Rates of primary productivity and growth in Ecklonia radiata measured at different depths, over an annual cycle, at West Island, South Australia

The pattern of growth (biomass accumulation) in Ecklonia radiata throughout the year and across a depth profile was investigated using the traditional “hole-punch” method, and the information presented in context with concurrently measured in situ net productivity rates. The rate of net daily productivity showed a lack of consistent seasonal variability, remaining constant throughout the year at two of the four depths measured (3 m and 12 m), and becoming higher during winter at another (5 m). Throughout the year, rates of net daily productivity differed significantly across the depth profile. Net daily productivity rates averaged 0.017 g C g−1 dwt day−1 and 0.005 g C g−1 dwt day−1 at a depth of 3 m (1,394 μmol O2 g−1 dwt day−1) and 10 m (382 μmol O2 g−1 dwt day−1) respectively. In contrast, the biomass accumulation rate of E. radiata was highly seasonal, with low rates of growth occurring in autumn (0.002 g dwt g−1 dwt day−1 at both 3 and 10 m) and summer (0.007 and 0.004 g dwt g−1 dwt day−1 at 3 and 10 m respectively) and higher rates in spring (0.016 and 0.007 g dwt g−1 dwt day−1 at 3 and 10 m respectively) and winter (0.015 and 0.008 g dwt g−1 dwt day−1 at 3 and 10 m respectively). The proportion of assimilated carbon used for biomass accumulation varied throughout the year, between 5% and 41% at 3 m and between 28% and 128% at 10 m. The rates of biomass accumulation at all depths represented only a small proportion of the amount of carbon assimilated annually.