Reading Time: 6 Minutes Print this page

Most of the bathers sprawled during sunny weekends along the seawall at the Fairy Bower ocean pool, in the coastal Sydney suburb of Manly, wouldn’t be aware of the life surviving below their dangling feet…or how it’s impacted by this concrete structure. The wall, built in the early 20th century, is a small example of the mostly cement edifices that have been built along, and out from, the world’s coastlines. Globally, an estimated 32, of seawalls, pontoons, pilings and marinas now stretch into the ocean from various locations. In Australia, where 85 per cent of the population famously lives within 50km of the sea and properties with water views are among the highest-priced real estate in the world, the impact is thought to be huge.

“More than 50 per cent of the Sydney Harbour shoreline has been modified by coastal ‘hardening’ through the building of constructions like seawalls and jetties,” Macquarie University coastal ecologist Professor Melanie Bishop says, offering one local example. “And that’s increasingly being driven by the need for stabilisation and protection of the coast. It’s a common occurrence around the world.”

Melanie and others began looking, almost two decades ago, at what impact the structures were having on coastal organisms. They found much evidence that the diversity of life associated with marine constructions was not only reduced, but also vastly altered in terms of composition. “The biodiversity was not the same as is usually found along the natural shoreline. It was often characterised by more pest species and non-native species,” Melanie explains. “So we began researching why this was the case. And – alongside things like the difference in material type from which constructions are made versus natural rock type – one thing that really jumped out was that, if you walk along a natural rock platform at low tide, you notice all the life is found in places like rock pools, crevices and depressions. So the problem with these built structures is that they have flat, featureless surfaces.”

Looking for answers, Melanie and her team began small-scale experiments in Sydney Harbour and at about two dozen similar locations around the world. They found that if you add 3D geometries such as those seen along natural shorelines, the biodiversity of marine life around built structures could be increased and enhanced. Armed with that scientific evidence, the researchers approached Alex Goad – a Melbourne-based, award-winning industrial designer with a deep love for the ocean – to help find a solution. 

The result is Living Seawalls, a flagship program of the Sydney Institute of Marine Science that works in collaboration with Alex’s company, Reef Design Lab, to create marine life–friendly substrates that blend “ecological concepts and engineering in creative design”. Living Seawalls’ components are constructed from hexagonal concrete panels, each about 55cm in diameter, that mimic the lumps, bumps, nooks and crannies you’d see along a natural rocky shoreline. The modular design fits together like ceramic tiles.

“A key design criterion was that they be not only functional from an ecological perspective, but also look good,” Melanie says. “When you’re talking about public spaces, unless it’s an attractive solution, it’s not going to be palatable. So a big part of our success has been the ‘science meets art’ approach, and the fact that these things are visually appealing and sculptural.”

Living Seawalls’ panels were incorporated into recent renovations at the Fairy Bower ocean pool, and their surfaces are coming to life as algae and invertebrate larvae have been settling out of the water to grow on the structure. Seawalls like this have now been installed around the world at 20 different locations, including Gibraltar, Singapore, England, Wales and soon in Boston, in the USA. 

Fairy Bower ocean pool’s Living Seawalls – developed by the Sydney Institute of Marine Science – are concrete tiles made using 3D printers that mimic different types of habitat commonly found on natural shorelines. Image credit: Michaela Skovranova/Australian Geographic

The first Living Seawalls structure was installed in 2018 at Sawmillers Reserve, in the Sydney harbourside suburb of McMahons Point. Two years later a study found that 115 species of seaweeds and invertebrates had moved in to live on the panels. “There were 36 species of fish that were either feeding on what was growing on the panels, or sheltering in and around the panels,” Melanie says. “We are relying on natural colonisation – when all of the larvae and propagules [juveniles] floating around in the water settle and attach.”

The problem with the flat, featureless surfaces of old-school seawalls and jetties is that anything that settles on them is easily picked off and eaten by something bigger, or they’re exposed to the sun at low tide and killed by UV radiation. “The idea is that we’re providing protective spaces, these nooks and crannies, that allow species to survive,” Melanie says. “What we’ve found is that, in some instances, inside these rock pools and crevices, the temperatures are 10°C cooler than on an exposed surface. This can mean the difference between life and death for some of these species, particularly in a hot summer.”

With time, the invertebrates and seaweeds attach, survive and grow and then form their own habitats. “Initially, what you see is the sculptural design, but in time the panels are completely covered in marine life, so you can’t see the panels at all,” Melanie says. “You eventually get a lush self-sustaining marine habitat growing on top of them.”

A variety of marine organisms readily settle and grow in the  protected nooks and crannies on a Living Seawall, as pictured on this wall at Sawmillers Reserve, in the Sydney harbourside suburb of McMahons Point. Image credit: Leah Wood

The innovation in Living Seawalls is certainly about their nature-mimicking designs. But the material they’re made from is also important. They’re currently being fabricated using an ecoblend cement containing materials recycled from industrial waste products. “The hope is that, with so much innovation occurring in the materials space and in low-carbon and carbon-negative concrete, we will be able to use those innovations in our panels,” Melanie says. “That would really turn this into a carbon-negative solution. If we can build from low-carbon concrete, then encourage the growth of things like kelp that might be taking carbon dioxide out of the water, then we have a win-win solution.”

As the panels become covered with organisms, it seems they’ve been turning into their own self-perpetuating environment and won’t need any ongoing maintenance. “From an engineering perspective, the panels were initially designed so that they would last for at least 20 years in a harbour environment that’s exposed to sun, wind, waves and ferry wake, but we now think that’s massively conservative. As the creatures colonise, they are actually reinforcing the panels.” Another serious environmental issue for which the Living Seawalls project might offer a solution relates to the booming “blue economy” presently underway world-wide, partly driven by the quest for more renewable energy generation. Projects involving developments such as wind energy and aquaculture are being built in the ocean. 

“We are projecting that, if you combine everything – seawalls and coastal protection structures, along with new blue-economy offshore infrastructure and construction – that over the next 10 years we are going to see a 70 per cent increase globally in the area of sea floor impacted by the structures,” Melanie says. “What we are already seeing when we add it all up is an area of sea floor being impacted that is greater than the area occupied by the world’s seagrass beds and mangroves combined. It’s a significant issue and it’s growing, and the ideal time to combat this is not as an afterthought, but at the beginning.” 

As a result, the Living Seawalls team is now having conversations with a variety of offshore and coastal industries about how its innovative design solutions can be incorporated in marine construction projects from the very start.

Related: Two year study shows living seawalls promote regeneration in Sydney Harbour