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Abstract

One of the options to mitigate atmospheric CO2 increase is CO2 Capture
and Storage in sub-seabed geological formations. Since predicting
long-term storage security is difficult, different CO2 leakage scenarios
and impacts on marine ecosystems require evaluation. Submarine CO2 vents
may serve as natural analogues and allow studying the effects of CO2
leakage in a holistic approach. At the study site east of Basiluzzo
Islet off Panarea Island (Italy), gas emissions (90-99% CO2) occur at
moderate flows (80-120 Lm(-2) h(-1)). We investigated the effects of
acidified porewater conditions (pH(T) range: 5.5-7.7) on the diversity
of benthic bacteria and invertebrates by sampling natural sediments in
three subsequent years and by performing a transplantation experiment
with a duration of one year, respectively. Both multiple years and one
year of exposure to acidified porewater conditions reduced the number of
benthic bacterial operational taxonomic units and invertebrate species
diversity by 30-80%. Reduced biodiversity at the vent sites increased
the temporal variability in bacterial and nematode community biomass,
abundance and composition. While the release from CO2 exposure resulted
in a full recovery of nematode species diversity within one year,
bacterial diversity remained affected. Overall our findings showed that
seawater acidification, induced by seafloor CO2 emissions, was
responsible for loss of diversity across different size-classes of
benthic organisms, which reduced community stability with potential
relapses on ecosystem resilience.