<jats:p>We analysed growth of the arborescent Antarctic cheilostome bryozoan <jats:italic>Cellaria incula</jats:italic> by stable carbon and oxygen isotope analysis. The growth of one complete branch of <jats:italic>C. incula</jats:italic> takes one year, i.e. owing to the bifurcate colony structure two new branches grow from each branch of the previous generation. The maximum age of a <jats:italic>C. incula</jats:italic> colony is likely to be more than 14 years. Annual production-to-biomass ratio is 0.67, the highest value hitherto measured for any benthic invertebrate south of 62°S. Comparatively fast growth and high productivity identify <jats:italic>C. incula</jats:italic> as a pioneer species which is able to quickly occupy spatial niches produced by iceberg scouring on the Antarctic shelf.</jats:p>