Eastern Ligurian Sea Research Articles

Unveiling near-inertial wave dynamics and storm-driven currents: Insights from moorings in the coastal Mediterranean Sea

This study presents comprehensive observations of currents and seawater properties (temperature, salinity and density) made with moored instruments on the continental slope in the eastern Ligurian Sea (Mediterranean) between 18 October and November 6, 2021. During this period, the depth of the surface mixed layer increased from 40 to 70 m. At the same time, near-inertial waves were consistently observed below the mixed layer. In particular, on 28 October, a depression in the mixed layer depth triggered the formation of a pronounced wave packet. This packet radiated downwards between 70 and 200 m and propagated southward. The wave packet had a vertical and horizontal wavelength of about 80 m and 150 km, respectively, an upward vertical phase speed of 100 m/d, a downward vertical group speed of 10–15 m/d, and a downward energy flux of 0.2–0.3 mW/m2. The observed frequency appeared subinertial, likely due to the red-shifting of the effective inertial frequency by the background vorticity. From 1 November, a storm with wind speeds of up to 15 m/s prevailed in the region. Near-inertial motion was pronounced throughout the water column and manifested itself as a first baroclinic mode. This mode exhibited a maximum isopycnal vertical displacement in the thermocline, accompanied by oscillatory currents that reversed with depth. Mainly superinertial currents were observed. The temperature and velocity data collected from all moorings indicated a southwestward propagation with a horizontal wavelength of about 200 km. While a slab model was partially successful in predicting inertial currents in the surface mixed layer, the storm-induced dynamics presented a challenge that was beyond the scope of the model.

High Megabenthic Complexity and Vulnerability of a Mesophotic Rocky Shoal Support Its Inclusion in a Mediterranean MPA

The deep shoal of Punta del Faro (Ligurian Sea, Mediterranean Sea) is a mesophotic rocky elevation hosting complex animal forests threatened by fishing activities. To identify appropriate conservation measures and set a reference example for similar cases, we present a detailed characterization of its megabenthic communities and a quantification of the fishing pressure. The results highlight the high natural value of the area, presenting high biodiversity (111 megabenthic and demersal species) and diverse types of animal forest, predominantly dominated by cnidarians. The tridimensional seascape is among the most complex in the eastern Ligurian Sea, but the long-term evaluation of its environmental status suggested consistent affects due to the high abundance of lost fishing gear (0.65 items m−2) directly entangled with structuring cnidarians. The artisanal and recreational fishing pressure are currently moderate. However, the use of bottom-contact fishing gear causes significant modifications to the seafloor’s integrity. This study emphasizes the high conservation value and vulnerability of the shoal, highlighting the importance of its protection through its inclusion in the Portofino MPA, whose external perimeter is 200 m from the study area. A critical discussion of the advantages and disadvantages is provided with a map of the possible extension of the MPA boundaries.

The cold-water coral province of the eastern Ligurian Sea (NW Mediterranean Sea): historical and novel evidences

Several bathyal cold-water coral provinces, characterized by a lush growth of habitat-forming scleractinians, have been recognized in the Mediterranean Sea. However, the search for this biogenic habitat only marginally targeted the Italian coast of the Ligurian Sea (NW Mediterranean basin) despite historical and a few recent local studies in the region reporting the presence of corals. This study used bathymetry maps, side-scan sonar profiles, historical charts, and trawling routes to identify sites that could potentially host coral habitats in the eastern sector of the Ligurian Sea. Remotely operated vehicle video footage from various projects (2015-2021, 20 dives) was then used to characterize four sub-areas (Genoa Plateau, Portofino, Deiva Marina, and Monterosso) where corals were detected between 450 m and 750 m depth. Radiocarbon dating was used to trace back the geological history of the coral structures. A small coral mound, impacted by trawling activities, was found on the Genoa Plateau, while four massive coral structures were found in the other sub-areas, mainly located in a morphologically complex and highly energetic canyon region. High levels of megafaunal biodiversity, including rarely reported alcyonaceans as Placogorgia coronata, were observed together with moderate fishing impact. Overall, the identified coral areas potentially account for 9 km2 of both subfossil mounds (as old as 13300 years BP), dominated by Desmophyllum pertusum, and living reefs, dominated by Madrepora oculata, the latter representing up to 23% of the substrate coverage. The few living colonies of D. pertusum in the area represent the first documented records for the Ligurian Sea. These data support the presence of a distinct eastern Ligurian cold-water coral province.

