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Global climate change has increased the frequency and intensity of extreme heat anomalies and consequent mass coral bleaching events. Long‐term dynamics of hard coral cover, bioconstruction potential, carbonate deposition, and reef accretion was monitored over a 20‐year period on Maldivian coral reefs in order to investigate the effects of high‐temperature anomalies on coral reef accretion and their recovery potential. Changes experienced by shallow reefs between 1997 and 2017 were evaluated by considering five different bioconstructional guilds and the BioConstruction Potential index (BCP), a proxy for the constructional capacity of reefs. Abnormally high temperatures in 1998 and 2016 led to severe coral bleaching and consequent mortality, especially of the primary builders. Renewed carbonate deposition was not documented until 2–3 years after the bleaching, and 6–9 years passed until constratal (i.e., low relief) growth was achieved. Finally, 14–16 years were required to reach accretion rates high enough to ensure superstratal (i.e., high relief) growth. Coral mortality in the Maldives during the 2016 bleaching event was lower than in 1998, and the initial recovery was faster and occurred via a different trajectory than in 1998. Rising levels of anthropogenic carbon emissions are predicted to accelerate sea level rise and trigger severe coral bleaching events at least twice per decade, a frequency that will (a) prevent coral recovery, (b) nullify reef accretion, and consequently, (c) result in the drowning of Maldivian reefs under the worst climate projections. Long term dynamics of hard coral cover, bioconstruction potential, carbonate deposition, and reef accretion were monitored over a 20‐year period on Maldivian coral reefs in order to investigate the effects of high‐temperature anomalies on coral reefs and their recovery potential. Abnormally high temperatures in 1998 and 2016 led to severe coral bleaching and consequent mortality, especially of the primary builders. Renewed carbonate deposition was not documented until 2–3 years after the bleaching, 6–9 years passed until constratal (low relief) growth was achieved, and 14–16 years were required to reach accretion rates high enough to ensure superstratal (high relief) growth. [ABSTRACT FROM AUTHOR]

Global climate change is affecting the planet’s biodiversity, altering marine ecosystems and modifying species distributions. Using historical and recently collected data, changes in depth distribution of two hydrozoan taxa (Ectopleura croceaandMilleporaspp.) with different life histories, ecology and geographic distributions were compared to trends in sea surface temperature (SST).Ectopleura crocea, a temperate species, used to be very common in Italian seas on shallow water artificial substrata, where it settled mainly between spring and autumn. In the Maldives, three species of the tropical hydrocoralMillepora(M. platyphylla,M. latifoliaandM. tenera) were reported as common from the early 20th century until recently.Milleporaunderwent mass mortality during a bleaching event linked to a thermal positive anomaly caused by El Niño and lasting from April to July, 1998. Similarly,E. croceadisappeared from Italian surface waters where it was once abundant. Both the temperate and the tropical hydrozoans survived at moderate depth and recolonized shallow water habitats in recent years. These two hydrozoan examples support the depth refugia hypothesis, according to which marine organisms may shift to deeper habitats to avoid shallow water heatwaves and increased temperature variability. Return to shallow water has been possible only after acclimation such as shifting season of occurrence from summer to winter–spring (E. croceain Italian seas) or possibly through species replacement (Milleporain the Maldives). Continued field research is needed to understand and evaluate the effect of climate change on marine species distribution. [ABSTRACT FROM PUBLISHER]

Coastal urbanization and the consequent proliferation of artificial structures greatly impact rocky reef communities, productive and diverse marine environments that play a crucial role in the functioning of broader coastal ecosystems. This study, conducted along a 7 km stretch of coastline at increasing distance from the port of Genoa (Ligurian Sea), investigated whether the alternating presence of artificial and natural reefs leads to discernible differences in the biota inhabiting these two reef types. The study area is one of the most anthropized areas of the Mediterranean Sea, exhibiting nearly 60% coastal artificialization, which severely impacts coastal ecosystems, favouring the replacement of sensitive species with more tolerant species. Ten reefs (5 natural and 5 artificial) were surveyed by scuba diving at about a 6-m depth, employing quadrats of 50 cm × 50 cm to estimate visually the percent cover of conspicuous sessile organisms. The artificial reefs hosted a similar number of species (18) to their natural counterparts (19) but exhibited a distinct community composition: the former were especially characterized by Jania rubens and filamentous algae, with the latter characterized by Peyssonnelia squamaria and Mesophyllum lichenoides. This difference, however, became negligible where coastal habitat fragmentation (here measured with a purposely devised Fragmentation Index) was minimal. Reducing fragmentation may therefore represent a management strategy to minimize the potential impact of artificial structures on marine biodiversity. [ABSTRACT FROM AUTHOR]

