Could such mimics help to limit the impact of climate change? Matteo Nannini

Tiny, artificial algae are being deployed in the first such effort to restore reefs in the Mediterranean Sea.

They look like coralline algae, which have a similar ecological function to corals: forming reefs using calcium carbonate structures that create diverse and complex environments.

“Coralline algae are particularly ecologically important in shallow, temperate regions,” says Federica Ragazzola at the University of Portsmouth, UK. They are ecosystem engineers, providing habitats for numerous small invertebrates and shelter from physical stresses such as wave action, because coralline algae live in exposed areas.


However, as the reefs they build are made from a soluble form of calcium carbonate, they are vulnerable to an ongoing ocean acidification.

So Ragazzola partnered with researchers from the Italian National Agency for New Technologies, Energy and Sustainable Economic Development (ENEA) to explore whether artificial coralline algae reefs can protect the organisms living on them against ocean acidification, as well as acting as scaffolds for natural coralline algae reefs to grow.

Rubber fronds

The team developed small plastic structures to mimic the natural coralline algae Ellisolandia elongata and the way it moves. The 90 synthetic mini reefs each with 20 fronds made of a highly elastic rubber material, known as silicone elastomer, were anchored in clear resin.

“The material was chosen to match the property of the algae and, more importantly, is non-toxic to the marine environment,” Ragazzola says.

These “mimics” were last month cemented close to existing coralline algae reefs in the Gulf of La Spezia, in north-west Italy.

Each is just 10 centimetres in diameter, so they can be easily nestled in the middle of a natural reef to encourage small organisms such as crustaceans, mussels and worms to move to the mimics.

The mimics will now be monitored to see if they are able to host these creatures.

Signs of colonisation

After just one month, the researchers are seeing signs that biofilms – thin layers of viscous fluid produced by and containing bacteria and microalgae – have already formed on some of the artificial reefs, suggesting microorganisms are beginning to colonise them.

And the progress could be rapid. “After a year, you should start to see some of the species – crustaceans and worms as well as microorganisms invisible to the naked eye – establishing on the mimics, as well as the start of the covering of coralline algae,” says Ragazzola.

If the artificial reefs do act as a scaffold for coralline algae to build structures on, this will provide new protective habitats for organisms and help fight ocean acidification.

“Coralline algae bioconstructions belong to these groups of organism that may play an important role in buffering the pH decrease, thus creating a microenvironment that may help some species to resist future climate changes,” says Ragazzola.

As waters become more acidic, coralline algae reefs will slowly dissolve, increasing the pH inside the reef, which might protect organisms living there from ocean acidification, she explains. The carbonate minerals made by the algae may act as the sea’s “anti-acid tablet” to increase the alkalinity of the seawater.

Even if the calcium carbonate structures built by the algae dissolve completely, artificial fronds could offer the algae a habitat, in turn supporting creatures higher up in the food chain.

Acid test

In 11 months, the researchers will take some of the artificial reefs and associated animals into the lab to study the effects of rising acidity on their health. They will be exposed to climate change scenarios projected for 2100 by the IPCC.

This will clarify how the coralline algae reef might act as a buffer to help maintain animal diversity and abundance, says Chiara Lombardi of the ENEA. “Our results will be important for the planning of future protection,” she says.

In the long run, the team expects to be able to make artificial reefs from biodegradable plastic that would gradually disappear, leaving only natural coralline structures in place.

The researchers hope small marinas could be lined with “fringes” of biodegradable artificial reefs to provide habitats for creatures, particularly in areas previously damaged by pollution. However, in the event of severe acidification destroying carbonate reefs, a more permanent plastic structure may be required.

They say that as coralline reefs are found all over the world, the idea could also be used in different regions and the artificial fronds adapted to suit local species.

“The concept of artificial reefs is well established as an approach to enhance biodiversity. This project seeks to further this approach to specifically regenerate coralline algae reefs,” says Aditee Mitra of Swansea University, UK.

“Some may see the whole concept of deliberately introducing plastics in the ocean in this way as contrary to the wish to promote well-being of marine life through removal of plastics, but the project will provide useful material for experiments,” she says.

Correction: The artificial reefs are made from silicone elastomer