lithophaga colonizing artificial and natural structures

Shell width and body live weight related to shell length of the endolithic bivalve Lithophaga lithophaga (date mussel) colonizing a specific habitat (vaults under boulders) formed by artificial and natural structures were examined. Artificial structures consisted of limestone boulders of a breakwater (Marina Rovinj, northern Adriatic Sea, Croatia) constructed 19 years before sampling of the date mussel. Date mussels ’ density (around 80 individuals per 0.1 m2) did not differ between the two types of structure. However, the length frequency distribution in artificial structures (25th percentile = 3.20, median = 4.30 and 75th percentile = 5.10 cm) differed from that in natural structures (25th percentile = 3.66, median = 5.15 and 75th percentile = 6.20 cm) leading to a sub-stantial difference in total biomass (0.3 and 0.8 kg per 0.1 m2 for artificial and natural structures, respectively). Parameter estimates of regression functions for width against length (linear func-tion) and for live weight against length (allometric function) also significantly differed, indicating variations in date mussels ’ morphometry between the two types of structure. Analyses of variance did not detect differences in width or weight for date mussels in the length range from 3 to 3.5 cm. However, width (average ± s.d., n = 18) of individuals in the range from 5.5 to 6 cm was significantly lower in artificial structures (1.46 ± 0.13 cm) than in natural structures (1.66 ± 0.1