Decapod crustaceans are important components of the fauna of marine caves worldwide, yet information on their ecology is still scarce. Mediterranean marine caves are perhaps the best known of the world and may offer paradigms to the students of marine cave decapods from other geographic regions. This review summarizes and updates the existing knowledge about the decapod fauna of Mediterranean marine caves on the basis of a dataset of 76 species from 133 caves in 13 Mediterranean countries. Most species were found occasionally, while 15 species were comparatively frequent (found in at least seven caves). They comprise cryptobiotic and bathyphilic species that only secondarily colonize caves (secondary stygobiosis). Little is known about the population biology of cave decapods, and quantitative data are virtually lacking. The knowledge on Mediterranean marine cave decapods is far from being complete. Future research should focus on filling regional gaps and on the decapod ecological role: getting out at night to feed and resting in caves during daytime, decapods may import organic matter to the cave ecosystem. Some decapod species occurring in caves are protected by law. Ecological interest and the need for conservation initiatives combine to claim for intensifying research on the decapod fauna of the Mediterranean Sea caves. [ABSTRACT FROM AUTHOR]

Biotic homogenization is an expected effect of biological invasions. Invasive alien species typically show great adaptability to a wide range of environmental conditions and may expand into different habitats, thus reducing the dissimilarity among the recipient communities. We tested this assumption by analyzing a comprehensive database (78 species × 229 samples) collected between 2012 and 2017 in the marine protected area of Portofino (NW Italy), where Caulerpa cylindracea, one of the worst invaders in the Mediterranean Sea, exhibits high substratum cover at depths between 1 m and 45 m in 14 different communities (identified according to the European Nature Information System EUNIS for habitat classification). Five samples for each of the eight depth zones (i.e., 5 m, 10 m, 15 m, 20 m, 25 m, 30 m, 35 m, and 40 m) were randomly re-sampled from the comprehensive database to produce a dataset of 67 species × 40 samples. Then, a second dataset of 66 species × 40 samples was simulated by excluding Caulerpa cylindracea. Both re-sampled datasets underwent multivariate analysis. In the presence of C. cylindracea, the overall similarity among samples was higher, thus indicating homogenization of the rocky reef communities of Portofino Marine Protected Area. Continued monitoring activity is needed to understand and assess the pattern and extent of C. cylindracea's inclusion in the recipient ecosystems. [ABSTRACT FROM AUTHOR]

Global warming is causing poleward expansion of species ranges. Temperate seas, in particular, are undergoing a process known as 'tropicalisation', i.e., the combination of sea-water warming and establishment of southern species. The Ligurian Sea is one of the coldest sectors of the Mediterranean and has thus been characterized by a dearth of warm-temperate species and a comparative abundance of cold-temperate species. This paper uses a time series of sea surface temperature (SST) and new records of thermophilic fish species to reconsider the biogeography of the Ligurian Sea. SST has risen by about 0.7 °C on average between 1948 and 2023, but two phases may be distinguished: a cool one (ended in the mid-1980s) and a warm one (still ongoing); the latter phase shows alternating periods of rapid warming and comparatively stationary temperature. The arrival of thermophilic species coincided with the periods of rapid warming; some of these species were established in the subsequent stationary periods. Heatwaves and climate-related diseases associated with the periods of rapid warming have caused mass mortalities of autochthonous species. Our knowledge on the biogeography of the Ligurian Sea was established during the cool phase; the present situation, however, calls for re-defining the chorological spectrum of the Ligurian Sea biota. [ABSTRACT FROM AUTHOR]

