Rafael León

Body Size, Growth and Life Span: Implications for the Polewards Range Shift of Octopus tetricus in South-Eastern Australia

Understanding the response of any species to climate change can be challenging. However, in short-lived species the faster turnover of generations may facilitate the examination of responses associated with longer-term environmental change. Octopus tetricus, a commercially important species, has undergone a recent polewards range shift in the coastal waters of south-eastern Australia, thought to be associated with the southerly extension of the warm East Australian Current. At the cooler temperatures of a polewards distribution limit, growth of a species could be slower, potentially leading to a bigger body size and resulting in a slower population turnover, affecting population viability at the extreme of the distribution. Growth rates, body size, and life span of O. tetricus were examined at the leading edge of a polewards range shift in Tasmanian waters (40°S and 147°E) throughout 2011. Octopus tetricus had a relatively small body size and short lifespan of approximately 11 months that, despite cooler temperatures, would allow a high rate of population turnover and may facilitate the population increase necessary for successful establishment in the new extended area of the range. Temperature, food availability and gender appear to influence growth rate. Individuals that hatched during cooler and more productive conditions, but grew during warming conditions, exhibited faster growth rates and reached smaller body sizes than individuals that hatched into warmer waters but grew during cooling conditions. This study suggests that fast growth, small body size and associated rapid population turnover may facilitate the range shift of O. tetricus into Tasmanian waters.

Reproductive capacity of a marine species (Octopus tetricus) within a recent range extension area

To persist in the face of environmental change, species must adjust to the new conditions or change their geographical distribution, e.g. by range extension. Success for individuals within a zone of range extension requires the new environment to support their capacity to produce viable gametes and survival of the offspring. Reproductive characteristics of the polewards range-shifting Octopus tetricus were examined within the new range off north-eastern Tasmania, Australia, to assess whether it is likely to successfully establish in this extended area of its range. Approximately 44% of captured males and 14% of captured females were mature. Mature females with developing eggs were found throughout the year. Greater numbers of mature females were observed during the austral summer and spring, whereas mature males were observed all year round. Fecundity was high and developing embryos appeared to be viable. Our results suggest that O. tetricus is successfully reproducing beyond its historical range, the reproductive cycle is timed to favourable environmental conditions, and the population has the potential to be self-sustainable. The reproductive biology of O. tetricus may thus facilitate the establishment and prevalence of the population into new environments beyond the known historical distribution.