Supplementary video related to this article can be found at
http://dx.doi.org/10.1016/j.marenvres.2014.12.004.
In scraped samples, sessile and vagile species were identified to
the lowest possible taxonomic level and their abundance was
estimated as number of individuals per sample.
In photographic samples organisms were identified by comparison
with a species reference collection (voucher specimens and
macro pictures) and assigned to morphological and ecological
groups (Ponti et al., 2011). Percent cover of sessile organisms was
estimated by superimposing a grid of 400 equal-sized cells (i.e.
0.25% each) and identifying all taxa visible within each cell
(Benedetti-Cecchi et al., 1996). Areas of photos that were too dark,
blurred or occupied by vagile organisms were excluded and percent
cover was adjusted according to the total readable area of each
image (Ponti et al., 2011). The endolithic bioeroder bivalve Rocellaria
dubia (Pennant, 1777) was identified and quantified by
counting its typical ‘8-shaped’ calcareous siphon holes. Percent