HiNews
Pink “rock reefs” in Scotland are already living in the future ocean, enduring low pH conditions similar to those projected for 2100—and doing it for most of the year. The finding suggests that these humble algae-built habitats may be tougher, and more important for marine biodiversity, than many climate forecasts assumed.
A reef that looks like stone, but isn’t
To casual eyes, coralline algae look like pinkish crusts cementing rocks together on the seafloor. In reality, this red seaweed slowly builds rigid, knobbly “reefs” by laying down calcium carbonate—similar to corals—creating shelter and nursery grounds for invertebrates, fish and other seaweeds. These reefs occur in cold and temperate seas worldwide and are considered highly sensitive to ocean acidification, because more acidic water can dissolve their chalky skeletons and weaken the habitat they provide.
Living with 2100-level acidity today
The new study monitored a coralline algae reef off western Scotland for a full year, tracking pH, temperature and dissolved oxygen through tides, seasons and day–night cycles. The team found that pH at this site naturally dips to values as low as those expected globally by 2100—even under a low-emissions scenario—for about 63% of the year, including most of autumn and all of winter.
These swings are not just occasional pulses. Annual pH at the reef varied by about 0.46 units, driven by biological activity, tidal mixing and seasonal temperature changes that together created a complex, constantly shifting chemical environment. When photosynthesis and respiration ramped up, changes in dissolved oxygen and pH rose and fell in tandem, while in winter, temperature and pH also moved together.[diva-portal]
A harsh training ground for future oceans
When researchers projected this natural variability into future climate scenarios, the lowest pH extremes at the site dipped beyond what current IPCC emission pathways typically represent. Yet the coralline algae reef persists under this regime, suggesting long-term exposure has already pushed these communities to acclimate or adapt to chronically low pH. Laboratory experiments and other field studies have hinted that coralline algae can sometimes maintain growth by adjusting calcification under reduced pH, especially when change is gradual rather than abrupt. The Scottish reef appears to be a real-world example of such “training,” where generations have grown up in a chemically challenging environment.
Cautious optimism for a changing ocean
The study does not mean ocean acidification is harmless, or that all coralline reefs will fare as well. Many habitats elsewhere experience much smaller pH swings today and could be hit harder as global chemistry shifts. But these pink Scottish reefs show that some biodiversity-rich systems already operate at the edge of future conditions—and still support complex communities—offering a rare, evidence-based dose of optimism for marine conservation.
For policymakers and marine managers, such naturally extreme sites may act as living laboratories, helping identify which habitats and species have the best odds of enduring the coming century’s chemical changes, and where protection could yield the greatest ecological payoff.
