Settlement and population dynamics of the alien invasive Branchiomma bairdi (Annelida: Sabellidae) in the Mediterranean Sea: two years of observations in the Gulf of Taranto (Italy)

Since the first discovery along the Italian coasts in 2004 of the polychaete Branchiomma bairdi, it has spread very quickly, reaching some localities in very high densities. In order to monitor its colonization, recruitment was investigated by means of PVC panels immersed in the Mar Grande of Taranto (Ionian Sea). Panels were monitored every three months from April 2013 to January 2015. The species showed the ability to settle on bare panels as well as on panels with a developed fouling community. Two years of monitoring identified two different cohorts, with recruits appearing in both years on panels submersed from July to October. Based on these observations B. bairdi is a short-lived species (no more than one year), reproducing at a temperature ranging from 20 to 29°C and reaching sexual maturity three months after recruitment. Oocytes were found in the coelom only in the warmest months and oogenesis was not synchronous either within each individual or within the population. Total annual secondary production was estimated at 43.42 g m−2 year−1. Annual mean biomass was 20.03 g m−2. The corresponding P/B ratio was 2.1678. This study may explain the invasiveness of B. bairdi; indeed, a rapid generation turnover coupled with a short lifespan, rapid growth and early maturity are common traits in most invasive species.