Marine acidification, driven by global warming, threatens not only corals, the authentic builders of many ecosystems, but also a wide range of other calcifying organisms. Crustaceans, mollusks, and sea urchins rely on calcium carbonate for their shells and skeletons, and recent research suggests that rapid changes in ocean chemistry could outpace their ability to adapt.
A recent study led by the Institute of Marine Sciences (ICM-CSIC) with collaborators from the British Antarctic Survey, the Institute of Oceanology, the Polish Academy of Sciences, and the University of Gdańsk shows that warming and acidifying oceans jointly influence marine animals that rely on calcium carbonate structures. The study, published in a prominent journal, focuses on organisms with calcium carbonate skeletons across the Southern Ocean near Antarctica, where colder waters increase the solubility of calcium carbonate, making shell formation more difficult for these species.
Bryozoans, a key to understanding impact
To conduct the study, researchers examined the skeletons of bryozoans, small filter-feeding invertebrates that settle on the seafloor and can create complex habitats for many species. Like corals, bryozoans form calcium carbonate skeletons and often live in colonies, but they have a broader geographic distribution, particularly in Antarctic waters. Their varied mineralogy makes them excellent models for studying the effects of global change, as noted by Blanca Figuerola of ICM-CSIC, the study’s lead author.
Figuerola explains that bryozoan skeletons comprise two main carbonate minerals, calcite and aragonite, and may contain magnesium, which can heighten sensitivity to acidification. A co-author from the British Antarctic Survey adds that higher seawater temperatures correlate with a greater prevalence of species with magnesium-rich skeletons, hinting at broader vulnerability as oceans warm.
As Figuerola observes, species with high magnesium in their skeletons could face greater risks as temperatures rise. In the face of rapid climate shifts, these organisms may struggle to keep pace with changing conditions, underscoring the potential for wide-reaching ecological disruption in marine ecosystems.
The scale of the work was made possible through collaboration with members of an international bryozoology society, which expanded data on bryozoan mineralogy across a broad range of species from polar to tropical waters. This cooperation strengthens the ability to compare patterns and predict responses under future ocean scenarios.
The future of marine calcifiers
Rising CO2 levels are transforming oceans by boosting temperatures and altering seawater chemistry. When CO2 dissolves in seawater, it forms carbonic acid, which reduces the availability of carbonate ions essential for calcification. As a result, calcified organisms that rely on calcium and carbonate ions experience weaker skeletons in more acidic waters. The extent to which these organisms can adjust their skeletal chemistry in response to coupled changes in temperature and pH remains uncertain, as do the broader ecological consequences.
Looking ahead, Figuerola and collaborators plan to extend the research under the MedCalRes framework, investigating possible morphological, metabolic, and microbiome responses in calcifying organisms, including bryozoans and corals, facing ongoing ocean warming and acidification. This expanded effort aims to better understand how these species adapt or decline when faced with changing ocean conditions.
Reference work: https://onlinelibrary.wiley.com/doi/10.1111/ecog.06381
End of excerpt. The environmental science community continues to monitor shifts in marine calcifiers as temperatures rise and carbonate chemistry shifts, seeking insights into the resilience of key reef-building and habitat-forming organisms and the potential ripple effects across marine food webs.
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