Have you ever swum in the crystal blue waters of an underwater volcanic vent, where tiny bubbles stream upwards, as if you are swimming in a glass of champagne?

Our research site is the island of Ischia, off the coast of Naples, Italy. Nature, culture and research on climate and oceans all converge on this unique Mediterranean island. One of our study sites is the underwater volcanic CO₂ vent located below the Castello Aragonese, a historic Roman fortress. Now, the fortress and the settlement are an Italian National historical monument. Below the fortress, there are volcanic CO₂ vents that locally acidify the seawater and it affects the surrounding ecosystems. The environmental characteristics of water carbonate chemistry and low pH values are used as a proxy to provide insights into acidification scenarios under IPCC Representative Concentration Pathways. These CO₂ vents are rare, only 15-20 sites like it are found in the world. They are like a “crystal ball” that shows the future of the world’s oceans in the face of ocean acidification (OA). OA reflects a decline in the surface ocean pH and a suite of changes in seawater chemistry due to the uptake of excess anthropogenic CO2 by the ocean. These naturally acidified systems are an ideal natural laboratory for examining whole-community responses to OA, which was our main research goal.

Previous studies using the volcanic CO₂ vents along the Castello, the first vent system studied in the world, generated key findings on the direct and indirect effects of OA on marine ecosystems. However, we wanted to add to new insights to improve our understanding of the ecological consequences of OA for marine biodiversity and ecosystem function. For that purpose, we were inspired by plant and fish-reef ecologists, with extensive experience in applying functional-trait approaches to quantified species loss in response to environmental change. 

Our research was the result of an international collaboration between seven ecologists from Italy, France, Spain, and the USA. The research merged complementary approaches, including field ecological surveys by SCUBA diving, taxonomic identification, ecological and statistical data analyses, and biogeochemistry, and the overall skills and expertise of our international team of marine and statistical ecologists.

Two extensive SCUBA field surveys were carried out in June 2015 and 2016 along the Castello vents. Our dataset was unique and novel, comprising the whole rocky reef community. We quantified the percent cover of 72 benthic species, which we characterized by coding the ecology of each species using 15 functional traits describing, among others: growth forms, longevity, size ranges, feeding characteristics and presence or absence of calcareous skeletons. We defined the traits and their categories; then we disentangled each species following them. Based on species cover and the functional entities (unique combination of functional traits), we linked species loss to shifts in functional diversity and redundancy following the acidification gradient. 

Overall, our results indicate that functional loss is more severe than anticipated based on taxonomic analyses. In addition, our analyses highlighted the life-history traits that are more vulnerable to ocean acidification such as such as tree-like and massive forms, long-lived and slow-growing life histories, heterotrophic feeding strategies and calcification. This integrative study attempted to advance our understanding into how future oceans will function in the face of OA. This is critical to assess the vulnerability of marine communities and the ecological services they provide us under ongoing and predicted global environmental change.   

View this amazing ecosystem of the Castello CO2 vents and newly discovered vents along the coast of Ischia

Nuria Teixidó, Maria Cristina Gambi, Valeriano Parravacini, Kristy Kroeker, Fiorenza Micheli Sebastien Villéger, Enric Ballesteros (2018) Functional biodiversity loss along natural CO2 gradients. Nature Communications. DOI: 10.1038/s41467-018-07592-1. https://www.nature.com/articles/s41467-018-07592-1