In the Mediterranean Sea, the bivalve genus Pinna is represented by two species: the endemic Pinna nobilis and the (sub)tropical Atlantic Pinna rudis. P. rudis is generally less common and mostly restricted to the warmer regions of the western Mediterranean. However, since a mass mortality event, caused by a pathogen infection, has brought P. nobilis to the brink of extinction, records of P. rudis have increased in several Mediterranean regions, where it had not been previously observed. This paper reports on the presence of several P. rudis individuals in the Ligurian Sea, the northernmost reach of this species in the western Mediterranean. P. rudis has become increasingly common between 2021 and 2023, with a total of 28 new records from seven localities along the Ligurian coast. The size of the individuals and their estimated growth rate (3.6 cm·a−1) indicated that a recruitment event most likely took place in summer 2020, when P. nobilis was no longer present in the area. Our observations suggest that the recruitment success of P. rudis increased following the decline of P. nobilis. However, considering the thermophilic nature of P. rudis, in all likelihood, the ongoing water warming is playing a crucial role in the successful establishment of this species in the Ligurian Sea. A full understanding of the recent range expansion of P. rudis in the Mediterranean is far from being achieved, and whether P. rudis will be able to fulfil the ecological role of P. nobilis is difficult to predict. Large scale monitoring remains the only effective way to know about the future of Pinnids in the Mediterranean Sea. [ABSTRACT FROM AUTHOR]

Highlights • Temperate mesophotic reefs host animal forests vulnerableto fishing activities. • These habitats provide goods for society and their monitoring is of major interest. • A multiparametric index based on ROV footages is herein proposed and tested. • Results show five different environmental status levels for the investigated sites • The MACS index provides a valuable tool to monitor the health of mesophotic reefs. Abstract Temperate mesophotic reefs (circalittoral and offshore circalittoral hard/firm habitats), host complex three-dimensional animal forests and are vulnerable habitats protected by international agreements. In order to evaluate and monitor the environmental status of these ecosystems, the multi-parametric index Mesophotic Assemblages Conservation Status (MACS) was developed, including two independent components, namely Index of Status (I s) and Index of Impact (I i). The I s includes six metrics, targeting conspicuous species diversity, basal layer and canopy composition, whilst the I i is composed by six metrics targeting siltation level, canopy condition and marine litter occurrence. Underwater video transects recorded with a Remotely Operated Vehicle (ROV) along the Ligurian and Tyrrhenian Seas offered the chance to test the index on a large geographic scale and various ecological settings, for a total of 14 sites subjected to different human pressures. MACS index showed a high potentiality to distinguish among a wide range of environmental conditions, with local critical situations mainly related to high fishing pressure. With respect to other existing indices, MACS is based on a larger number of parameters, resulting in a higher ability to disentangle natural and anthropogenic factors, hence it leads to a better interpretation of local situations. This tool represents a contribution to the requirements for the monitoring of these marine environments, set by the EU Marine Strategy Framework Directive, the Habitats Directive, and the guidelines of the Integrated Monitoring and Assessment Programme of the Mediterranean Sea and Coast of the Barcelona Convention. [ABSTRACT FROM AUTHOR]

Abstract Shallow hydrothermal vents emit warm water, carbon dioxide, toxic chemicals, nutrients and reduced compounds that altogether mimic climate and human impacts, and are therefore considered as 'natural laboratories' at which can be investigated the effects of these stressors on marine ecosystems. One of the effects more thoroughly investigated is the impact of reduced pH on marine biodiversity. Calcifying organisms, such as corals, are expected to be more affected, but their response to reduced pH values in seawater has been tackled mostly by laboratory studies. Here, we assessed coral recruitment and juvenile survival, two fundamental processes for coral reef maintenance and resilience, in shallow reefs of North Sulawesi (Indonesia) close to hydrothermal vents. Differences in abundance of coral recruits (<5 cm in diameter) and juveniles (5–15 cm in diameter) were evaluated at vent sites and at control sites, on both reef flats and upper slopes. Recruits of Acropora and other broadcasting corals resulted more abundant near vents, while no difference in juvenile survival was observed between vent sites and controls. On the contrary, Pocillopora , which includes many brooders, showed a low density of recruits and low survival rates at vent sites. Vents caused a typical closed water circulation that retained coral larvae on site, and this effect, rather than water acidification or the emission of chemical compounds, was likely to be responsible for increased recruitment of broadcasters. Graphical abstract Image 1 Highlights • Coral recruitment and survival are not affected by water acidification. • Recruits' abundance is enhanced in vent sites compare to control sites. • Hydrothermal vent cause a closed water circulation. • Vent activity promote coral recruitment by retaining coral larvae. • Broadcast-spawning corals, Acropora and most of the Others, seem to be favoured. [ABSTRACT FROM AUTHOR]

