Three years seasonal dynamics of the northern Adriatic soft-bottom Polychaete assemblages

Although the taxonomic composition of the northern Adriatic soft-bottom Polychaete assemblages is well explored, very little is known about their annual dynamics. Polychaetes were investigated seasonally from March 2003 to December 2006 on three offshore stations in the communities of coastal detritic and muddy coastal detritic bottoms. Sediment samples were collected with 0,1 m2 Van Veen grab and sieved through 2 mm and 1 mm mesh size consequently. Preliminary results of the analyses of 2 mm samples are given. 7295 Polychaetes were examined and 141 species belonging to 36 families were identified. This number represents 20% of the known Adriatic Polychaete fauna to date. Comparison with previous investigations indicates relatively rich Polychaete fauna in the research area. Seasonal fluctuation of abundance was different on three stations and didn’t show periodical pattern but was influenced by the population dynamics of characteristic and dominant species. Increase and decrease of abundance was not closely followed by the growth and reduction of species richness. The most abundant species, mutual for three stations, Notomastus latericeus, Owenia fusiformis and Myriochele oculata are characteristic species of detritic and muddy detritic bottoms. Analysis of population dynamics of species Owenia fusiformis and Notomastus latericeus revealed different pattern than in previous research. Reproductive features of these cosmopolitan species seem to be peculiar to certain population rather then the species itself and depend on different environmental conditions. Low seasonal alterations of structure and dynamics of Polychaete assemblages are consistent with the stable environmental conditions during research period.