Australia battles to protect its underwater forests

Australia’s underwater forests, known as the Great Southern Reef, stretch more than 8,000 km along the southern coast and support a diverse marine community.

Seaweed forests under pressure

Unlike coral reefs, the Great Southern Reef is built from seaweed, with more than 1,500 species forming dense, tall forests that sway in the current. The habitats shelter seadragons, rock lobsters, giant cuttlefish and southern blue devils, and they underpin fisheries that generate billions of dollars each year.

Rising ocean temperatures are eroding this foundation. Marine heatwaves—periods when water heats rapidly and stays warm—have already driven declines in seaweed cover across the country. When temperatures exceed the tolerance of cold‑water algae, the fronds die back, and the associated wildlife loses its home.

Genetic diversity as an insurance policy

Scientists argue that preserving the genetic variety within seaweed populations is essential for future resilience. Different populations carry unique genetic traits that may allow some individuals to survive higher temperatures. If a local population disappears, those traits are lost forever.

Restoration efforts and their limits

Restoration alone may not keep pace with warming seas. Recent studies show that separate crayweed populations hold distinct genetic profiles, and some individuals appear better equipped to tolerate heat. Planting germlings from these heat‑tolerant lines into vulnerable sites could boost survival odds, but the approach is still experimental.

From seed banks to cryobanks

Land‑based plants have long been safeguarded in seed banks, where dormant seeds can be revived when needed. Some kelp species are kept alive in biobanks as microscopic gametophytes, supporting research and aquaculture worldwide, including in Australia.

Most seaweeds dominating the Great Southern Reef belong to the fucoid group, which lacks a microscopic stage and releases sperm and eggs directly into the water. This reproductive mode makes conventional biobanking difficult.

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Scientists are turning to cryopreservation—freezing reproductive material at around –196 °C—to store genetic material from such species. The technique, familiar from assisted reproduction in humans and livestock, could also preserve fucoid algae.

In a recent trial, frozen crayweed sperm survived thawing, while germlings did not yet recover. They view the result as a proof of concept, noting that methods must be refined before they can be applied to a broader range of Australian seaweeds.

Building a broader strategy

Preserving genetic diversity through cryobanking could buy time for new conservation tools, such as assisted gene flow, where heat‑tolerant individuals are introduced into at‑risk populations. Australia already boasts a robust algal culture collection and is a world leader in coral cryobanking, providing a foundation for expanding seaweed cryobanking.

Developing effective protocols will require identifying which populations contain unique or threatened genes, assessing their vulnerability to climate change, and improving freezing and recovery techniques. Input from Indigenous custodians, government agencies, conservation groups and local communities will be essential in deciding which species and locations merit priority treatment.

It is important to stress that cryobanking does not replace habitat protection or address the root causes of warming oceans. Instead, it serves as an insurance policy for biodiversity, a way to retain the genetic toolkit that may be needed as conditions shift.

Looking ahead

Much of the Great Southern Reef’s seaweed has already been lost, and the window for action is narrowing. By combining restoration, genetic research, and cryopreservation, scientists hope to keep the underwater forests viable for future generations.

For more background on the reef’s ecological importance, see the Great Southern Reef Wikipedia entry.