Acclimatization of the invasive sabellid Branchioma bairdi (Anellida) at ocean acidification. Preliminary results of a transplant experiment at a CO2 vent system.

Branchiomma bairdi is a sabellid polychaete native of the Caribbean Sea and recently introduced in the Mediterranean Sea where the species’s range has rapidly expanded as a consequence of its ability to colonize different environments and substrates. The species has also been reported around Ischia (Naples, Italy), a volcanic Island characterized by numerous submerged CO2 vent systems. In this regard the species occurs at the Castello vent system where intense CO2 emissions along the rocky reef lower the seawater pH up to mean values >7.4. In order to investigate the physiological response of B. bairdi to seawater acidification, worms were collected from the Mar Grande of Taranto, a non-acidified area in the south of Italy, and transported to Ischia in order to perform a transplant experiment into naturally acidified conditions. Three acidified plots were selected around the Castello vent’s area (A4, A5 on the south side; A6 on the north side), and three plots on a control area located at S. Pietro point (mean pH 8.12), approx 4 km from the Castello (C1, C2, C3). Thirty individuals per plot (90 per treatment) were exposed inside plastic cages, to both acidified and control conditions for 30 days. Cages were monitored and pH and temperature were measured in each plot approx. every four days until the end of the experiment. In addition, some individuals sampled both in Taranto and the Castello acidified area were frozen immediately after collection and used as a background condition test. The physiological response of B. bairdi to the acidified treatment was inferred measuring the activity of carbonic anhydrase (CA) a zinc metalloenzyme involved in a wide variety of physiological processes in animals. CA enzymatic activity was measured by electrometric method on the whole body homogenate of the species. CA activity data from the in vivo exposure experiment were analyzed by two-way ANOVA. No significant differences (p>0.05) in CA activity between acidified and control treatment were observed both in the transplanted and background worms, suggesting that this invasive species shows high physiological plasticity and it is well acclimatized to the acidified conditions of the Castello vent system.