Reproduction, population dynamics and production of Nereis falsa (Nereididae: Polychaeta) on the rocky coast of El Kala National Park, Algeria

The polychaete Nereis falsa Quatrefages, 1866 is present in the area of El Kala National Park on the East coast of Algeria. Field investigations were carried out from January to December 2007 to characterize the populations' reproductive cycle, secondary production and dynamics. Reproduction followed the atokous type, and spawning occured from mid-June to the end of August/early September when sea temperature was highest (20-23A degrees C). The diameter of mature oocytes was approximately 180 mu m. Mean lifespan was estimated to about one year. In 2007, the mean density was 11.27 ind. m(-2) with a minimum of 7.83 ind. m(-2) in April and a maximum of 14.5 ind. m(-2) in February. The mean annual biomass was 1.36 g m(-2) (fresh weight) with a minimum of 0.86 g m(-2) in December and a maximum of 2.00 g m(-2) in June. The population consisted of two cohorts distinguishable from size frequency distributions. One cohort corresponded to the recruitment of 2006 and the other appeared during the study period in September 2007. The annual production of N. falsa was 1.45 g m(-2) year(-1), and the production/biomass ratio was 1.07 year(-1).