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). • Cladocora caespitosa is the only reef-building coral in the Mediterranean Sea. • C. caespitosa has been affected by mass mortality events due to the water warming. • Evaluation of the present coral health status requires long-term data series. • A loss in the bioconstruction potential of C. caespitosa was observed. • Mortality of C. caespitosa concerns predominantly largest colonies. [ABSTRACT FROM AUTHOR]

The Serpulidae are a large family of sedentary polychaetes, characterized by a calcareous habitation tube, which they cannot leave. The calcium carbonate tube is in the form of both aragonite and calcite, in fairly constant ratio for each taxon. Tubes are cemented firmly to any hard substrate (in only few species tubes are free). Although in the majority of the species the tubes encrust the substrate for all their length, the distal part may eventually detach and grow erectly. Certain species in dense populations build tubes vertical to the substrate in clumps and cement the tubes to each other. This gives serpulids the capability of forming reef-life structures when densely settling. Despite the relative smallness of the individual tubes (rarely longer than 15 cm and wider than 1 cm), such reef-like structures may cover tens of m2, with a layer more than 1 m thick. Serpulid reefs can be divided roughly into seven groups, according to the building modality and the type of habitat they occupy: (i) pseudocolonies; (ii) littoral belts; (iii) subtidal to deep-water reefs; (iv) reefs in coastal lakes and harbours; (v) brackish water reefs; (vi) tapestries in freshwater caves; (vii) biostalactites inside marine caves. The role of serpulid reefs in the ecosystems they inhabit is multifarious and may be distinguished in functions (biomass and production, benthic pelagic coupling, resistance and resilience, reproductive and survivorship strategies, trophodynamics, bioconstruction, living space and refuge, nursery, sediment formation and retention, food for other species, carbonate deposition and storage) and services (water clearance, reef associated fishery, cultural benefits). On the other hand, many serpulids are important constituents of biological fouling, and their calcareous masses damage submerged artefacts, causing huge economic costs. Positive and negative roles of serpulid reefs need to be compared with common metrics; the overall balance, however, is still to be assessed. [ABSTRACT FROM AUTHOR]

This study investigates the bottlenose dolphin (Tursiops truncatus, Montagu 1821) habitat use in the Portofino marine protected area (NW Italy) and adjacent waters, a core area for the dolphins and a highly touristic area in the Mediterranean Sea. A permanent automated real-time passive acoustic monitoring system, able to detect and track dolphins continuously, was tested in the area within the activities of the Life+ Nature project ARION. The habits of bottlenose dolphins was investigated considering the resident rate inside the area, which quantifies the amount of time dolphins spent in these waters, by means of random forest regression. The dependency of dolphin resident rate was analyzed in relation to four explanatory variables: sea surface temperature, season, time of day, and proximity to the coast. Dolphins spent more time in the area during spring and when sea surface temperature ranged between 15–16°C. Summer resulted the season with lower dolphin residency with significant difference between working day and weekend, in the last the lowest residency was recorded. Main findings provide important information to properly manage the area in order to protect bottlenose dolphins. [ABSTRACT FROM AUTHOR]

