Population dynamics and secondary production of Owenia fusiformis Delle Chiaje (Polychaeta Oweniidae) along the coasts of Emilia-Romagna (Northern Adriatic, Mediterranean Sea)

The population structure and dynamics of O. fusiformis have been studied for one annual cycle along the coasts of Emilia-Romagna (Italy). Five seasonal samplings were carried out along two transects differently influenced by the Po river outflow, at the depth of 3, 8 and 12 m, using a 0.06 m(2) Van Veen grab. Secondary production has been evaluated according to the increment weight method. Densities and biomass values were higher at 8 m depth in both the considered localities, probably due to lower mud content of the sediment. The pattern of size-frequency histograms suggests an estimated life-span of at least two years. The growth rate of the youngest individuals was higher at 3 m depth, due to the higher hydrodynamic levels of the shallower waters. Total annual production ranged from a minimum of 0.12 g m(-2) y(-1) at the depth of 12 m off Cesenatico, to a maximum of 14.78 g m(-2) y(-1) at the depth of 3 m off Porto Garibaldi.