By Carrie Cox

UWA marine ecologist Professor Thomas Wernberg has devoted much of his professional life to making a squeaky wheel out of the Great Southern Reef – the interconnected system of temperate reefs hugging the bottom half of Australia and home to kelp forests that support the most unique temperate marine biodiversity on Earth.

Though decades behind the better-known Great Barrier Reef in terms of public awareness and resourcing, the Great Southern Reef is at last being recognised for the vital – and increasingly threatened – role it plays in biodiversity, ecosystem services and climate change mitigation.

UWA research has been critical to that shift. In fact, the very concept and name ‘Great Southern Reef’ grew out of the work of UWA scientists, desperate for the world to know just how unique and important this networked ecosystem is.

Image: Professor Thomas Wernberg.

“The Great Southern Reef has finally become a recognised entity and that signals to me that people are now taking on board the fact there is something out there that is unique and worthy of an identity and protection,” Professor Wernberg says.

“In Australia, the amount we’ve invested historically in understanding these kelp forests is less than 10 per cent of what we’ve invested in understanding coral reefs, even though kelp forests contribute twice the value in terms of ecosystem services. Hopefully that’s now starting to change.”

Kelp forests are fast-growing capturers of underwater carbon, just as efficient as tropical rainforests are in capturing atmospheric carbon.

In groundbreaking research published in July 2023 by UWA, researchers found that the climate benefits of seaweed forests have been grossly underestimated – the preservation and restoration of them could allow for the capture of millions of tonnes of carbon dioxide annually.

“Kelp are some of the most productive plants on the planet,” Professor Wernberg says. “They take up a lot of carbon dioxide and turn it into seaweed biomass very quickly.

"When storms come in and as the plants age, the kelp breaks off and is exported, much of it ending up in the deep sea where can be sequestered.”

But just as kelp forests help mitigate climate change, they are also threatened by it – a complicated loop that is central to Professor Wernberg’s current research.

“There’s no question in my mind that there is a feedback loop where more kelp buffers climate change, but the question is how big that loop is and whether there is anything we can do to break it,” Professor Wernberg says.

“Because if we want to mitigate climate change, we need to not just maintain these forests but actually increase them. If we simply maintain them, they’ll keep doing what they’ve always done. Increasing kelp forest areas will increase the amount of carbon dioxide that gets sequestered.”

Threats to the world’s kelp forests

Sixty per cent of the world’s kelp forests have been in decline over the past 50 years due to a variety of direct and indirect factors. A significant and direct threat in many regions of the world is the overfishing of lobsters, fish and other marine species that eat sea urchins. A major sea urchin outbreak can quickly devour a kelp forest.

More pervasive, and much harder to measure and simply halt, is the impact on kelp of climate change, specifically in terms of ocean warming and marine heatwaves.

“Put simply, you can just stop fishing and the problem goes away,” says Professor Wernberg, “but many of the impacts of climate change are often not direct and they’re very complex.

"When the temperature changes, everything biological changes. For example, the metabolism of species goes up and suddenly organisms have to eat more to stay alive.

"Shifting ocean currents also influence temperature changes and can cause an invasion of tropical species that over-graze kelp forests.”

A phenomenon known as ‘coastal darkening’ is yet another threat to thriving kelp forests. A multitude of factors can cause the light environment of the sea to dim – run-off from cleared forests on the land and nitrogen released from agriculture and sewage among them – and kelp forests will quickly suffocate in the new blackness.

Warming also exacerbates the negative effects of low light because the kelp needs more energy in warmer water.

The race for solutions

For many years, the research of Professor Wernberg and his team was focused on “mapping calamities” and understanding the extent of the problems plaguing kelp forest survival.

In recent years, he’s actively shifted his attention to a more solutions-oriented approach.

“Part of our research is still focused on quantifying the rate at which kelp forests have been, and are being, lost globally, but we’re also now increasingly focused on what we can actually do to make a difference,” Professor Wernberg says.

“So in addition to raising the profile of kelp forests and helping people appreciate their importance, we’re also trying to get a better understanding of the position of kelp forests in the carbon cycle, which is core to the question of to what extent can kelp forests help mitigate climate change.”

While Professor Wernberg’s team has already published research to show that kelp forests do take out more carbon than they produce, the big question remains of how much kelp is actually sequestered or locked away from the atmosphere for extended periods of time.

“In contrast to mangroves, salt marshes and seagrasses, kelp grows on rocks not sediment, so when a seagrass meadow captures carbon, it stores some of it locally, buried in the sediment where you can measure it, but you can’t do that with kelp because most of it is exported away from where it is produced and often ends up in the deep sea. Quantifying how much of it ends up there is what our current research is all about.”

‘Restoration is just a little Bandaid’

While research into the restoration of kelp forests is important and ongoing, Professor Wernberg and his team are measured about the reach of its benefits.

“Even if we are working on ways to scale up our efforts, we’re only doing it at a very small scale,” he explains, “yet the scale of loss is ginormous.

"Globally, at the scale we are doing it now, we need 200 million new kelp restoration projects every year just to match the current rate of loss, so we’re not even close. While very important locally, in the bigger scheme of things restoration is just a little Bandaid.

“Importantly, no measure of restoration can stop climate change – only limiting carbon emissions will. We need to treat the cause not the symptom”.

That said, there are benefits to understanding how kelp forests adapt to new environments and high temperatures.

“Restoration may be futile if we simply try to bring back what was already lost; what we plant today will be lost the day after tomorrow when the next marine heatwave comes in,” Professor Wernberg says.

“We need to restore to future environments and build resilience to what it will like in 100 years from now.

“For example, the kelp growing on reefs off Geraldton today can survive temperatures predicted for the south coast in 100 years’ time”, so if we can get those kelps to grow successfully on the south coast – before they are lost from Geraldton – we may just future-proof the Great Southern Reef get ahead of the climate change curve.”