Marine caves are unique and vulnerable habitats threatened by multiple global and local pressures. Changes in the sessile epibenthic community of the Grotta Azzurra of Capo Palinuro (Salerno, Italy) during the last 26 years have been evaluated using growth forms and trophic guilds as non-taxonomic descriptors, informative of the structure and the functioning of the cave ecosystem, respectively. Photographic samples were collected in 1992 and 2018 to investigate the stability of the ecosystem response to the three main environmental gradients occurring inside the cave: i) confinement, ii) depth, and iii) light. Benthic communities were well spatially distributed along the three gradients inside the cave according to both the morphology and the feeding strategy of organisms, although the zonation was less marked considering trophic guilds. Gradients persisted and zones remained distinct through time, notwithstanding significant changes in community composition. The trophic organization was preserved throughout the cave, but significant changes in the spatial organization of benthic assemblages were widely observed, mainly due to 3-dimensional growth forms replaced by 2-dimensional (i.e., encrusting) growth forms and by increased sedimentation, thus causing the structural homogenization of the cave community. The outermost and the deepest sectors of the cave experienced higher changes compared to the most confined, blind-ended, sector and to the shallowest depths, which resulted comparatively more stable. From a functional point of view, filter feeders always dominated the communities (even considering their shift from erect to encrusting morphologies) and the few observed changes were due to the reduction of photophilic autotrophs and active ciliate without lophophore and the increase of mixotrophic sponges. As local human pressures remained low through the period considered, the changes observed are likely to be mainly due to global warming, which caused increased sea surface water temperatures and repeated summer heat waves (reported in 1994, 2003, 2008, 2012, and 2015). Regular monitoring programs on marine caves should be promoted to create historical series of data precious to better understand magnitude and pattern of change in the long-term evolution, and to estimate the recovery time of such priority habitats. • We investigated changes in the last 26 years in a submerged marine cave. • Three main environmental gradients were analysed: confinement, depth, and light. • Gradients persisted and zones remained distinct through time. • We observed significant changes in the spatial organization of benthic assemblages. • Changes were likely due to global warming and repeated summer heat waves. [ABSTRACT FROM AUTHOR]

Abstract Marine coastal ecosystems are facing structural and functional changes due to the increasing human footprint worldwide, and the assessment of their long-term changes becomes particularly challenging. Measures of change can be done by comparing the observed ecosystem status to a purposely defined reference condition. In this paper, a geospatial modelling approach based on 2D mapping and morphodynamic data was used to predict the natural position of the upper limit (i.e., the landward continuous front) of Posidonia oceanica seagrass meadows settled on soft bottom. This predictive model, formerly developed at the regional spatial scale, was here applied for the first time at the Mediterranean spatial scale in eight coastal areas of Spain, France, Italy, and Greece showing different coastal morphologies and hydrodynamic characteristics, and affected by a number of natural and/or human local disturbances. The model was effective in measuring the regression (i.e., seaward withdrawal) of the meadow upper limit. In all the meadows investigated the upper limit was regressed, laying deeper than the reference condition, with the proportion of regression ranging from 17.7% to 98.9%. The highest values of regression were found in Spain and in France, and were consistent with the highest levels of fragmentation detected with map analysis and of coastal pressures. This geospatial modelling approach represents an effective tool to define the reference conditions when proper pristine areas or historical data are not available, thus allowing the assessment of long-time changes experienced by seagrass ecosystems due to human impacts. Highlights • Reference conditions are needed to measure long-term change in marine ecosystems. • We modelled the upper (landward) limit of seagrass meadows at Mediterranean scale. • All meadow upper limits appeared regressed and fragmented due to local disturbances. • Modelling represents an effective tool for evaluating seagrass meadow conditions. [ABSTRACT FROM AUTHOR]

Sea-level changes have shaped the world's carbonate platform margins and continental shelves, leaving typical geomorphic imprints, such as drowned reef terraces. In this paper, we present the results of 112 scuba diving transects across seven different Maldivian atolls and one multibeam survey around Malé Island, the capital of Maldives. We report on the occurrence of drowned reef terraces down to 120 m depth. In total, we identified six levels of submerged terraces that we consider as indicative of periods of time with stable or slowly rising sea level that can be attributed either to deceleration of the last deglacial sea-level rise or to Late Quaternary sea-level highstands. We compare our dataset to the depth of reef terraces reported globally, and we discuss the reasons why common global submerged terrace levels are difficult to identify in the field record. [ABSTRACT FROM AUTHOR]

