Growth of the Antarctic octocoral Primnoella scotiae and predation by the anemone Dactylanthus antarcticus

Growth rates in Antarctic marine ectotherms have been demonstrated to be slowed by two to five times compared to shallow-water temperate species, with no previous reports for octocorals. Here growth rates were estimated in the single axis, non-branching Antarctic octocoral Primnoella scotiae using repeated in situ length measures covering both summer and winter periods, for tagged colonies from three sites at Signy Island over a two year period. Mean rates of length increase at the different sites ranged from 0.96 mm yr−1 to 55.3 mm yr−1. The fastest individual colony growth rate at any site ranged from 2.55 mm yr−1 to 175.6 mm yr−1. The mean of the fastest growth rates across all sites was 33.0 mm yr−1±14.7 (s.e.). Growth was significantly different between sites, and also between seasons and years. The mean overall increase in diameter of the average sized colony in the study (222.5 mm in axis length) was 0.053 mm yr−1. This is the slowest reported growth rate of any octocoral to date, and is five times slower than growth in most cold water octocorals. During the study it was noted that colonies were being attacked and consumed by the anemone Dactylanthus antarcticus. At one of the sites studied, between 5% and 8% of colonies surveyed were attacked each month. Anemone dispersal was via whole body inflation and drifting to new prey colonies that were attached to using tentacle-like column protuberances.