№ 126/2025 from Jul 22, 2025

A long-term study investigating the growth of corals in the Caribbean over the past century has shown that even stress-tolerant species of corals are finding it difficult to adapt to increasing ocean temperatures and other human-induced factors such as coastal pollution and overfishing. An international team of scientists led by researchers from Freie Universität Berlin has revealed a sobering reduction in coral calcification rates, a development that will have far-reaching consequences for marine and coastal ecosystems. Their study, “Emerging Skeletal Growth Responses of Siderastrea Siderea Corals to Multidecadal Anthropogenic Impacts in Martinique, Caribbean Sea,” was recently published in Nature Scientific Reports and is available at: https://doi.org/10.1038/s41598-025-08709-5.

Tropical corals are struggling to build solid reef structures. Even those species once thought to be especially resilient are now showing signs of decline. In a new study, researchers reconstructed more than one hundred years of growth in the Caribbean coral Siderastrea siderea using samples collected off the coast of Martinique. The findings reveal a steady drop in calcification rates throughout most of the twentieth century, with a sharp downturn beginning in the 1980s as marine heatwaves – driven by human-caused climate change – became more frequent.

One of the study’s most concerning findings is the sharp decline in coral skeletal density between 2010 and 2020 – a drop of 10.5 percent. This points to structural weakening caused by multiple interacting stressors. Signs of decline have been visible since the 1950s, when reef growth rates began to slow. At the time, scientists primarily linked the trend to local pressures such as coastal development and water pollution.

“Our study shows that while local protection measures remain important, they won’t be enough on their own,” says Gabriel Cardoso, coral researcher at Freie Universität Berlin’s Institute of Geological Sciences and first author of the study. “Without a significant reduction in global CO₂ emissions, even the most resilient coral species – and the reefs they build – will be at serious risk in the long term. The consequences could be severe. Coral reefs help protect against coastal erosion, provide habitats for countless marine organisms, and support livelihoods through fishing and tourism.”

Coral reefs are largely formed through the gradual growth of corals, which build their skeletons by depositing layers of calcium carbonate, a process known as “calcification.” These layers create annual growth bands – much like the rings in a tree trunk – that can be made visible using X-ray imaging and analyzed digitally. For this study, the research team examined coral growth in southern Martinique, using data collected from twelve drilled cores taken from four different reef sites. The samples span the period from 1912 to 2020 and provide a detailed record of how coral growth and calcification rates have changed over time. This research project was funded by the European Union’s Horizon 2020 research and innovation program through the project “Marine Coastal Ecosystems – Biodiversity and Services in a Changing World” (MaCoBioS, https://macobios.eu).