Seasonal variations of epilithic diatoms on different hard substrates in the northern Adriatic Sea

The colonization of epilithic diatoms on artificial hard substrates (marble, quartzite and slate) was investigated on a seasonal basis in a subtidal site of the northern Adriatic Sea to determine if substrate-dependent differences in colonization occurs and to define the seasonal variations of microepilithic communities in terms of abundance, biomass and community structure. Artificial substrates (smoothed small discs mounted on a Plexiglas sheet) were placed at a depth of 8 m in April 2003, July 2003, January 2004 and February 2004. The discs were collected after 6-7 weeks for counting and taxonomic identification of the diatoms. The community structure of epilithic diatoms showed a dominance of motile species over the entire study period, followed by erect, adnate and tube-dwelling diatoms. Diatom density showed a marked seasonal variability, ranging from 365±407 (winter 2004) to 557156±82602 cells cm-2 (spring 2004). Biomass ranged from 0.02±0.01 to 17.53±3.20 μg C cm-2. Abundance and biomass values did not present any significant differences for the three substrates examined.