Deep-water hydrodynamic observations around a cold-water coral habitat in a submarine canyon in the eastern Ligurian Sea (Mediterranean Sea)

Abstract. A 2-year dataset of a stand-alone mooring, deployed in November 2020 down the Levante Canyon in the eastern Ligurian Sea, is presented. The Levante Canyon Mooring (LCM) is a deep submarine multidisciplinary observatory positioned at 608 m depth in a key ecosystem area. The Levante Canyon hosts a valuable and vulnerable ecosystem of deep-living cold-water corals (CWCs), studied and monitored since 2013 through integrated mapping of the seabed and water column. The 2-year dataset, acquired on the mooring and presented here (data from November 2020 to October 2022), includes measurements conducted with both current meters and conductivity–temperature–depth (CTD) probes and provides information about the hydrodynamics and thermohaline properties across almost the entire water column. The observatory is still ongoing, and the dataset is regularly updated. All the described data are publicly available from https://doi.org/10.17882/92236 (Borghini et al., 2022). They must therefore be preserved and are of considerable scientific interest.

Population structure change in a temperate reef coral after a quarter of century

Seawater warming is affecting corals worldwide. Mass mortality events are increasingly frequent, and the bioconstruction potential of coral reefs is jeopardized. Revisiting sites surveyed in the past may represent a valuable tool to better understand the health state and ongoing trend of coral reefs. In the Mediterranean Sea the only reef-building coral is the endemic species Cladocora caespitosa. Several mortality events of this coral, due to thermal anomalies, have been reported in the last decades. An impressive change occurred in a population of C. caespitosa revisited 25 years after: smaller colonies became the prevalent size class and larger colonies disappeared, highlighting a loss in the bioconstruction potential. Data collected on C. caespitosa colonies in the Eastern Ligurian Sea (NW Mediterranean) revealed that mortality rate was correlated with colony size, while reproductive potential apparently increased, suggesting hormesis (i.e., enhanced reproductive output under pre-lethal conditions).

Signature whistles of the demographic unit of bottlenose dolphins (Tursiops truncatus) inhabiting the Eastern Ligurian Sea: characterisation and comparison with the literature

Bottlenose dolphins (Tursiops truncatus) make extensive use of narrowband whistles with individually distinctive frequency modulations to broadcast their identity: the signature whistles. The acoustic structure of the signature whistles tends to be stable over decades. Therefore, these vocalisations have the potential to be used for monitoring individuals over time. Our study investigated the acoustic structure of the signature whistles of the demographic unit of bottlenose dolphins inhabiting the Eastern Ligurian Sea (Italy), within the Pelagos Sanctuary. Through visual categorisation of spectrograms, we identified 941 whistle contours, 469 of them were classified as signature whistles using the SIGnature IDentification (SIG-ID) method. We further grouped these into 19 different categories based on their stereotyped frequency modulation patterns. To support our categorisation, we used a combination of a visual classification task conducted by six naïve judges and an automated analysis, the principal component analysis. Overall, this study characterises the signature whistles of the demographic unit of bottlenose dolphins inhabiting the Ligurian Sea for the first time. Furthermore, when comparing the acoustic features of these whistles with those of other different demographic units available from the literature, we observed differences in the values of the minimum and maximum frequencies. Considering the critical vessel traffic of our study area, we interpreted these variations in light of the high levels of anthropogenic noise. We recommend further investigations to understand the mechanisms underpinning the acoustic variation of bottlenose dolphins’ signature whistles and to elaborate effective management and protection policies for this species.

