Seaweed cells could give solar panels a boost

Seaweeds are a vital part of ecosystems and diets around the world – and they could one day power your home.

Red seaweeds are among the oldest types of multicellular life on Earth, with their ancestors first appearing around 1.6 billion years ago. Over that time, they’ve evolved into many different forms, from calcified algae that looks like underwater lichen to longer and more flowing forms.

By learning lessons from the evolutionary journey of these seaweeds, scientists could find new ways to solve some of the world’s biggest issues. This area of research, known as biomimetics, has been applied to everything from butterflies to electric eels. Now it’s seaweed’s turn.

Margot Arnould-Pétré, one of our PhD students, was the lead author of a review looking at how the structural colours of seaweeds could lead to new discoveries. She said that seaweed biomimicry could help engineers in many different industries, including green energy.

“Most solar panels convert around a quarter of light they receive into electricity, which is good, but they could be more efficient,” Margot explains. “By mimicking the ways seaweeds can absorb and capture light, we might find new ways that these devices can be improved.”

“I can also imagine these properties of seaweeds inspiring ultraviolet-resistant fabrics, paints and other materials. Red seaweeds are able to use their cell structure and contents to protect themselves from the Sun, so studying these properties could present new avenues for biomimicry.”

The findings of the research were published in the Journal of the Royal Society Interface.

What gives red seaweeds their colour?

Despite their name, not all red algae are actually red. They can be a range of different colours, from greens and blues to purples and browns.

Part of the overall colour is due to the seaweed’s pigment, but the rest is down to its structure. Typically structural colour is caused by the way light interacts with an organism’s surface at a nanoscopic level, such as in the brilliant colourful feathers of many birds-of-paradise.

Red seaweeds are also known to have structural colours that produce iridescent effects, but this phenomenon hasn’t been well studied. Its fleeting nature and dependence on the right environmental conditions means that most scientists have noted it but not dug any deeper.

Margot and her co-authors decided to change that, looking back over more than a century of research to find out everything they could about structural colour in red seaweeds. They found two types of structural colour in red seaweeds, one which develops inside the organisms’ cells and another that forms on the outside.

“One of the types of structural colour is caused by nanostructured organelles,” Margot explains. “These are small intracellular structures packed inside the cell which can be spherical or more elongated depending on the seaweed.”

“These structures scatter light, producing different shades depending on how they are arranged. We’re not exactly sure how these evolved at the moment, but we’re hoping to find out more.”

The other type of structural colour they found sits in ‘multilayers’. Lower and higher density layers in the outer cuticle of seaweeds reflect and refract wavelengths of light and give the seaweed a metallic blue sheen.

You might have seen it for yourself in Irish moss, a type of seaweed found along the rocky Atlantic coasts of Europe and North America.

What does the colour of red seaweeds do?

Red seaweeds are using their structural colour for a variety of reasons that have helped them to adapt to life in the oceans.

One of the main uses is to protect themselves from excess sunlight. While seaweeds need a certain amount of sunlight to carry out photosynthesis, too much damages their cells and could kill them.

During the reproductive stage of Irish moss, for example, the structural colour on their outside helps to dissipate the higher energy wavelengths of light before it can penetrate inside their cells. This ensures that the seaweed’s DNA is protected so it can reproduce without passing on genetic damage to the next generation.

Other seaweeds, however, may do the opposite. Though experimental evidence is currently lacking, some research suggests that seaweeds living in low light environments might use their structural colour to funnel light directly to their cells to enhance their levels of photosynthesis.

The colours can also be used to ward off potential predators, as seems to be the case in Asparagopsis taxiformis. Blue tips on the seaweed are thought to be a warning of the noxious chemicals the seaweed contains, similar to how a poison dart frog or blue-ringed octopus advertise their deadly toxins.

Some red seaweeds, however, don’t have structural colour at all. Either these species lost the ability to produce structural colour, or that they never evolved it in the first place.

Answering these questions will mean getting a much clearer understanding of all seaweeds, not just the reds. Margot hopes that ongoing projects to support research into these algae will start to offer new possibilities for scientists.

“There’s still a lot we don’t know about seaweeds, and we need more people to look into them,” Margot says. “The taxonomy of many seaweed families is very uncertain, so it’s difficult to link their evolution to features such as structural colour at the moment.”

“However, there’s a lot of potential for new discoveries. We know that green seaweeds, for example, have very different mechanisms of structural colour than the reds. This could offer further ways of exploring biomimicry in these organisms.”