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AbstractRecent studies suggest that the lithological properties of hard substrates play an important role in influencing the diversity and structure of marine assemblages involving macroalgae, sessile organisms and vagile animals like heterobranchs gastropods and fishes. The present study aims at exploring whether the influence of different substrates (limestone vs granite) could drive the occurrence of different vagile groups (crustacean decapods, echinoderms and fishes). The study was carried out at the “Tavolara-Punta Coda Cavallo” Marine Protected Area (NE Sardinia, Mediterranean Sea) where substrates of different lithology, namely granites and limestones, occur on a local spatial scale. The diversity and the abundance of 16 vagile species (four crustaceans, seven echinoderms and five fishes) were investigated by the analysis of photographs (2352 images) collected in 20 sites (10 limestones and 10 granites), between 30 and 50 m depth. Statistical analyses showed a clear-cut separation between the assemblages assessed on the two lithological substrate types, with assemblages on granites that were tightly grouped and those on limestones more dispersed. The total species richness did not significantly vary between limestones and granites. Galathea strigosaand Marthasterias glacialiswere exclusively recorded on granites, while Palinurus elephas, Scyllarides latus, Arbacia lixula, Ophidiaster ophidianusand Serranus scribawere exclusively found on limestones. The observed patterns could be partially explained by multiple factors related to lithology: i) the different availability of preferred food sources, potentially influenced by substrate type; ii) the site geomorphology, that could provide different dens and refuges (in terms of quantity and types of shelters) suitable for different species; iii) the colour of different substrates enhancing the mimicry of different species according to their livery and camouflage ability. Our and literature data suggest that the substrate type in rocky reefs could interact with other environmental factors (i.e., light intensity related to depth) in shaping the structure of rocky-reef assemblages.

AbstractThe occurrence, relative abundance and bathymetric distribution of the deep Mediterranean heterobranch fauna were evaluated as a result of an extensive visual census down to 1825 m depth, carried out along the western Italian coasts, covering a latitudinal range of about 600 nautical miles. Observations were conducted using Remotely Operated Vehicles (ROVs) in 551 sites, focusing on the deepest part of the continental shelf, the shelf edge and the upper bathyal zone. The analysis of over 508 hours of video footage and more than 27,000 high-resolution photographs allowed to explore about 594,000 m2of rocky outcrops and nearby soft seafloors in four main coastal areas (Ligurian Sea, north-central Tyrrhenian Sea, southern Tyrrhenian Sea, and Sicily Channel) and twelve offshore seamounts. Thirty-six species of heterobranchs, for a total of 559 records, were identified. Sixteen were only sporadically spotted (< 1% of the total observations), while three (Paraflabellina ischitana, Tritoniidae nd and Peltodoris atromaculata) contributed each for more than 10% of the records. An extension of the known Mediterranean bathymetric distribution was reported for 80% of the observed species, with many typically shallow-water taxa being also found in mesophotic environments (40–200 m). The observed marked decrease in diversity and abundance suggested that Mediterranean heterobranchs are mainly a coastal benthic group. From the geographical point of view, the heterobranch fauna present in the Ligurian Sea appeared significantly different from that observed in the Tyrrhenian Sea and the Sicily Channel, and this latitudinal pattern was discussed. Particular attention was given to single out the bathymetric distribution of the food sources of the most frequently observed species, supporting stenophagy as a limiting factor for their colonisation of the deep sea.

AbstractThe skeleton of most Porifera species consists of siliceous spicules that, after the sponge death, persist for a long time in the sediment. The reduced suspension occurring within the meadows of the seagrass Posidonia oceanicamakes these habitats a stable deposit for sponge spicules. Spicules trapped into the network of rhizomes progressively buried, named “matte”, represent a sedimentary sequence interpretable on a temporal scale. By means of a vertical corer we collected samples of sediment at 0.5, 1, 1.5 and 2 m depth along the matte profile in order to quantify the amount of biogenic silica used to assess past dynamics of the sponge community in four P. oceanicameadows of the Ligurian sea. The content in biogenic silica was determined by spectrophotometric analysis of the sediments. While at Prelo Bay the values are constant in the core sample, a general decreasing trend with depth was observed in the meadows of Punta Pedale, while in the site of Punta Manara the major amount of silica was found deeper in the matte. The temporal variations of sponge abundance were probably due to historical anthropogenic factors. In the meadow of Bergeggi, BSi concentrations, significantly lower compared to all other sites, were likely caused from inputs from the close Savona harbor and strong bottom currents avoiding spicule deposition.

