Description CO2 vents
Ischia is a volcanic island where geology and biology are closely connected. Along its coast, there are special sites called ‘vents’ where bubbles of carbon dioxide (CO2) are released from the sea floor. This lowers the pH of the water, changing its physical and chemical properties and causing local marine acidification. The decrease in ocean pH and the alteration of the water’s physicochemical characteristics are phenomena already known to scientists globally, known as “ocean acidification”.
This phenomenon can have negative effects on marine organisms, especially those that build calcareous skeletons, such as corals and molluscs. In the Mediterranean and in other places around the world, there are other CO2 vent systems similar to those in Ischia. These sites are crucial because they represent natural laboratories that allows us to study and understand the effects of global environmental change in the near future, both on individual species and entire communities.
CO2 vent systems at the “Castello Aragonese”
One of the most well-known CO2 emission systems, and the first in the world to be studied to understand the effects of acidification on marine organisms, is the one located near the Aragonese Castle of Ischia. At this site, there are emissions of bubbles of carbon dioxide, creating a gradient of seawater acidification, from extremely low pH (pHT~6.5-7.2) to low pH (pHT~7.5-7.8) and ambient pH (pHT~ 8.0). The emission area extends on both the south and north sides of the Castello Aragonese.
The habitats characterizing these sites are primarily shallow rocky reefs covered with macroalgae and Posidonia oceanica meadows. P. oceanica is one of the most important marine plants in the Mediterranean.
Global Effects of CO2 and potential solutions
The ocean plays a fundamental role in the global climate, absorbing about 25% of the carbon dioxide we produce, making it an extremely important climate ‘regulator.’ Understanding the phenomenon of ocean acidification using natural marine laboratories, such as the vents of Ischia, is crucial for acquiring new insights into what will happen to the ocean and its ecosystems in the near future. This also allows us to consider possible nature-based solutions to mitigate it.
Preserving nature, including marine plants such as Posidonia oceanica, through conservation efforts and restoration actions, represents a potential nature-based solution to sustainably reduce the effects of ocean acidification and human impacts, helping to rebuild the health of our seas.
Suspended between two horizons: a view halfway between the emerged and submerged seascape of the Castello Aragonese where the presence of CO2 gas emissions can be seen. Photograph: Pasquale Vassallo
What’s boiling in the pot? A detail of one of the submerged areas of the Castello Aragonese characterized by intense CO2 emission activity, where a dense covering of macroalgae can be seen. Photograph: Pasquale Vassallo
A submerged garden: in the background, the meadow of the seagrass Posidonia oceanica and a school of salema fish, Sarpa salpa, the main herbivorous fish of the Mediterranean. Photograph: Pasquale Vassallo
A peaceful coexistence: a detail of a vegetated habitat characterized by patches of Posidonia oceanica and macroalgae of various species sharing space with the orange encrusting sponge Crambe crambe. Photograph: Pasquale Vassallo
I reel but I do not give up: A gastropod mollusc of the genus Patella with a bleached shell due to the corrosive action caused by low pH at CO2 vent sites. Photograph: Pasquale Vassallo.
Working beneath the surface: underwater scientific divers conducting a photographic transect to assess marine biodiversity along the acidification gradient at the Castello Aragonese. Photograph: Jeremy Carlot