Can degraded marine environments like Sydney Harbour be restored to a glittering seascape?

“Without exception, the finest harbour in the world.”

That is how Governor Arthur Phillip described Sydney Harbour when he first laid eyes on it in July 1788. Renowned Australian author Clive James echoed this sentiment, comparing the 30-kilometre-long estuary to a “crushed diamond”.

Sydney Harbour is also one of the most polluted and modified harbours in the world.

Phillip wasn’t thinking of the beauty of the harbour or its glittering reflections: “I have discovered the finest harbour in the world, where a thousand sail of the line may ride in full security,” and with that acknowledgement of the strategic security value of the harbour – rather than appreciation of its environmental value – came the problems.

Since the beginning of British colonisation, this tide-dominated, drowned-valley estuary – formed roughly 17,000 years ago when sea level rose, has had much of its natural value destroyed by pollution and the extensive development and industrial activity along its shore.

In fact, as well as being one of the most famous, research has shown that Sydney Harbour is also one of the most polluted and modified harbours in the world.

According to a 2014 report by the Sydney Institute of Marine Science (SIMS), more than 50 percent of its shoreline now comprises built structures such as sea walls, and almost 77 kilometres of the original 322 kilometres of shoreline has been reclaimed or infilled.

However, a major new scientific project is set to restore some of the critical habitat and biodiversity that has been lost in Sydney Harbour over the last 235 years. 

“Sydney Harbour is a modern, working harbour at the beating heart of our city, but the effects of urbanisation and industrial activity have resulted in the loss of marine habitats and the species that call them home.”

James Griffin

Project Restore is being delivered by SIMS, the NSW Department of Planning and Environment, Taronga Conservation Society Australia and NSW National Parks and Wildlife Service, and involves researchers from the University of Technology, University of New South Wales, University of Sydney and Macquarie University. It is being supported by the NSW Government with $4.5 million in funding committed through the NSW Environmental Trust and is the largest of three streams of the state government’s recently-launched Seabirds to Seascapes initiative.

“Sydney Harbour is a modern, working harbour at the beating heart of our city, but the effects of urbanisation and industrial activity have resulted in the loss of marine habitats and the species that call them home,” NSW Minister for Environment James Griffin said at the launch of Seabirds to Seascapes in August 2022. 

“While Sydney’s water quality has significantly improved in recent decades, so much so that we all delight at sightings of whales and seals in the Harbour, there’s no better time to supercharge our restoration efforts.”

The restoration of Sydney Harbour – home to approximately 3,000 marine plant and animal species, including over 600 species of fish, more than in the entire coast of New Zealand or England – is one of the largest projects of its kind in the world. It is also a very difficult one.

“Restoring underwater habitats is very different to restoring habitats on land,” Dr Martina Doblin, Director and CEO of SIMS says. “It’s much more challenging.”

Project Restore is underpinned by a multi-pronged approach to improving the overall health of Sydney Harbour. According to Doblin, one of the “anchor points” of the project is the enhancement and expansion of the Living Seawalls program throughout the harbour.

Restoring underwater habitats is very different to restoring habitats on land. It’s much more challenging.

Martina Doblin

Officially launched in 2018, drawing on two decades of research, Living Seawalls is one of SIMS’s flagship initiatives, in collaboration with Reef Design Lab. It involves installing 3D-printed modular habitat panels that mimic features of a natural shoreline, such as rockpools, crevices and hollows, onto existing man-made seawalls – and according to Doblin, “is a fantastic example of how building for nature and building for people makes sense.”

The aim is to transform existing man-made seawalls – which are usually smooth and flat and provide very little possibility for marine plants and animals to take hold – into microhabitats for a host of marine creatures. The research shows it’s working: after 1-2 years, the panels have been found to support at least 36% more species than conventional seawalls, with more than 80 species of invertebrates, seaweeds and fish living and growing on the heavy panels.

“This is similar to what we found on nearby natural rocky reefs, which are hotspots of biodiversity,” according to the team behind Living Seawalls, which won the 2022 Banksia Foundation Biodiversity Award.

