Ocean acidification has been shown to have highly variable effects, with many negative and some positive
responses from individual species, while community level effects are largely unknown. Although an overall
loss of biodiversity is expected, predicting the effects of ocean acidification on whole assemblages can be
problematic as both direct and indirect effects of acidification must be taken into consideration. This study
demonstrates how invertebrate assemblages associated with the highly productive seagrass, Posidonia oceanica,
respond to natural acidification that occurs at CO2 vents off the coast of Italy. We examined seasonal differences
in invertebrate community structure between two distinct pH zones: control (pH 8.1) and acidified (pH 7.8) and
showthat many groups of invertebrate taxa were robust to acidification effects. Differences in community structure
appeared to be driven by the indirect effects of acidification, such as changes to canopy structure and food
availability, rather than physiological intolerance to low pH. The number of invertebrates collected in acidified
stationswas almost double that of control stations during the study and many heavily calcified species appeared
to thrive. These results highlight how positive indirect effects may buffer the ecological impacts of acidification,
and provide evidence that this highly productive, nearshore habitatmay provide refuge to its associated communities
from future ocean acidification