Aspects of the summer circulation in the eastern Ligurian Sea

Water exchanges between the Tyrrhenian Sea and the Liguro-Provençal basin occur through the Corsica Channel, a narrow passage between Corsica and the Elba Island, near the Italian coast. It has long been known that the Channel hosts a robust Tyrrhenian outflow in winter, which penetrates far into the Ligurian Sea, reaching the site where deep-water formation takes place. The summer circulation in the area, and, more generally, in the eastern part of the Ligurian Sea, is less well known. Several experimental and modelling works in the last decade have pointed out the presence of an anticyclone in the Channel area, sometimes referred to as Ligurian anticyclone, which could modulate the exchanges between the two basins in summer, and could strongly affect the dispersion properties in the south-eastern Ligurian Sea, with implications on the local, delicate marine environment. In this work, we focus on this structure, and on the role it plays in the local circulation, seeking information from long datasets of satellite observations (sea level, sea surface temperature and turbidity) that are now available. We find that the Ligurian anticyclone is a recurrent feature of the local circulation in summer. Its core is located between Cap Corse (the peninsula at the northern end of Corsica) and the Elba Island, but the anticyclone may extend till the Italian coast, and it may sometimes be more elongated in the latitudinal direction, and/or more displaced towards north. In some years, a companion anticyclonic vortex is found more to the north, in the north-eastern portion of the Ligurian Sea, but the robustness of this structure is unclear. Analysis of the ERA5 winds indicates that the Ligurian anticyclone is likely driven by an area of negative wind stress curl usually present near Cap Corse in summer, even though contributions from the surrounding circulation cannot be a priori excluded.

A numerical investigation for dating 210Pbex and 137Cs vertical profiles in a coastal area: The Eastern Ligurian Sea, Italy

210Pb and 137Cs vertical profiles in coastal sediments are studied using a sedimentation-mixing model. The cores were sampled in a complex coastal area characterized by the presence of different impact sources and environmental uses (riverine inputs, commercial and military harbour, marine protected area) in the Eastern Ligurian Sea, Italy. The analysis of accumulation and dispersion processes is performed using a numerical advection and diffusion model, in terms of the independent variables - time and mass depth. The flux of 210Pb is considered in steady state while the time dependent input flux of 137Cs is estimated from the concentration of this radionuclide in seawater, starting from observed data from 1960 to date. Differently from the atmospheric fallout distribution, this input function contains, at least partly, the contribution that still continues to reach the sediment in the last 25 years as a result of coastal and riverine input. The analysis highlights some features obscured in experimental data, and allows comparison of the effects of different scenarios. The specific effect of a pulsed input is discussed by analysing the effects of the Chernobyl event. The effects of mass flux in non–steady state are also considered: we observe that since the pulsed inputs in 137Cs are now too old, a strong superficial mixing and a time-variable flux produce similar profiles for both radionuclides. Hence, the general environmental knowledge of the area remains the main instrument to fully define the active processes in some cores.

Understanding altimetry signals in the Northeastern Ligurian sea using a multi-platform approach

During the Long-Term Glider Mission for Environmental Characterization 2016 sea trial, carried out in the eastern Ligurian Sea (Northwestern Mediterranean Sea), two gliders rated to a maximum depth of 1000 m operated continuously from 3 May 2016–27 June 2016. When possible, glider tracks were synchronized with the contemporaneous footprints of the Jason-2, SARAL/AltiKa and CryoSat-2 altimeters. Temperature and salinity measured by the gliders that were co-localised with the altimeter passages were used to calculate along-track dynamic heights (DH). The latter were then compared with the altimeters’ near real-time absolute dynamic topography (ADT) measurements. ADT and DH values showed very similar, but shifted patterns, suggesting that gliders had sampled the same structures but at different times. Average surface absolute geostrophic velocities at the time of glider transit were used in a novel relocation technique to reposition glider measurements where they would have been at the time of the altimeter passage. The relocation increases the correlation between datasets to a value close to 1 and reduces the RMSE of an order of magnitude, also when the time-difference between measurements was greater than 3 days. The sea level spatial and temporal variability is attributed to the presence of meanders generated by the baroclinic instability of the Liguro- Provençal Current (LPC). These meanders are characterized by a 38 km amplitude and 0.12 m s−1 average propagation speed that are confirmed by the larger scale ocean colour measurements and are in agreement with those previously described in the literature. We found that the presence of LPC meanders in along-track ADT and DH measurements is evidenced by a decrease in sea level when profiles sampled the Modified Atlantic Water, and an increase in sea level when measurements sampled the adjacent waters of Tyrrhenian Sea origin. The relocation technique introduced here is expected to improve future altimetry-glider comparisons, as similar validation experiments were considered possible only when glider and altimetry measurements were near synoptic, and collected up to one day from each other.

