New insights on Antarctic gorgonians' age, growth and their potential as paleorecords

•Longevity in Antarctic gorgonians was confirmed, with lifespans of hundreds of years.•RGR of Thouarella species were the lowest ever reported for any gorgonian species.•SEM microanalyses identified carbonate-rich and organic-rich layers in the skeletons.

Antarctic benthic communities have long been regarded as relicts of the past, since they have developed in a very stable environment and are formed by slow-growing and extraordinary long-lived organisms. However, little is known about the life history traits of gorgonian species, which are considered key components of the Antarctic benthos. In this study, age, Radial Growth Rates (RGR) and skeletal composition of Thouarella variabilis, Fannyella abies and Fannyella rossii colonies (Octocorallia, Primnoidae) that inhabit Antarctic shelf waters were examined. The radioisotopes 14C and 210Pb used for dating revealed that these colonies are long-lived, with ages spanning from 50 to 1100 years, thus confirming the archaic character of the Antarctic ecosystem. Some RGR obtained are among the lowest rates ever reported for primnoid species and gorgonians as a whole, with Thouarella species showing rates of 5.08 µm yr−1. Growth ring deposition seemed to occur every 2–3 years on average, although this result cannot be confirmed. Irregularities in the growth rings could be observed under the Scanning Electron Microscope (SEM) as fluctuations in the skeletal composition, which may be indicative of changes in the environmental conditions, most possibly primary production.