While many studies have focused on how ocean acidification may impact various individual species, an international team of researchers has just published a study on how an entire ecosystem can be affected by a more acidic ocean.
As one of the consequences of climate change, ocean acidification is expected to significantly increase if carbon emissions continue at current rates.
According to the study, which was published in Proceedings of the National Academy of Sciences (PNAS), ocean waters with higher levels of acidity will result in ecosystems with less diversity.
“The background, low-grade stress caused by ocean acidification can cause a whole shift in the ecosystem so that everything is dominated by the same plants, which tend to be turf algae,” said lead author Kristy Kroeker, a postdoctoral researcher at the Bodega Marine Laboratory at the University of California, Davis.
“In most ecosystems, there are lots of different colorful patches of plants and animals — of algae, of sponges, of anemones,” Kroeker explained. “With ocean acidification, you lose that patchiness. We call it a loss of functional diversity; everything looks the same.”
To reach their conclusion, the research team headed to Castello Aragonese, a 14th century castle off the western coast of Italy, at the northern end of the Gulf of Naples.
In the waters near the castle, natural volcanic vents release carbon dioxide gas, which creates a gradient of different levels of acidity for the surrounding area. This gradient allowed the research team to get a first-hand view of how increasingly acidic waters might look across time and how ecosystems may react to them.
First, the researchers selected three reef zones: low, high and extremely high acidity. Each area was used to represent world ocean conditions for the present day, 2100 and 2500, respectively. Next, the team removed animals and vegetation from the rocks in all three zones. Over the course of three years, Kroeker would dive to the different study regions every three months to photograph them and see how each recovered.
After analyzing the different recoveries among all three zones, the team found that the two regions with higher acidity recovered with a reduced number and variety of species.
In particular, they noted that turf algae would colonize and grow in the low acidity zone, only to be preyed upon by sea urchins and snails, which eventually allowed for increased diversity over time.
However, in the more acidic regions, the turf algae would grow to dominate the zones, as grazers avoided the area or did not prey on the algae while in these areas.
Known as calcareous grazers, sea urchins and snails play key roles in establishing and maintaining the balance within marine ecosystems. These species are also considered among the most susceptible to ocean acidification.
“Our research is showing that if the role of these grazers changes with ocean acidification, you might expect to see cascading effects of the whole ecosystem,” Kroeker said. “If the pattern holds for other calcareous grazers, this has implications for other ecosystems, as well.”