Benthic foraminifera in a coastal marine area of the eastern Ligurian Sea (Italy): Response to environmental stress

Benthic foraminiferal assemblages from 19 superficial marine sediment samples of a coastal area in the Ligurian Sea were analysed for benthic foraminifera in order to recognize changes in assemblage composition and structure, decrease of faunal density, increased morphological abnormalities and inclusion of heavy metals in carbonate tests as possible evidences of environmental stress. Also grain size was determined as a main factor conditioning foraminifer’s distribution.The generalized low faunal density was considered as indicative of environmental stress, attributable to the well-known natural Cr and Ni enrichment, which characterizes marine sediments of the region. The cluster analysis highlighted distinct foraminiferal assemblages with decreasing species diversity approaching to the coast. This distribution was interpreted as the result of local source of environmental stress, probably due to the stream contribution. Deformed foraminifera more abundant than background levels of unstressed environments were also recorded in 39% of samples.Energy Dispersive Spectroscopy (EDS) analyses were carried out on carbonate tests of 55 specimens to investigate the role of the incorporation of heavy metals in the development of morphological abnormalities. Foraminifera showed the inclusion of heavy metals, not present in control specimens, indicating that environmental stress, due to metal sediment enrichment, plays a role in this phenomenon. Although anomalous elements were detected both in normal and deformed specimens and chambers, it was supposed that deformities develop as a result of the toxic effect of heavy metals on cytological activities because, contrarily to the normal specimens, all the deformed ones included anomalous elements. Higher occurrence of deformities in porcelaneous tests, typically enriched in Mg, is associated to the higher number of incorporated elements (Mn, Fe, Cu and Zn).

Uncertainty evaluation of CTD measurements: a metrological approach to water-column coastal parameters in the Gulf of La Spezia area

The ENEA Marine Environment Research Centre of S. Teresa has been involved since the ‘70s in monitoring, analysis and comprehension of physical, chemical and biological processes in marine environment. The purpose of this work is to describe the recently-implemented metrological approach aimed at evaluating the uncertainty associated with measurements performed by a Conductivity-Temperature-Depth profiler (CTD) during routine coastal campaigns in the Eastern Ligurian Sea, close to the Gulf of La Spezia. Main effort of this work is focused on applying, to each involved parameter, the standard framework for uncertainty evaluation as prescribed by the Guide to the expression of uncertainty in measurement. To this aim, an appropriate uncertainty evaluation is performed by combining type A and B contributions, evaluated from experimental data obtained in reproducibility conditions and from calibration certificates periodically supplied by manufacturer, respectively. Concerning in situ measured practical salinity, probability density functions modelling water pressure, temperature and conductivity, from which salinity depends, are propagated by application of the Monte Carlo method for propagation of distributions, hence obtaining the salinity uncertainty.

Cold‐water coral Madrepora oculata in the eastern Ligurian Sea (NW Mediterranean): Historical and recent findings

