Production of Excirolana armata (Dana, 1853) (Isopoda, Cirolanidae) on an exposed sandy beach in southeastern Brazil

The somatic and gonad productions of the cirolanid isopod Excirolana armata were analyzed by taking monthly samples from December 2003 to November 2005 on Una beach, S?o Paulo state (24°S), southeastern Brazil. Sampling was performed along three fixed transects established from the base of the foredunes to the waterline. Weight-specific growth rate was used to estimate the E. armata somatic production for 2004 and 2005, separately. The gonad production was estimated based on the monthly reproductive potential (mean number of eggs/embryos per female × monthly abundance of ovigerous females with near-release broods) for 2004. The annual somatic production of E. armata population varied from 15.57 to 17.25?g AFDW m^?1?year^?1 and the somatic production/biomass ratio (P _s/B) from 3.55 to 3.14?year^?1 for 2004 and 2005, respectively. The P _s/B ratios were higher for males (4.02 and 3.19?year^?1 for 2004 and 2005) than for females (3.10?year^?1 for both years). The annual gonad production (P _g?=?1.07?g AFDW m^?1?year^?1) contributed about 15 and 6% to the total production (P _s?+?P _g) of females and the population, respectively. The proportion of gonad to somatic production of females (P _g/P _s) increased with individual size (ca 90% in the 7.5?mm size class), and the annual weight-specific gonad production (P _g/B ratio) was estimated to 0.24?year^?1. The high P _s/B ratios estimated for E. armata derive from the fast growth of individuals and show the importance of this population to the energy flow on Una beach ecosystem. However, the low percentage of juveniles verified in this population and in other studies of populations of the genus Excirolana is discussed as an important source of underestimation of P _s/B ratio.