Heat is destroying Australia's underwater forests. Seaweed biobanks could help save them

Heat is destroying Australia’s underwater forests, which are not made of coral but of seaweed. Stretching over 8,000 kilometers (5,000 miles) around southern Australia, these vast seaweed forests form the backbone of one of the world’s most diverse marine ecosystems. Home to seadragons, rock lobsters, giant cuttlefish, and southern blue devils, these underwater landscapes host more than 1,500 seaweed species and contribute significantly to the national economy. However, rising ocean temperatures and increasingly frequent marine heatwaves are threatening their existence. These sudden temperature spikes push seaweed beyond their survival thresholds, leading to widespread declines in their populations.

The impact of these environmental changes is profound. Seaweed forests play a crucial role in marine biodiversity, providing habitat, shelter, and sustenance for countless species. They also support vital fisheries, such as those for lobster and abalone. When entire populations of seaweed are lost, so too is the genetic diversity they carry. Genetic diversity allows species to adapt to changing conditions, such as increased heat tolerance. Without it, the resilience of these ecosystems diminishes, making them more vulnerable to future stressors.

One particular species, the golden-brown crayweed (Phyllospora comosa), has become central to efforts aimed at preserving these underwater forests. Once abundant along Sydney’s coastlines, crayweed populations declined sharply in the 1980s, likely due to sewage pollution. Despite improvements in water quality, the species did not naturally recover. In response, scientists initiated "Operation Crayweed" in 2007, working alongside divers to replant crayweed along Sydney’s shores. Over the past decade, this effort has successfully restored self-sustaining populations, including the establishment of Australia’s first officially named seaweed forest, Yanggaa Forest at Coogee Beach.

However, the success of restoration projects alone may not be sufficient in the face of ongoing climate change. Recent studies indicate that different crayweed populations possess distinct genetic traits, some of which seem to confer greater resistance to heat. Scientists suggest that using germlings—baby seaweed—from these resilient individuals to bolster vulnerable populations could enhance their chances of survival. This approach underscores the importance of maintaining genetic diversity within seaweed species to ensure their long-term viability.

Efforts to preserve seaweed genetic diversity are drawing inspiration from terrestrial conservation practices. Seed banks have been used for decades to store the genetic material of land-based plants, ensuring their survival for future use. Similarly, some kelp species can be conserved in biobanks, where microscopic forms called gametophytes are maintained in laboratory settings. These methods have supported global research, aquaculture, and restoration initiatives. Yet, the challenge lies in adapting these strategies to seaweed species that lack the microscopic life stages seen in kelp.

Unlike kelp, many dominant seaweed species in the Great Southern Reef belong to a group known as fucoids. Fucoids reproduce by releasing gametes—sperm and eggs—directly into seawater, where they fertilize and develop into germlings. This reproductive method complicates conservation efforts, as it lacks the stable, storable life stage present in kelp. Researchers are now exploring ways to apply cryopreservation techniques to these fucoid species, aiming to freeze and store their reproductive material at ultra-low temperatures. While initial attempts with crayweed show promise, further refinement of these techniques is needed to ensure their effectiveness.

As the threat of climate change continues to loom, scientists emphasize the urgency of developing robust conservation strategies for seaweed forests. The loss of these ecosystems would not only disrupt marine biodiversity but also impact the economic and ecological services they provide. By combining restoration efforts with innovative preservation technologies, researchers hope to safeguard these critical underwater habitats against the growing challenges posed by a warming planet.