Bivalve farmers are already noticing the impact, especially off the northwest coast of North America
Damage to coral reefs, loss of habitats and a threat to survival for shell-building marine creatures are among the impacts already being felt from ocean acidification.
Until now, it had not been deemed to have crossed its “planetary boundary” (defined as a 20 percent aragonite saturation state change compared to pre-industrial times). However a major new study, led by Plymouth Marine Laboratory (PML), the US National Oceanic and Atmospheric Administration (NOAA) and Oregon State University has found that this boundary – in effect a safety limit – was actually reached around five years ago.
The study, titled Ocean Acidification: Another Planetary Boundary Crossed in the journal Global Change Biology, used the latest physical and chemical measurements in the upper ocean, combined with advanced computer models and studies of marine life, and concluded that:
- By 2020, the average ocean condition worldwide was already very close to, and in some regions beyond, the “danger zone” for ocean acidification.
- Exploring deeper into the ocean (down to about 200m below the surface), it was discovered that around 60 percent of these deeper waters had crossed the boundary, compared to 40 percent of the water at the surface. This increase in ocean acidification has major implications for the survival of many sea creatures, especially those that build shells or skeletons from calcium carbonate.
- The damage is already showing: selected tropical and subtropical coral reefs have lost 43 percent of their suitable habitats, sea butterflies (pteropods, a key foodweb species) in polar regions have lost up to 61 percent of their habitat, and coastal shellfish species have lost 13 percent of their global coastline habitats in which they can sustain their essential biological processes.
Based on these findings, the scientists have recommended the revision of the previous safety limit – establishing that even a 10 percent change from pre-industrial levels would be harmful to ocean ecosystems. Unfortunately, the entire ocean surface had already passed this stricter limit by around the year 2000.
There are also regional considerations, as report lead author and chair of the North-East Atlantic Ocean Acidification (NEA-OA) Hub - PML’s Professor Helen Findlay - explained in a press release: “Looking across different areas of the world, the polar regions show the biggest changes in ocean acidification at the surface. Meanwhile, in deeper waters, the largest changes are happening in areas just outside the poles and in the upwelling regions along the west coast of North America and near the equator.”
“Most ocean life doesn't just live at the surface – the waters below are home to many more different types of plants and animals. Since these deeper waters are changing so much, the impacts of ocean acidification could be far worse than we thought. This has huge implications for important underwater ecosystems like tropical and even deep-sea coral reefs that provide essential habitats and nursing refuge for many species, in addition to the impacts being felt on bottom-dwelling creatures like crabs, sea stars and other shellfish such as mussels and oysters.”
Ocean acidification also reduces the availability of calcium carbonate, a crucial building block that many marine organisms need to form shells and skeletons. As pH levels drop, calcifying species such as corals, oysters, mussels and tiny sea butterflies struggle to maintain their protective structures, leading to weaker shells, slower growth, reduced reproduction and decreased survival rates.
“Ocean acidification isn't just an environmental crisis – it's a ticking time bomb for marine ecosystems and coastal economies. As our seas increase in acidity, we're witnessing the loss of critical habitats that countless marine species depend on and this, in turn, has major societal and economic implications,” says PML’s director of science, Professor Steve Widdicombe, who is also co-chair of GOA-ON, the Global Ocean Acidification Observing Network.
“From the coral reefs that support tourism to the shellfish industries that sustain coastal communities, we're gambling with both biodiversity and billions in economic value every day that action is delayed.”
Conservation opportunities?
The study suggests that conservation measures should focus on the regions and species most vulnerable to acidification. The authors also stress the importance of protection or suitable management measures for those areas least compromised to ensure their longevity.
The newly identified impacts in subsurface waters point to an urgent need to protect mid-water habitats and the creatures that depend on them. Furthermore, the research team emphasises the importance of improved management approaches to address ocean acidification, alongside other pressures facing the ocean, to support stronger ecosystem resilience.