Abstract Cold‐water coral (CWC) ecosystems are long‐lived, slow‐growing and fragile, which makes them especially vulnerable to physical damage. In recent decades, CWCs have been severely threatened by fisheries, hydrocarbon extraction, pollution and other human activities. In the Mediterranean Sea, some investigations have been carried out on CWC ecosystems, mostly focused on their distributions within the central and eastern basins. Historical reports and fishermen's maps for the eastern Ligurian Sea (NW Mediterranean) from the 1960s document the occurrence of extensive banks of living CWC, mostly Madrepora oculata, between depths of 200 and 500 m. In 2013/2014, multibeam, side scan sonar (SSS) and remotely operated vehicle (ROV) surveys were carried out in that area, specifically in the Levante Canyon, to assess the occurrence, distribution and conservation status of CWC. The SSS and ROV showed numerous trawl tracks and small (10 cm high), dead, buried colonies at 300–500 m. Deeper, between 525 and 575 m, dense populations of living, 1 m high colonies of Madrepora oculata were found on the flanks of Levante Canyon. The deep sites showed colonies overturned or entangled by long‐line fishing activities. The discovery of new CWC banks not yet heavily damaged by fishing activities, suggests that urgent measures for conservation should be taken in the Mediterranean and worldwide. The present limitation of trawl‐fishing to above 1000 m depth, established by the General Fisheries Commission for the Mediterranean (GFCM) in 2005, seems to be ineffective, since CWCs are mostly located at less than 1000 m depth in the Ligurian Sea. A network of high‐seas/deep‐sea marine protected areas (MPAs) would favour a better strategy for protecting substantial areas of CWCs.

Demography of the bottlenose dolphin Tursiops truncatus (Mammalia: Delphinidae) in the Eastern Ligurian Sea (NW Mediterranean): quantification of female reproductive parameters

The reproductive histories of 41 adult bottlenose dolphin females were analysed using photo-identification data collected between 2006 and 2014 in four sub-areas of the eastern Ligurian Sea (northwest Mediterranean). The Rapallo sub-area revealed the highest (highly significant) frequency of encounters (per unit effort) of reproductive females in association with young individuals, therefore emerging as a candidate nursery area in the region. The estimated fertility rate of adult females ranged between 290 and 407 births per 1000 individuals per year, higher than that of other known bottlenose dolphin populations, with a calving interval between 2.45 and 3.5 years. These results will be useful for projecting future trends of this (sub)population.

Dissolved organic matter dynamics in surface waters affected by oil spill pollution: Results from the Serious Game exercise

Dissolved organic carbon (DOC), chromophoric and fluorescent dissolved organic matter (CDOM and FDOM, respectively) surface distribution was studied during the Serious Game exercise carried out in the Eastern Ligurian Sea, where an oil spill was localized by using satellite images and models. This paper reports the first DOC, CDOM and FDOM data for this area together with an evaluation of fluorescence as a fast and inexpensive tool for early oil spill detection in marine waters. The samples collected in the oil spill showed a fluorescence intensity markedly higher (~5 fold) than all the other samples. The excitation–emission matrixes, coupled with parallel factor analysis (PARAFAC), allowed for the identification in the FDOM pool of a mixture of polycyclic aromatic hydrocarbons, humic-like and protein-like fluorophores.

Reprint of “Monitoring of a Posidonia oceanica bed (Punta Manara, Eastern Ligurian Sea, Italy) and the associated molluscs twenty years after: What's new?”

This research project by the Marine Biology Laboratory at Turin University determined the degree of conservation and measured the size of the Posidonia oceanica bed in the eastern Ligurian Sea off Punta Manara in 1985–1986, a bed that had also been examined in 1973. This project assessed the structure, dynamics, and organization of the foliar stratum malacofauna in relation to the most important space–time variables, the bathymetric gradients, and the seasons. In 2006 the laboratory investigated this bed with methods like the previous ones in order to evaluate the effect of anthropogenic disturbances and to assess any changes in the P. oceanica and mollusc-community dynamics. Our overall project has spanned many years, something unique in P. oceanica studies. Our structural analysis of the meadow found (i) a reduction in shoot density in all the bed's regions, particularly in the shallow and intermediate belts; (ii) a progressive reduction of the lower limit (now considered erosive–regressive). We sampled the foliar stratum molluscs using hand-towed nets, the means we used to collect semi-quantitative data. In 2006, there were 40% fewer specimens and 31.5% more species than in 1985–1986. The core-stock (sensu Russo) has remained the same over the years in terms of both the presence and the abundance of species (8 dominant species belonging to Cerithidae and Rissoidae). As in 1985–1986, Bittium latreillii is the dominant species, whose juveniles exhibited similar settlement dynamics on the foliar strata and whose samples had comparable peaks in reproduction and abundance. The multivariate approach was applied to both the 1985–1986 and the 2006 data set. The present results confirm those obtained through the Detrended Correspondence Analysis (DCA) in 1985–1986. Namely, time (the period or the season) is the main factor of variability, the one that influences the malacological assemblages the most. The composition of the stocks depends closely on the sampling period (ANOSIM, R=0.532, P<0.001) and hence is linked to the biological cycle of the seagrass. The development of P. oceanica affects the malacological assemblages and regulates them quantitatively, something most evident in the reproductive and settlement cycles of the two dominant families, Cerithidae and Rissoidae. Thus the spatial variations (the variations in depths or bathymetric gradient) play a major role in determining the species of the stocks, while the temporal variations – the changes in seasons – play a major role in determining the total number of molluscs.

