These algae have been adapting for hundreds of millions of years

Like a dark shadow beneath the surface, kelp forests spread across the seabed. Newly hatched fish dart around among the swaying fronds. 

On the sturdy kelp stalks grow bryozoans, cnidarians, and other peculiar creatures.

Brown algae play a unique role in Earth's ecosystems. They perform photosynthesis, and capture megatons of carbon annually – like the vast forests on land.

Not plants, not animals

They are also foundational to coastal ecosystems. In some kelp forests, animal life reaches over 100,000 individuals per square metre.

Professor Galice Hoarau is reluctant to call brown algae plants – they are too distantly related. 

However, as vegetation, brown algae can be found all over the globe. Among all marine algae, brown algae dominate.

“When we talk about marine forests, it’s about brown algae. Most of the seaweed you see on rocks along the shore is brown algae. They provide habitats for other species, extract nutrients from the water, and offer physical protection by dampening currents and waves. They play a very important role,” says Hoarau.

An international effort

Researchers from 35 different research institutions and universities worldwide, including Nord University, have now collaborated to map the genes of brown algae. 

The genomes of more than 40 species from 16 different families have been mapped. A genome is the total amount of genetic material in a cell.

For researcher Ananya Khatei, this has opened new doors for research.

“Finally, the genes of the algae have entered the public domain. We can now begin to explore how the genome is organised and how the genes are regulated. These algae have experienced several periods of climate change, and we can now study how they developed the ability to adapt,” says Khatei.

A glimpse into the future

Khatei is doing research on epigenetics, the molecular mechanisms that turn genes on and off. One common mechanism is methylation, where the chemical compound methyl attaches to the DNA molecule.

She has found that DNA, the very code within the genes, is strongly influenced by the type and degree of such methylation.

“This indeed plays a huge role in the evolution of organisms. So the DNA we see today not only tells us the past story of how it was shaped, but predicts how epigenetics is going to shape it up in future along with the change in environmental conditions,” she says. 

Researchers can now trace changes in genes when a new branch of species emerges and link these changes to shared physical traits within that branch.

“For example, the development of alginate production is a shared trait among several species. Similarly, the development of what we call plasmodesmata – a channel system in the cell wall that allows cell communication – is another,” says Hoarau.

Alginate is used as a thickening agent in various food products.

Adapted while most others went extinct

The development of plasmodesmata  has been crucial in the evolution of multicellular organisms. It allowed brown algae to grow large, with different parts of the algae body taking on specialised functions.

“Remember, they live in tidal zones with strong currents and waves. Some kelp species can grow 15–20 metres tall,” says Hoarau.

Over time, the algae have developed specialised cells to anchor themselves to the substate.

This is an evolutionary milestone researchers date to 250 million years ago. It coincides with one of Earth’s largest mass extinctions, when 83 per cent of the world's species went extinct.

Approximately 50 million years later, as the supercontinent Pangaea broke apart and today’s oceans formed, brown algae developed a life cycle system where they alternate between different body forms from one stage to the next.

Researchers believe this period also saw the emergence of the large kelp forests. The ability of Norwegian brown algae to withstand drying out during low tide developed around 100 million years ago.

'Remember' stress across generations

Now, centuries of evolution and adaptation may be wiped out by climate change. 

Brown algae are cold-water species. They struggle when exposed to high temperatures for extended periods. Marine heatwaves can be devastating for them.

But it is also possible that they will once again manage to adapt. 

Alexander Jüterbock researches how algae adapt to warmer environments.

“We see that brown algae have an ability to ‘remember’ the stress they have been exposed to, allowing them to better withstand it when they encounter it again. It can be compared to a form of vaccination, where this ‘memory’ can be transferred from one generation to the next,” he explains.

He believes the answer to which molecular mechanisms are behind this lies in the epigenome.

“Brown algae differ significantly from plants and animals. Evolution has taken a completely different path. Brown algae have different enzymes that regulate genes, determining which genes to be turned on or off,” says Jüterbock.

A vital tool for conservation

The results of the study have provided researchers with entirely new tools to study and protect these algae. 

“Genetic diversity is crucial for species to adapt to a changing environment. That’s why it’s important to know if we have genetically unique populations or those with low diversity. Losing a population with high diversity also means losing the potential for adaptation,” says Hoarau.

Understanding their genetics is also essential for the growing algae industry. Brown algae are harvested for medical use and food production. More voices are calling for industrial cultivation of brown algae.

“Having a complete overview of the genome is a significant advantage,” says Hoarau.

Reference:

Denoeud et al. Evolutionary genomics of the emergence of brown algae as key components of coastal ecosystems, Cell, vol. 187, 2024. DOI: 10.1016/j.cell.2024.10.049

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Read the Norwegian version of this article at forskning.no

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