AbstractIn the Mediterranean Sea, the two sponges of the genus Aplysina(A. aerophobaand A. cavernicola) are identified on the basis of their external morphology and the environment in which they live. During a research program on the sponge fauna in semi-submerged caves of the Italian coasts, we have sampled an abundant very small yellow sponge, often living in the tidal zone, which were attributed to the genus Aplysina. Failing to assign the samples to a species through classical taxonomic methodologies (growth form and skeleton arrangement) and for the particular environment where this sponge lives, we have decided to use the COI analysis to solve the taxonomic problem offered by these miniaturized specimens. The analysis indicated that, in spite of the morphological differences, they belong to A. aerophoba. During old detailed surveys, conducted in the ’60 years in some of the studied caves, this species was not recorded. It is possible that its abundant presence is related to the modifications occurred in the Mediterranean sponge communities occurred in the last decades in relation to global warming.

AbstractA rapid temperature increase in the 1980-90s has been accompanied by dramatic and unprecedented changes in the biota and communities of the Ligurian Sea. This review uses existing historical series (a few of which have been purposely updated) to assess extent and consequences of such changes. A number of warm-water species, previously absent or occasional in the comparatively cold Ligurian Sea, has recently established thanks to warmer winters. Occurrence among them of invasive alien species is causing concern because of their capacity of outcompeting autochthonous species. Summer heatwaves, on the other hand, caused mass mortalities in marine organisms, some of which found refuge at depth. New marine diseases appeared, as well as other dysfunctions such as the formation of mucilage aggregates that suffocated and entangled benthic organisms. Human pressures have combined with climate change to cause phase shifts (i.e., abrupt variations in species composition and community structure) in different habitats, such as the pelagic environment, seagrass meadows, rocky reefs, and marine caves. These phase shifts implied biotic homogenization, reduction of diversity, and dominance by invasive aliens, and may be detrimental to the resilience of Ligurian Sea ecosystems. Another phase of rapid warming has possibly started in the 2010s and there are clues pointing to a further series of biological changes, but data are too scarce to date for proper assessment. Only well addressed long-term studies will help understanding the future dynamics of Ligurian Sea ecosystems and their possibilities of recovery.

AbstractSettlement, 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, Chthamalusspecies 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 Chthamalusspecies 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.

AbstractVelella velella, the so-called by-the-wind sailor, is a common member of the open-ocean pleustonic fauna, worldwide distributed in tropical and temperate regions. Thanks to their sail protruding above the sea surface, floating polymorphic colonies of this hydrozoan are carried by winds, and tend to aggregate in large swarms, that often get stranded along the shores. Although these events are commonly observed in springtime along the Ligurian coasts (North-western Mediterranean Sea), no quantitative characterization was ever made. The aim of this study was to characterize the stranding events that occurred in spring 2016 along the Ligurian coast, by evaluating the influence of the local sea conditions and by quantifying the abundance of the stranded colonies in each event. Their size-frequency distribution and biomass were examined, and the associated mollusc fauna identified and counted. The magnitude of these episodes was so relevant that, along the Ligurian coasts, the V. velellastrandings constitute one of the most important biological deposition of organic matter; nevertheless, the ecological role of these remarkable and stochastic accumulations of chitin along the coast is still unexplored.

