Abstract
Settlement, recruitment and survival of sessile marine species are driven by many biotic and abiotic factors. Among them, substrate mineral composition is generally a neglected topic, despite it proved to be a relevant contributing variable in driving the structure of benthic communities. Thanks to their ecology, Chthamalus species are a good proxy to test the role of substrate in affecting settlement and final population density on exposed rocky shores. Differences in the number of individuals were analysed in eight localities along the Eastern Ligurian Riviera (north-western Mediterranean Sea), from Portovenere to Manara Cape. In this sector of the Ligurian littoral, the coast is constituted by different rocks characterised by variable concentrations of calcite, silicates and quartz. This situation constitutes an ideal setting to evaluate the influence of mineral composition of the rocks in structuring the epilithic macrobiota communities in energetic splash zones and under similar physical pressures. Rocks rich in calcites turned out to be more suitable for Chthamalus species than substrates containing high amounts of silicates, and of quartz in particular. Additionally, also the grain size of the main mineral component of the rocks, determining in turn the surface roughness seemed to influence barnacle densities, with a significant preference for finer-grained substrates.
Highlights
The characteristics of the Chthamalus belt in terms of population density were studied by photographic samplings during summer 2017 in eight selected localities, along 35 km of coastline from Portovenere, near the Gulf of La Spezia, to Manara Cape (Sestri Levante) (Table I; Figure 2)
The percentages of the major components (SiO2 and CaO) within the analysed rock substrates were quantified by Lithium Metaborate/Tetraborate Fusion followed by Inductively Coupled Plasma Mass Spectrometry (ICP/MS) at the ActLabs Laboratories (Ontario, Canada)
In the lower splash zone, densities were always smaller in all localities, excluding Bonassola: the maximum density (10,295 ± 1,942 individuals m−2) was observed at Portovenere Byron Cave and the minimum one at Manara Cape (1,017 ± 293 individuals m−2)
Summary
Changes and stability in spatial distribution, settlement, recruitment and density of marine sessile species are driven by a plethora of abiotic variables, which, in turn, interact with the biological ones (Dayton 1971; Keough & Downes 1982; Underwood et al 1983, 1984; Connell 1985; Menge & Sutherland 1987; Barry & Dayton 1991; Pawlik 1992; Raffaelli & Hawkins 1996; Smith & Witman 1999; Benedetti-Cecchi et al 2000; Sousa 2001; Menge & Branch 2001; Asnaghi et al 2015). Studies about their biology and ecology (Moore & Kitching 1939; Southward 1967, 1976, 1991; Levinton 1982; Underwood et al 1983, 1984; Caffey 1985; Moore & Seed 1985; Benedetti-Cecchi et al 2000; Bertness et al 2001; Underwood & Keough 2001), dispersal (Crisp & Southward 1958; Grosberg 1982), settlement (Larmon & Gabbott 1975; Crisp et al 1981; Hawkins & Hartnoll 1982, 1983; Gaines et al 1985; Gaines & Roughgarden 1985), recruitment and gregariousness (Lewis 1964; Underwood & Fairweather 1989; Sutherland 1990; Lively et al 1993; Southward et al 1995; O’Riordan et al 2004 and references therein; Jenkins et al 2000; Jenkins 2005), as well as competition and predation processes (Dungan 1985; Lively 1986a, 1986b; Lively & Raimondi 1987; Fairweather 1988; Raimondi 1988a, 1988b; Wahl 2009) have been widely explored topics in marine coastal ecology
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