Long-term trend in substratum occupation by a clonal, carbonate bryozoan in a temperate rocky reef in times of thermal anomalies

Studies over time provide opportunities to detect variations in the spatial and temporal patterns of clonal organisms and measure changes on their population dynamics related to extreme events. We assessed population dynamics for a bryozoan species dominating a subtidal rocky reef at Tino Island, in the eastern Ligurian Sea (NW Mediterranean). Using 9 years of annual photosurveys (1997–2005), rapid decline in Pentapora fascialis colony cover was shown at 11 and 22 m depths following the anomalous warming events in 1999 and 2003. An 86 % reduction in live colony portion was found after the 1999 warming event (2.3 °C higher than normal), with larger colonies being most affected. Effects from the 2003 event were delayed, and gradual cover decline occurred during the following 2 years. At the “Shallow” photostations, none of the larger colonies (>1,000 cm2) survived after the first cover decline. Availability of new substrate after the 1999 disturbance resulted in enhanced recovery through new colony production. At the “Deep” photostations, the population structure did not change over the duration of the monitoring period showing the same monomodal structure and same dominant size class (50–500 cm²). In the 4 years following the first cover decline, the deeper population regained colony cover to levels similar to pre-disturbance level, showing a good resilience. This 9-year monitoring analysis provided the temporal resolution needed to detect changes occurring in the P. fascialis population and will contribute to the assessment of long-term changes on benthic populations suffering during recent decades from dramatic increases in extreme events.

Granulomatous lesions in a wild mullet population from the eastern Ligurian Sea (Italy): mycobacteriosis vs . pseudotuberculosis

Mycobacterium spp. and Photobacterium damselae subsp. piscicida are recognized as the most frequent causative agents of granulomatous lesions in fish. Although frequent episodes of mycobacterial infections have been reported in wild fish worldwide, only sporadic cases have been documented to date in Italy. To investigate for the presence of lesions referable to mycobacteriosis and to identify the mycobacterial species involved, a total of 159 wild mullets were fished from the eastern coast of the Ligurian Sea, killed and necropsied. Liver and spleen samples were collected from all fish for histopathological and microbiological analyses. Molecular investigations for identification of Photobacterium damselae subsp. piscicida were performed. Gross examination revealed granulomatous lesions in one animal; microscopically, 42.14% of fish displayed granulomas with various histological features, 19.50% resulted positive at Ziehl-Neelsen staining, and were confirmed as mycobacterial lesions by culture. The identified colonies were characterized as M.fortuitum, M.abscessus, M.flavescens, M.chelonae, M.septicum and M.nonchromogenicum. In all, 35% of animals resulted positive for Photobacterium damselae subsp. piscicida. These data suggest widespread mycobacterial infection also by Photobacterium damselae subsp. piscicida infections in wild fish. Moreover, the pathogenicity of some mycobacterial species, previously considered as saprophytic, was demonstrated.

