'Ocean architects’ expose hidden threats of climate change

Bryozoans are tiny marine animals that live in colonies and quietly build underwater structures on which many species depend. These little invertebrates often go unnoticed, even though their work is essential to life in the sea. Now, research shows that climate change may be pushing them past their limit.

A recent study from scientists at the Institut de Ciències del Mar (ICM-CSIC) takes a close look at how ocean acidification and warming are affecting bryozoans.

The team focused on two species that play an important role in building marine habitats, including Myriapora truncata, also known as the “false coral.”

Bryozoans build marine homes

Myriapora truncata forms complex, three-dimensional structures that give shelter to a variety of marine life. These aren’t true corals, but they serve a similar purpose – building habitats that other species rely on.

The researchers examined how this species, along with another type of encrusting bryozoan, responds to future ocean conditions. These include warmer temperatures and more acidic water, both of which are caused by rising carbon dioxide levels in the atmosphere.

“Despite being a different phylum, very diverse and abundant globally, these small architects of the sea are often overlooked in studies,” said Blanca Figuerola, ICM-CSIC researcher and lead author of the study.

Figuerola noted that bryozoans play a very important ecological role and their microbiome had been virtually unexplored.

This study is the first to describe the microbiome – the community of microorganisms that live in and on these animals – of the false coral.

Volcano bubbles mimic future seas

To study how these organisms respond to acidified oceans, the research team used a unique spot off the island of Ischia in Italy. Natural volcanic bubbles mimic ocean acidification levels expected by the century’s end.

“This area offers a unique opportunity to study how marine species respond to acidification under natural conditions,” said Núria Teixidó, a researcher at the Stazione Zoologica Anton Dohrn and co-author of the article.

The scientists compared bryozoan colonies in acidified waters with those in normal conditions, examining their shape, skeleton structure, and microbiome.

The researchers found that the species show some flexibility. Animals in acidified water changed their skeleton composition in a way that could help them resist harsher conditions. And overall, their microbiomes stayed fairly stable – but not entirely.

Trouble in the microbial neighborhood

The study found that acidified conditions reduced the variety of microbes performing key functions inside the bryozoans.

“However, we observed a loss in functional microbial diversity, with a decline in genera potentially involved in key processes such as nutrition, defense, or resistance to environmental stress,” said Figuerola.

That shift could have serious consequences over time. Even if the bryozoans look fine on the outside, a weaker microbiome could leave them more vulnerable to disease.

“Even if colonies look externally healthy, changes in the microbiome could serve as early bioindicators of environmental stress,” said Javier del Campo, a researcher at the Institute of Evolutionary Biology (IBE, CSIC-UPF).

Double blow to reef-makers

Alongside acidification, the study also tracked the impact of rising ocean temperatures over a five-year period. When warming is added to the mix, the effects worsen.

“The models used indicate that the combination of these two stressors intensifies the effects observed, significantly reducing the coverage of the encrusting bryozoan and increasing mortality,” said Pol Capdevila, a researcher at the University of Barcelona.

“Although the species show some morphological plasticity, it is not enough to offset the combined impact of acidification and warming.”

To reach these findings, the team used advanced modeling techniques and micro-CT scans to get 3D images of the internal skeletons of these animals.

The team is currently working with Cooked Illustrations, a visual storytelling studio, to turn their research into a science animation aimed at education and outreach.

Bryozoans deserve more attention

Bryozoans may not get as much attention as corals, but they play a similar role in creating habitats for other marine life. If they start to disappear, many other species could be affected.

This study highlights how important it is to understand not just the animals themselves but also the microbes they live with.

By identifying potentially beneficial microorganisms, researchers are opening the door to future methods of helping these organisms adapt. These may include nature-based solutions that support both the host and its microbiome.

The research started under the MedCalRes National Plan project. It is continuing through the HOLOCHANGE consolidation project and the National Plan MedAcidWarm.

These initiatives aim to better understand how bryozoans and their microbiomes interact, and how we might help them cope with climate stress.

“The complexity of the issue demands integrated analyses,” said Figuerola. “This study shows how interdisciplinary approaches can help us anticipate future scenarios and more effectively protect marine ecosystems.”

The full study was published in the journal Communications Biology.

Image Credit: ICM-CSIC

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