AbstractStylasterids belong to one of the few calcifying hydroid families that are commonly found in shallow tropical coral reefs. Although these corals are accurately described from a taxonomic point of view, information about their ecology is scarce. Distichopora violaceais one of the most common stylasterids of the Indo-Pacific region; however, no information is yet available on its distribution and abundance. To fill this gap data we gathered data during three scientific expeditions on four Maldivian atolls. In each atoll investigations were carried out at three depths, both in the ocean and in the lagoon reef, to examine differences in colony density and distribution. Distichopora violaceawas observed in all the studied atolls; however, its distribution and density were not homogeneous among them. This species was more abundant in the ocean reefs than in the lagoon ones, suggesting a strong influence of water movement. Moreover, we found a high variability in colony density in the eastern ocean reefs that was tentatively attributed to a different topography of the reef: colonies were more abundant on the gentle slopes of Malè atolls than on the steep reefs of Felidhoo. Oceanographic features, mainly due to the seasonal monsoons, are likely to interact with the biological requirements of the species in determining the observed asymmetrical geographical distribution. The present investigation provides new insights on the stylasterid D. violaceaand, for the first time, quantitative data on its distribution and density that can be useful for conservation and management of this CITES regulated species.

AbstractIn 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.

AbstractAn 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−2was 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. sarmentosawere 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.

AbstractDuring spring 2017, starting from 12 May, exceptional strandings of the purple snail Janthina pallidawere 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−2densely packed with hydrozoan Velella velellasails), 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. pallidabanks 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.

AbstractTwo shallow hydrothermal vents were investigated by SCUBA diving to evaluate their influence on the structure and diversity of a sponge community living close to the vent outflow, in the equatorial Pacific Ocean just off the coast of North Sulawesi, Indonesia (1°40.361ʹN, 125°8.112ʹE). No sponges identified were vent-obligate species, since they are found in the surrounding coral reefs too. The sponges were strongly attracted by the vent, concentrating in an area of a few meters around it, where they reached covering values up to 70% in the deeper vent and up to 42% in the shallower one. The high silica concentration, 8.5 mg L−1Si (deep vent) and 5 mg L−1Si (shallow vent), in hot spring water (90°C) was the putative environmental factor driving the sponge settlement and growth. These organisms take advantage of the increased silica availability that, facilitating skeleton formation, probably promotes sponge growth. This hypothesis is in agreement with the evidence that the spicules of the sponge specimens living around the hot springs have a thickness about double that of conspecific specimens present on the coral reefs at least 300 m away.

Scanning electron microscopy (SEM) investigation of two Antarctic sponges, Phorbas glaberrima and Tedania charcoti, showed that the exopinacoderm effects a direct uptake of benthic diatoms which settle on the sponge surface. In P. glaberrima, planktonic diatoms were also observed penetrating through the inhalant system, the primary way of feeding in sponges. Benthic diatoms which accumulate in the mesohyl underneath the exopinacoderm help to strengthen the sponge cortex and may be an alimentary source during oligotrophic periods in the Antarctic environment.

Summary: The biogeography of Antarctic demosponges has been studied by dividing Antarctic and circumantarctic areas into geographic entities, and then assigning to these entities all recorded species according to literature reports. Correspondence analysis ordination based on the presence or absence of species shows the existence of a distinct Antarctic Faunistic Complex (AFC), including continental Antarctica, most of the Antarctic and circumantarctic islands and the Magellan area. Such a result has enabled us to drawup a checklist of 352 Antarctic demosponge species. Investigation of within-AFC patterns indicates that the continent is a highly homogeneous area, establishing closer relationships with the Scotia Arc and to a lesser extent with the Magellan region. The AFC has low specific affinities with the other circumantarctic regions (South Africa, temperate Australia and New Zealand), whereas at the generic level relationships appear more pronounced. This biogeographic pattern may lead us to suppose a common Gondwanian origin for Antarctic and circumantarctic sponge faunas, followed by differentiation due to Gondwana fragmentation. Antarctica moved towards polar latitudes and became progressively isolated, only maintaining active interchanges with South America. Climatic changes possibly induced intense processes of speciation in the Antarctic demosponge fauna, thus contributing to its differentiation.

Two new steroidal derivatives, named clionastatins A and B, have been isolated from the burrowing sponge Cliona nigricans. These molecules are tri-and tetrachlorinated androstane derivatives, respectively, and they represent the first polyhalogenated steroids found in a natural organism, either marine or terrestrial, and the first examples of halogenated androstanes in nature. Both clionastatins proved to be potently cytotoxic.