EVects of ocean acidiWcation on invertebrate settlement at volcanic CO2 vents

We present the Wrst study of the eVects of ocean acidiWcation on settlement of benthic invertebrates and microfauna. ArtiWcial collectors were placed for 1 month along pH gradients at CO2 vents oV Ischia (Tyrrhenian Sea, Italy). Seventy-nine taxa were identiWed from six main taxonomic groups (foraminiferans, nematodes, polychaetes, molluscs, crustaceans and chaetognaths). Calcareous foraminiferans, serpulid polychaetes, gastropods and bivalves showed highly signiWcant reductions in recruitment to the collectors as pCO2 rose from normal (336–341 ppm, pH 8.09–8.15) to high levels (886–5,148 ppm) causing acidiWed conditions near the vents (pH 7.08–7.79). Only the syllid polychaete Syllis prolifera had higher abundances at the most acidiWed station, although a wide range of polychaetes and small crustaceans was able to settle and survive under these conditions. A few taxa (Amphiglena mediterranea, Leptochelia dubia, Caprella acanthifera) were particularly abundant at stations acidiWed by intermediate amounts of CO2 (pH 7.41–7.99). These results show that increased levels of CO2 can profoundly aVect the settlement of a wide range of benthic organisms.