of the flat surfaces of standard breakwater blocks, Marineff’s were covered with crevices and holes to better support wildlife. They were formed with a concrete mix that contained 20% oyster shell, aiming to provide a ‘bio-mimetic’ surface for sea life to live on, according to the project director Pascal Claquin.

One of the biggest intertidal interventions to date is part of the US government’s Rebuild by Design project, launched in 2013 after Hurricane Sandy killed 24 people on Staten Island.

Instead of building a traditional breakwater to prevent future flooding, the project allocated $60m (£49m) for a six-kilometre “living breakwater”, including 600 concrete rockpools. Designed by a company called ECOncrete, these rockpools are a lot larger than Artecology’s, weighing about 1.4 tonnes each.

The company claims the incoming organisms that grow in the rockpools help to protect the breakwater itself. “They absorb wave and debris forces, so the actual concrete that’s contained within them is maintained for a much longer time,” says Andrew Rella, the project’s director at ECOncrete, which is based in Israel. “Really, we’re creating a barrier between the concrete element and the natural environment.” The firm has deployed similar concrete objects in the Netherlands, Hong Kong and the UAE.

Pouring such vast amounts of concrete has been criticised, given that cement contributes between 5-8% of the world’s CO2 emissions. Rella argues that ECOncrete only contributes to structures that would have used concrete anyway, and that the habitats help offset emissions by hosting wildlife that sequesters carbon.

Whether or not that’s true, such interventions are likely to increase as governments enact more ecological legislation. One major effort is the UK’s “biodiversity net gain” requirement, which will become mandatory late in 2023, that would force building developers to achieve a 10% overall biodiversity gain for new projects. It would require coastal developers to build structures that provide better habitats for intertidal wildlife, or compensate for damage elsewhere.

“Exactly how this will play out for all coastal developments, and in the future for offshore areas, is still being worked out – it’s still fairly new,” said Dr Kevin Linnane, an associate director at development consulting group RPS. He said that most developers supported the net gain policy.

Scientists are sceptical: one paper published in the journal Conservation Letters last year concluded that enforcement and governance would prove difficult. “Reconciling infrastructure expansion with biodiversity conservation is deeply challenging,” the authors wrote. “Even ambitious policies are subject to huge uncertainties that risk undermining their biodiversity benefits.”

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George believes a systemic change to how people view the natural world is the only long-term solution to intertidal habitat loss. Artecology wants to do that person by person, starting with the local community on the Isle of Wight. To that end, his team have run free daylong craft sessions at a local school for children with special needs, and a free two-day arts and science festival for families October. George is now in the early stages of creating an educational Centre for Flexible Learning and Bio-Innovation at Artecology’s studio.

“They need to understand what’s going on and why,” he said. “We’re not going to get the take-up we need when we don’t have the support of our communities and people.

“It’s as much about human beings as it is wildlife.”