Benthic community on a concrete and coal-ash blocks submerged in an artificial reef in the Central Adriatic sea

In July 1993 concrete and coal ash cubic blocks (1x1x1 m) were submerged in the Senigallia artificial reef (Central Adriatic Sea), 1.2 miles offshore, on a sandy muddy bottom (11 m deep). The differences in the benthic community settled on the vertical and horizontal surfaces of the two substrates were investigated for one year (fall 1993 - summer 1994) through seasonal "grattages" of standard areas carried out by divers. Dominance index (D), total species richness (St), mean species richness (Sm) and mean Shannon Weaver diversity index (H') were separately computed for each season and for each substrate. Statistical comparison among the seasons and between vertical and horizontal surfaces of the two substrates was accomplished using the analysis of variance. The benthic community on concrete and coal ash blocks was dominated by polychaetes, crustaceans and molluscs. The highest values of total and mean species richness were obtained for the concrete. A gradual increase in Sm was observed on both substrates, with the maximum values in summer '94. The horizontal surfaces of coal ash blocks showed the lowest values for Sm and H', mainly due to a selective settlement of the burrowing bivalve Pholas dactylus. High significant differences among the seasons were obtained for the horizontal surfaces of both substrates, with the lowest values of Sm and H' in autumn '93. The vertical surfaces did not show any significant difference.