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.