A new study of coral reefs in Papua New Guinea, conducted by a research team led by Professor Ivan Nagelkerken from the University of Adelaide, reveals that ocean acidification simplifies coral structure, making essential habitats less appealing to certain fish species. This study was published in the Journal of Animal Ecology.
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While much media attention has been directed toward heat stress-induced coral bleaching, this finding adds nuance to concerns about how global warming impacts coral reefs.
Ocean acidification is the result of rising carbon dioxide levels in ocean water, which lowers pH. As a result, there is less calcium carbonate in the water, which corals need to maintain and rebuild their skeletons.
While ocean acidification may not always result in a decrease in the total amount of coral cover on a reef, Professor Nagelkerken and his colleagues' research demonstrates that the structures become less branching and, as a result, less desirable to certain fish species as a habitat.
In Upa-Upasina, Papua New Guinea, scientists noticed two reefs: One 500 m away from the volcanic seep that was producing a continuous stream of carbon dioxide that was causing natural acidification, and another reef not affected by the volcanic gasses.
Aquarium experiments are rather simplistic and cannot adequately mimic the complex species interactions that commonly occur in nature.
Ivan Nagelkerken, Professor, School of Biological Sciences, University of Adelaide
Nagelkerken said, “These reefs presented an incredible opportunity to directly compare current and future-analogous conditions side-by-side, with a full suite of ecological interactions in place.”
Out of the five species of damselfish that Professor Nagelkerken's team studied, two showed a predilection for intricate, branching structures; the other two showed no aversion to interacting with simpler coral structures but continued to seek out complicated habitats even as they became more scarce. The species with the strongest association with rubble was a fifth rubble specialist.
Ocean acidification has the potential to reshuffle ecological communities globally, lead to the loss of key habitats and biodiversity, reduce fisheries’ productivity, and have negative physiological impacts on many marine animals and plants.
Ivan Nagelkerken, Professor, School of Biological Sciences, University of Adelaide
Nagelkerken said, “It might also lead to a reduction in populations of various fish species, which could create novel species community structures that might have lower biodiversity and not be as resilient as present-day communities. It could also clearly distinguish the winning species from the loser species. And if this ocean acidification affects fisheries species, some species that recreational and commercial fishers target might become less abundant.”
As more and more carbon emissions from human activity enter the Earth's atmosphere and are absorbed by the ocean, acidification circumstances similar to those seen at the reef next to the volcanic seep which was documented are predicted to occur throughout the ocean.
“If we continue to emit carbon dioxide unabated, at some point in the future we could see such levels of ocean acidification in Australia,” said Professor Nagelkerken who worked alongside colleagues from James Cook University as part of an international team that included researchers from New Caledonia, Hong Kong and Japan.
The effects observed in our study would be similar in Australian ecosystems because many of the coral and fish species that we studied in Papua New Guinea also occur on the Great Barrier Reef.
Ivan Nagelkerken, Professor, School of Biological Sciences, University of Adelaide
Professor Nagelkerken explained, “But temperate reefs might also be affected, with ocean acidification having negative effects on cold-water reef builders such as oysters, mussels, and calcareous algae, among others.”
Professor Nagelkerken says there is an easy method to prevent this impending future. “We should increase our efforts to reduce CO2 emissions globally,” he said.
Journal Reference:
Priest, J., et al. (2024) Out of shape: Ocean acidification simplifies coral reef architecture and reshuffles fish assemblages. Journal of Animal Ecology. doi.org/10.1111/1365-2656.14127.