Abstract
AbstractStructure and diversity of sessile zoobenthic assemblages seem to be driven not only by chemical-physical constraints and biological interactions but also by substrate lithology and its surface features. Nevertheless, broadly distributed crustose epilithic corallines could mask the role of substrate on animal settling. To evaluate the direct influence of different rocky substrates, occurrence and coverage of several sessile species, growing on the dark (i.e. coralline-free) face of sublittoral limestone and granite boulders were compared in the Tavolara MPA (Mediterranean Sea). The analysis of photographic samples demonstrated significant differences in terms of species composition and coverage, according to lithology. Moreover, limestone boulders were widely bare, while the cover per cent was almost total on granite. The leading cause of observed patterns could be the different level of dissolution of the two types of rocks, due to their different mineral composition and textural characteristics. Limestone has previously been shown to have higher dissolution compared with granite, and consequently, a more unstable surface. Our results suggest that, in dark habitats, the absence of the crustose coralline layer allows more rock dissolution and consequent lower stability of the limestone compared with granite, which, in turn, reduces the zoobenthos colonization.
Highlights
The lithological characteristics of the substrate may influence the richness and dynamics of hard-bottom benthic assemblages (Cerrano et al, 1999; Bavestrello et al, 2000, 2018; Cattaneo-Vietti et al, 2002; Faimali et al, 2004; Johansen, 2018; Canessa et al, 2019, 2020)
Under comparable edaphic conditions, several communities were found to be structurally different on substrates of different lithology, in terms of presence and abundance of some sessile species (Coombes, 2011)
This paper aims to verify the open hypothesis that the settlement of sessile zoobenthic organisms and the consequent development of the assemblage in terms of richness and occurrence could be directly driven by the substrate lithology, without interference due to encrusting calcareous algae
Summary
The lithological characteristics of the substrate may influence the richness and dynamics of hard-bottom benthic assemblages (Cerrano et al, 1999; Bavestrello et al, 2000, 2018; Cattaneo-Vietti et al, 2002; Faimali et al, 2004; Johansen, 2018; Canessa et al, 2019, 2020). Under comparable edaphic conditions, several communities were found to be structurally different on substrates of different lithology, in terms of presence and abundance of some sessile species (Coombes, 2011). During tests performed using experimental blocks of different rocks along the coast of Cornwall, barnacle settling was higher on granites and concrete than on limestones, suggesting that the roughness of the substrate could positively influence settling (Coombes, 2011). The influence of different rock types was evident for the supralittoral barnacle Chthamalus spp. which, in the Ligurian Sea, appeared more abundant on limestones than on marly substrates (Canessa et al, 2019). Comparing barnacle populations living on different ophiolitic rocks, differences in density arose: they were abundant on serpentinite rocks and virtually absent on metagabbros (Bavestrello et al, 2018)
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