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

The population structure and dynamic 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 m2 Van Veen grab. Secondary production has been evaluated in accord to the increment weight method (Crisp 1984). 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.