The use of otolith microchemistry to investigate spawning patterns of European anchovy: A case study in the eastern Ligurian Sea (NW Mediterranean)

Spawning patterns of European anchovy were investigated in the eastern Ligurian Sea (NW Mediterranean) by using otolith microchemistry. Otolith cores of 1-year-old anchovies showed a homogeneous chemical composition, while those of 2 years old anchovies separated into five different groups. This suggests the occurrence of single vs. multiple spawning areas related to the two annual cohorts. Patterns of core microchemistry of 2 years old anchovies support the hypothesis of different spawning areas, possibly characterised by different salinity regimes, in the eastern Ligurian Sea (e.g. typical marine habitats like shelf edges vs. lower salinity locations like river mouths). Results suggest that: (1) stocks of European anchovy could depend on different spawning areas characterised by different environmental conditions; (2) patterns may change from year to year, and this could affect the annual risk of stock fluctuations or collapse; and (3) the use of otolith microchemistry is a promising approach for investigating spawning patterns of European anchovy.

Posidonia oceanica meadows as sponge spicule traps

A quantitative study on the sponge spicules present in a series of horizontal core samples, taken at different levels, from a 1.5 m thick living matte within the Posidonia oceanica meadow of Prelo Bay (Eastern Ligurian Sea), has been performed. Sponge spicule amounts were evaluated by microscopical and chemical analyses. From the superficial samples the spicule number decreased until 60–80 cm depth to increase progressively until the deepest studied layer, 140 cm depth. The same results were obtained from the trend of spicule volume and biogenic silica tested by chemical analysis. Among the recognisable spicule types, the most common are oxeas, followed by tylostyles, achantostyles and strongyles. However, oxeas, tylostyles and achantostyles showed the same trend of the entire spicule population, whereas strongyles had an opposite trend with a maximum value at the 80–100 cm depth. According to the hypothesis that the amount of spicules in the sediment is proportional or at least related to the sponge biomass existing in the surrounding area, our data suggest that the sponge assemblage of Prelo Bay should not have been constant in the past 100–200 years. Our hypothesis is that the rapid urban and industrial development that occurred along the Ligurian coast after the Second World War, particularly in the 1960s, had an important impact on the sponge assemblages of the area.

Monitoring of a Posidonia oceanica bed (Punta Manara, Eastern Ligurian Sea, Italy) and the associated molluscs twenty years after: What's new?

This research project by the Marine Biology Laboratory at Turin University determined the degree of conservation and measured the size of the Posidonia oceanica bed in the eastern Ligurian Sea off Punta Manara in 1985–1986, a bed that had also been examined in 1973. This project assessed the structure, dynamics, and organization of the foliar stratum malacofauna in relation to the most important space–time variables, the bathymetric gradients, and the seasons. In 2006 the laboratory investigated this bed with methods like the previous ones in order to evaluate the effect of anthropogenic disturbances and to assess any changes in the P. oceanica and mollusc-community dynamics. Our overall project has spanned many years, something unique in P. oceanica studies. Our structural analysis of the meadow found (i) a reduction in shoot density in all the bed's regions, particularly in the shallow and intermediate belts; (ii) a progressive reduction of the lower limit (now considered erosive–regressive). We sampled the foliar stratum molluscs using hand-towed nets, the means we used to collect semi-quantitative data. In 2006, there were 40% fewer specimens and 31.5% more species than in 1985–1986. The core-stock (sensu Russo) has remained the same over the years in terms of both the presence and the abundance of species (8 dominant species belonging to Cerithidae and Rissoidae). As in 1985–1986, Bittium latreillii is the dominant species, whose juveniles exhibited similar settlement dynamics on the foliar strata and whose samples had comparable peaks in reproduction and abundance. The multivariate approach was applied to both the 1985–1986 and the 2006 data set. The present results confirm those obtained through the Detrended Correspondence Analysis (DCA) in 1985–1986. Namely, time (the period or the season) is the main factor of variability, the one that influences the malacological assemblages the most. The composition of the stocks depends closely on the sampling period (ANOSIM, R=0.532, P<0.001) and hence is linked to the biological cycle of the seagrass. The development of P. oceanica affects the malacological assemblages and regulates them quantitatively, something most evident in the reproductive and settlement cycles of the two dominant families, Cerithidae and Rissoidae. Thus the spatial variations (the variations in depths or bathymetric gradient) play a major role in determining the species of the stocks, while the temporal variations – the changes in seasons – play a major role in determining the total number of molluscs.