Dense crayweed forests can be found on shallow reefs from Port Macquarie to Tasmania, but in 2008 researchers noticed a 70km gap along Sydney’s coast.

Most of our impact on the world around us isn’t immediate. It can take years, sometimes decades, to understand how dynamic and adaptable ecosystems eventually succumb to our bullshit. Or in the case of crayweed, human shit.

It seems hard to believe, but less than 40 years ago we were still pumping sewerage into the ocean just off Sydney’s beaches, and we weren’t doing a good job of treating it either.

Nowadays we’re doing a much better job with our human waste; in the 90s we started treating it properly and releasing it in deep water kilometres offshore. As a result, water quality on our beaches has drastically improved

But a 2008 study showed that crayweed, Phyllospora comosa, disappeared during this period of high pollution, and it never came back. 


Missing: Crayweed
Last seen: coastal reefs around Sydney in the 80s


‘So what?’ You might be thinking. ‘Who cares about a bunch of seaweed?’ The short answer? Every other critter in the ocean, many of which disappeared along with the crayweed, and you, if you love seeing wildlife in the ocean, eating seafood, or simply enjoying a coastline that’s as clean and healthy as can be.

But how do we get the crayweed back? Can we?

Proving That Crayweed Can Be Brought Back

Crayweed was still thriving up and down the coast, and the water quality in Sydney was much improved, so scientists began to wonder ‘Can we bring the crayweed back?’.

Research funded by NSW Environmental Trust and the Recreational Fishing Trust proved that they could, but it’s not as simple as planting a tree!

Phyllospora comosa attaches to shallow reefs with a structure resembling a root known as a ‘holdfast’. These holdfasts don’t reattach, so you can’t simply yank them off rocks up or down the coast and transplant them to Sydney.


Holdfasts strongly attach crayweed to coastal rocks, helping them resist heavy waves


Instead, researchers scuba dive to the ocean floor and attach a marine grade plastic mesh to bare rocks with a drill. They then secure transplanted crayweed to the mesh and wait for…

Lots and Lots of Seaweed Sex

It’s lucky that’s not the end of the story, because attaching a bunch of crayweed to rocks whilst diving underwater would cost a phenomenal amount of money and take forever.

Instead, researchers are all about reproduction. The motion of the ocean, if you will.


It’s a bit more complex than planting trees, but luckily crayweed reproduces rapidly!


When crayweed is removed from healthy ecosystems in Wollongong and the Central Coast to be brought to Sydney it (to use a scientific term) ‘freaks out’. Once it’s placed back in the ocean the totally-like-stressed-out crayweed thinks it’s going to die and begins trying to reproduce, hard.

It’s been shown that rates of reproduction are up to ten times higher at these transplant sites. Nice. Crayweed can actually be male or female, so it’s important to get a good mix, and their resulting babies can end up hundreds of metres from their parents, permanently attached to the reef. Pretty good news if you’re trying to make an underwater forest!


These plots rapidly produce more crayweeds that organically bond to the reef


Surprisingly, transplanted crayweed doesn’t die any quicker than crayweed that’s left alone in its habitat. Once it does die off (leaving behind a massive family), researchers come back and remove the mesh so that all that remains is crayweed naturally attached to the reef.

Operation Crayweed

The method’s been finessed and now involves planting 20m² of crayweed over a series of plots across a site. The entire site then fills out naturally over time with the spawn.

This happens pretty rapidly! Within two and a half years researchers have seen sites grow to about 400m² of crayweed, and 4,000m² within six!

All these findings and potential inspired the formation of Operation Crayweed, a group of scientists from UNSW, University of Sydney, and Sydney Institute of Marine Science as well as as volunteers who are passionate about bringing crayweed back to all 70km of Sydney’s coastline.

The Underwater Forest Project is We Are Explorers’ crowdfunding effort to raise $42,000 for Operation Crayweed so that they can plant out an entire site. Get involved!

Who cares about a bunch of seaweed?

Despite its rapid growth potential, 70km is a whole lotta coastline, so what are the benefits for bringing these underwater forests back to Sydney’s beaches and reefs?

Crayweed, or Phyllospora comosa, is unique, and supports a range of organisms and ecosystem functions that other seaweeds simply can’t. If it didn’t, crayweed could be called ‘ecologically redundant’, which apart from being a sick burn, would actually make it harder to justify replanting.

But researchers keep finding new ways that crayweed is important to Sydney’s coastal ecosystem. From feeding organisms that decompose organic matter on the sea floor (and go on to contribute to the food webs of important fish species), to supporting 7-10 times higher abundances of abalone or even hosting specific microbe diversity on its surface, crayweed is showing its value to the ecosystem.


Crayweed forms an important part of Sydney’s coastal ecosystem. Without it, many other species decrease in abundance


More simply, crayweed is both a habitat and a food source for local marine life, and far more valuable to coastal reefs than the bare rocks it left behind. Oh and of course crayweed is also essentially an underwater tree, which means that as it grows, reproduces, and restablishes itself over 70km of Sydney’s coastline, it can drawdown carbon from the atmosphere.

The Underwater Forest Project

In 2019, We Are Explorers crowdfunded $30,000 to purchase and permanently protect a plot of land in the Daintree rainforest, and in 2020 we raised $40,000 to plant over 8,000 native trees in the Snowy Mountains

This year we’re taking the planting underwater. Our goal is to raise $42,000 from readers like you to allow Operation Crayweed to plant out an entire site. We love the vision and potential the project has to right one of the wrongs humans have inflicted on the planet and pave the way for future projects.

Donors will be eligible for cool perks from a bunch of great supporting brands too!


Get Involved!


Feature photo by Justin Gilligan

All other photos by John Turnbull

Sources via Operation Crayweed