Population structure, growth and production of Thoracophelia furcifera (Polychaeta: Opheliidae) on a sandy beach in Southern Brazil

This study investigates aspects of the life his- tory of the polychaete Thoracophelia furcifera on a sandy beach in southern Brazil. Two fixed transects perpendicular to the shoreline in the intertidal zone were sampled fort- nightly from May 2008 to April 2009 at low tide. Five T. furcifera samples were collected along each transect and sediment temperature and the salinity of interstitial water were recorded. The material was washed over 0.5- and 0.088-mm sieves, and the width of setiger 8 of each specimen was measured. A total of 5,870 organisms were examined and the estimated parameters of the von Berta- lanffy growth curve were L? 3.60 mm (Wd8S), K 0.63 year -1 , C 0.3 and WP 0.97 (Rn 0.132). Life span was 2.6 years, instantaneous mortality rate Z was 3.8 year -1 and the growth index u 0 0.91. Mean density ranged from 644.44 ± 191.77 to 2,783.33 ± 453.64 ind m -2 and mean biomass ranged from 2.52 ± 0.55 to 9.52 ± 1.83 g m -2 . Recruitment occurred from April to July and ovigerous females were found from June to November. Annual sec- ondary production was 6.582 g m -2 year -1 , mean biomass was 5.638 g m -2 and turnover rate was 1.167. The high values for density, secondary production and biomass suggest that T. furcifera constitute an important food source. These features of T. furcifera' life strategy dem- onstrate the significant role this species plays in ecosystem dynamics.