The increase of marine life at these sites – especially of organisms like oysters which filter seawater – has additional environmental benefits. As Doblin explains: “When the filter feeding capacity at a site is increased, you see less particulate matter in the water column and an improvement of water quality.”

The panels have been installed at eleven different locations in Sydney Harbour, as well as in Queensland, South Australia, Western Australia, and internationally, including in Singapore, Gibraltar and Wales.

Hundreds more of the panels will be installed at sites in Sydney Harbour as part of Project Restore.

There was a time when vast amounts of seagrass and kelp could be found beneath Sydney’s sparkling waters. But most of this macroalgae has disappeared in the last fifty years.

“We’re still in the initial phase of the project…” Doblin says, “…which is to look at habitat suitability and whether local conditions are conducive to allowing marine life to grow and flourish.

“Instead of doing this randomly, we want to get better at restoration and learn more about the factors in the environment that lead to improved environmental outcomes.”

The benefits of enlivening seawalls at sites in Sydney Harbour will be augmented by another key aspect of Project Restore: the replanting of macroalgae, including seagrass meadows and kelp forests, which provide critical feeding grounds and shelter for a range of marine animals.

There was a time when vast amounts of seagrass and kelp could be found beneath Sydney’s sparkling waters. But most of this macroalgae has disappeared in the last fifty years – “largely because of nutrient pollution,” Doblin says.

One species of seaweed that will be a focus of the replanting efforts is crayweed (Phyllospora comosa).

A large brown macroalgae which forms dense forests on shallow rocky reefs, it supports a host of unique marine life – including lobster, abalone, bream and mulloway (and, helpfully, also captures carbon and produces oxygen.)

It once dominated the Sydney coastline but disappeared sometime in the 1980s – most likely due to the high volumes of poorly treated sewage that were pumped onto Sydney’s shores before deep ocean outfalls were constructed in the 1990s.

In recent years, SIMS has helped develop a method of restoring crayweed as part of Operation Crayweed. This method involves attaching healthy, fertile adult plants to biodegradable mesh nets, which are secured to bare, underwater rocks. The crayweed adults then begin to reproduce and their offspring form a new self-sustaining population. 

In addition to the replanting efforts, SIMS is working to address another major threat to seagrasses and seaweeds in the harbour: boat moorings.

“In their traditional configuration,” Doblin explains, “moorings have a heavy chain which scours the seafloor as the boat is swung around by the wind, and you get what’s known as mooring scars. In some areas, that can be quite significant: you can see circles around moorings of cleared seagrass habitat.”

An aim is to replace these traditional moorings with those which allow a boat to freely move but do not scour the seafloor.

Project Restore is due to be completed in 2025, and Doblin hopes that as well as improving the health of Sydney Harbour, it will have “an ongoing legacy of informing habitat restoration projects elsewhere in the world.” But, she adds, it will not fix all of the problems facing Sydney Harbour – chief among them being stormwater contamination.

“Every time it rains, contaminants are introduced to the harbour. That contamination can be directly harmful to humans and continues to build on the existing contamination in the harbour from past activities.”

“A marine park protected with sanctuaries, where no fishing is allowed, would be like a national park for protecting marine wildlife and habitats from the pressures our city brings.”

Danielle Ryan

According to Doblin, the fix to this problem involves treating or redirecting stormwater so that it doesn’t drain directly into the harbour. Although she acknowledges this is a “massive challenge” that “will need longer term work and coordinated action from many stakeholders.” But she believes it is possible.    

Others say even more needs to be done to help guarantee the success of Project Restore and further enhance Sydney Harbour’s health, such as the creation of a new Sydney Marine Park.

“A marine park protected with sanctuaries, where no fishing is allowed, would be like a national park for protecting marine wildlife and habitats from the pressures our city brings,” Australian Marine Conservation Society marine parks campaigner Danielle Ryan said.

Perhaps, then, Sydney Harbour is on its way to becoming – once again and without exception – the finest harbour in the world.

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