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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.

An exceptional assemblage of the sea fan Leptogorgia sarmentosa (Anthozoa: Gorgoniidae) was observed inside the Genoa harbour, which represents one of the major Mediterranean ports. The studied assemblage is confined in a shaded portion of a floating dock thriving in extremely shallow water, with specimens even touching the sea surface. It represents the shallowest population of this species and of this genus known worldwide. A total of 188 specimens were observed and measured: the maximum density of 45 specimens m(-2) was reached in the most shaded part of the dock, where the maximum height of colonies (30 cm) was also recorded. Light measurements showed that the illuminance along the dock was comparable to that observed outside the harbour at 20 m depth, where the nearest colonies of L. sarmentosa were recorded for this region. This suggests that high levels of incident light might be putatively interpreted as the limiting factor in the upper bathymetrical distribution of the species. Despite the extremely shallow distribution, however, the population cannot be defined as intertidal as the floating dock avoids exposing the gorgonians to air. The chance to grow far from the silted bottom, but still in a turbid, sciaphilous and nutrient-enriched environment, probably enhanced the settling and growth of the colonies and allowed the formation of a dense and healthy population.

In the last few decades, macrobenthic community structures and their species abundances have shown significant changes in the Mediterranean Sea, whose causes were attributed to anthropogenic activities and to global warming effects. The Mediterranean sponges have shown a peculiar sensitivity to these changes: the populations of some species showed significant decreases, while others, more thermophilous, increased. Therefore, sponges may be a good proxy for evaluating the effects of environmental changes. Thanks to the observations conducted by Sarà about 55 years ago, a comparative analysis of the sponge populations present within two semi-submerged caves in the Ligurian Sea was possible. The two sponge assemblages re-studied in 2016 showed an increase in terms of specific richness and a significant change in their structural aspects, since the three-dimensional growth forms were mostly replaced by two-dimensional ones, a process observed also in other littoral communities. Consequently, the sponge communities inside the semi-submerged caves may be considered poorly resilient: the massive sponges were hit by the positive thermal anomalies occurring in the Ligurian Sea in the last decade and were replaced by encrusting forms, within a possible phase of cave recolonisation.

During spring 2017, starting from 12 May, exceptional strandings of the purple snail Janthina pallida were recorded in the Ligurian Sea and along the western coast of Sardinia Island, under the effect of southern winds. The strandings continued for 3 days, until 15 May, when the winds shifted to the northern quadrant and the specimens were drifted back offshore. Such extensive strandings have never been previously reported in the scientific literature, either along the Mediterranean shores or elsewhere. Thanks to citizens’ help, it was possible to create a map of the strandings and obtain a gross estimate of the number of beached gastropods. The densities of the stranded animals reached an overall average of 801 ± 215 specimens m−2 (with peaks of over 2000 shells and rafts m−2 densely packed with hydrozoan Velella velella sails), corresponding to an average biomass of about 1.5 kg m−2. The size–frequency distribution of the shell heights showed a bi-modal trend, as is usual in the case of sequential hermaphroditism: almost all the specimens fitting the first mode (11 mm) showed a raft without eggs (males), while all the specimens belonging to the largest mode (23 mm) had rafts with settled egg cases (females). The general trend of the sea currents in the North-western Mediterranean Basin explains the spatial distribution of the strandings following 3 days of constant southern moderate breeze (up to 28 km h−1). The presence of such huge J. pallida banks in the Ligurian Sea is stochastic, probably linked to an Atlantic population entering through the Gibraltar Strait, as evidenced by the simultaneous presence of the buoy barnacle, Dosima fascicularis, a circumtropical species recorded here for the second time in the Mediterranean Sea.