Beneath the Mediterranean waves, tiny marine “architects” called bryozoans are showing alarming signs of stress as climate change drives both ocean warming and acidification.
Using volcanic CO2 vents as a natural preview of the future, scientists uncovered skeletal weakening, microbial shifts, and declining resilience in species like the “false coral,” which provides vital shelter for marine life.
Climate Change Threatens Bryozoans
A team from the Institut de Ciències del Mar (ICM-CSIC) has released findings in Communications Biology showing that ocean acidification and warming, two major results of global climate change, can at the same time alter the structure, mineral content, and microbiome of bryozoans. These colonial invertebrates are essential for creating marine habitats, and the results point toward potentially severe ecological impacts if climate change continues to accelerate.
“False Coral” Under the Microscope
For the first time, researchers have described the microbiome of Myriapora truncata, a habitat-forming species commonly called “false coral” that is widespread across the Mediterranean. The study also examined how this species, along with another encrusting bryozoan, might respond under projected future conditions. False coral colonies grow into three-dimensional frameworks that provide refuge for many marine organisms, much like other bryozoans that can even build reef-like systems, though corals usually receive far more scientific and public attention as ecosystem builders.
“Despite being a different phylum, very diverse and abundant globally, these small architects of the sea are often overlooked in studies on responses to environmental changes,” explains Blanca Figuerola, ICM-CSIC researcher and lead author. She highlights that this research offers new insight into how bryozoans could adapt, or fail to adapt, to the ocean’s rapid transformation.
Figuerola also points out that “bryozoans play a very important ecological role,” but until now, little was known about how they cope with the combined pressures of acidification and warming. She adds that “their microbiome had been virtually unexplored.”
Natural CO2 Vents as Research Sites
To conduct the study, the team used a “natural laboratory”: on the island of Ischia (Italy), volcanic CO2 bubbles from the seabed, which allow simulation of the ocean acidification conditions projected for the end of the century.
“This area offers a unique opportunity to study how marine species respond to acidification under natural conditions,” explains Núria Teixidó, researcher at the Stazione Zoologica Anton Dohrn and last author of the article.
Using this approach, the researchers compared the morphology, skeleton mineralogy, and microbiome of colonies of two bryozoan species exposed and unexposed to these conditions. Results show that the species exhibit some acclimation capacity, modifying their skeletal mineralogy to become more resistant and maintaining a relatively stable microbiome composition.
Microbial Shifts and Early Warnings
“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,” Figuerola states.
These microbial shifts may have important long-term consequences, since the microbiome plays a fundamental role in bryozoan health and resilience. “Even if colonies look externally healthy, changes in the microbiome could serve as early bioindicators of environmental stress,” adds Javier del Campo, researcher at the Institute of Evolutionary Biology (IBE, CSIC-UPF).
Warming Intensifies the Damage
Over a five-year monitoring period, the study also considered the effects of rising temperatures — another key factor in climate change.
“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. Although the species show some morphological plasticity, it is not enough to offset the combined impact of acidification and warming,” says Pol Capdevila, researcher at the University of Barcelona.
To reach these conclusions, the team used advanced techniques such as modelling and computed microtomography to obtain, for the first time, 3D images of the internal skeleton structure of these species. These images are valuable both for research and for science communication and environmental education. The team is currently preparing a science animation for the general and educational public, in collaboration with the team at Cooked Illustrations, a visual storytelling studio.
Conservation and Future Research Directions
The findings have important implications for the management and conservation of Mediterranean marine ecosystems, particularly in the context of climate change. Habitat-forming species like bryozoans are not only vulnerable but their disappearance could trigger cascading effects on many other species that rely on them for shelter or food.
The characterization of the microbiome and preliminary identification of potentially beneficial microorganisms open new research avenues to enhance the resilience of holobionts (host and its associated microbiome) through nature-based approaches.
This research line, initiated under the MedCalRes National Plan project, is now continuing with the HOLOCHANGE consolidation project and the National Plan MedAcidWarm, which aim to deepen understanding of bryozoan–microbiome interactions to anticipate and mitigate climate change impacts.
“The complexity of the issue demands integrated analyses,” concludes Figuerola. “This study shows how interdisciplinary approaches can help us anticipate future scenarios and more effectively protect marine ecosystems.”
Reference: “Interactive effects of ocean acidification and warming disrupt calcification and microbiome composition in bryozoans” by Blanca Figuerola, Pol Capdevila, Marc Cerdà-Domènech, Joaquim Garrabou, Alice Mirasole, Pol Bassols, Javier del Campo and Núria Teixidó, 31 July 2025, Communications Biology.
DOI: 10.1038/s42003-025-08524-8
Never miss a breakthrough: Join the SciTechDaily newsletter.
3 Comments
Scare tactics.
“…, the team used a ‘natural laboratory’: on the island of Ischia (Italy), volcanic CO2 bubbles from the seabed, which allow simulation of the ocean acidification conditions projected for the end of the century.”
When I first read this I thought that perhaps they were using the term “ocean acidification” correctly for a change. The water is almost certainly saturated with CO2. However, nowhere in this press release is the actual pH mentioned. One has to go to the DOI link to find the actual published paper. There, one discovers about half-way through the text, in “Methods,” that the nearby, average reference ambient pH is stated as 8.05 (essentially what is assumed for the open ocean), and their “low-pH” averages range from 7.65 to 7.88, both within the range chemists define as being basic or alkaline. They refer to “low-pH,” but that is only with respect to the nearby ‘ambient pH’, in the cave, not in the absolute range that is defined as being acidic. In that sense, the statements are misleading! The pH scale is bisected by the point of neutrality with a 1:1 ratio of hydronium and hydroxyl ions, and only the lower half of the scale (~ -1 to <7) is defined as acidic. The authors should have clarified that when they mentioned "low pH" they only meant lower than the reference ambient pH.
They mention that under the extreme, and demonstrated improbable, SSP5 RCP8.5 scenario, the predicted 2100 CE ocean surface pH would be <7.80, but NOT 7.65. Therefore, their conclusions are based on a situation that is improbable and thus not a good simulation of the future.
Their work actually suggests that under the most extreme conditions, water saturated with CO2 will only get to around a pH of 7.6 (basic) because of (bi)carbonate and borate buffering. Nobody is expecting the surface waters to become saturated with CO2! In the Bahamas, limy muds precipitate out because calcite becomes less soluble as water warms and CO2 out-gases.
Renowned Stanford geochemist Konrad Krauskopf states in his textbook that it is unlikely that the oceans will ever even reach neutrality, except in some stagnant bottom pools enriched in hydrogen sulfide. Perhaps the researchers should add a geochemist to their team, or at least the peer reviewers.
I’m impressed by the analytic detail the authors go into. They obviously have access to a well-funded laboratory with state of the art equipment and they have been tutored in how to use it.
However, if basic, critical assumptions are not examined and validated, all the collected data may well be meaningless. The most critical step in experiments like this is the design phase. That is the time that input should be solicited from experts in other fields, such as geochemistry. The difference between a technician and a scientist is the approach to dealing with questions and conclusions. Data are not compelling unless they have been examined with the detail and objectivity recommended by T. C. Chamberlain in his Method of Multiple Working Hypotheses:
https://www.science.org/doi/10.1126/science.148.3671.754