The epiphytes of seagrass leaves constitute a peculiar community, comprised of a number of species specialized for this living substrate. Several studies report on the response of epiphytes to different pressures but no information exists about the effects of summer heatwaves, which have become frequent events in the last decades. This paper represents the first attempt to investigate the change in the leaf epiphyte community of the Mediterranean seagrass Posidonia oceanica due to the heatwave occurred in summer 2003. Thanks to a series of data collected seasonally between 2002 and 2006, and punctual data in the summers of 2014 and 2019, we assessed the change over time in the leaf epiphyte community. Temperature data trends were analysed through linear regression, while multivariate analyses (i.e., nMDS and SIMPER) were applied to cover data in order to assess changes over time in the epiphyte community. As a whole, the two most abundant taxa were the crustose coralline alga Hydrolithon and the encrusting bryozoan Electra posidoniae , which displayed the highest average cover values in summer (around 19%) and spring (around 9%), respectively. Epiphytes proved to be sensitive to temperature highs, displaying different effects on cover, biomass, diversity and community composition. Cover and biomass exhibited a dramatic reduction (more than 60%) after the disturbance. In particular, Hydrolithon more than halved, while E. posidoniae dropped sevenfold during summer 2003. While the former recovered comparatively quickly, the latter, as well as the whole community composition, apparently required 16 years to return to a condition similar to that of 2002. • Seagrass leaf epiphytes constitute a specialized community. • Epiphytes of Posidonia oceanica have been impacted by summer heatwave in 2003. • Epiphytic cover and biomass exhibited a dramatic reduction. • Epiphyte community composition required 16 years to recover. [ABSTRACT FROM AUTHOR]

Marine caves are unique and vulnerable habitats exhibiting high biodiversity and heterogeneity, but threatened by multiple global and local disturbances. Marine caves, although widely distributed along the Mediterranean coast, suffer for the lack of quantitative data on their structure and function, which hinder their conservation status assessment. Thanks to the availability of a nearly 30-year-long series of data (1986–2013), we evaluated ecosystem change in the Bergeggi marine cave (Ligurian Sea, NW Mediterranean), a cave with a complex shape and high habitat heterogeneity. Non-taxonomic descriptors were adopted, namely growth forms (GF) and trophic guilds (TG), which are informative about ecosystem structure and functioning, respectively. The cave experienced a general trend of change during the last three decades, mainly due to the decline in the cover of sessile organisms (especially 3-dimensional forms) matched by an increase of turf and sediment, thus causing the structural and functional homogenization of the cave community. While change before 2004 had been attributed to climatic factors (especially to the summer heat waves of 1999 and 2003), the most important rate of change was observed between 2009 and 2013, coinciding with recent major beach nourishments and the extension of the neighbouring Vado Ligure harbour, thus providing evidences on the importance of local disturbances deriving from coastal interventions. Monitoring the status of cave ecosystems is urgently needed, and the use of effective indicators, such as the specific traits here adopted (morphology and feeding strategy), could provide effective tools to assist marine cave conservation. [ABSTRACT FROM AUTHOR]

Increasing anthropogenic pressure on coastal regions, coupled with a conflicting relationship between ecosystem health and economic growth, has resulted in a worldwide deterioration of marine ecosystems and loss of ecosystem services. The seagrass Posidonia oceanica is an emblematic example, constituting extensive and highly valuable meadows whose extent largely declined in the last decades. In this paper, more than one century of history of P. oceanica meadows has been reconstructed in a NW Mediterranean region combining models and historical information. The equivalent economic value of P. oceanica ecosystem functions was evaluated according to a donor-side approach and compared with the main economic sector of the region. A loss of more than 50% of the original surface of P. oceanica meadow extent has been documented between 1850 and around 1980, followed by stabilization in the last decades. Decline of P. oceanica has often been coupled with its replacement by the more tolerant seagrass species Cymodocea nodosa , only partially compensating for the loss of P. oceanica . The loss of the value of ecosystem functions between 1861 and 2009 was computed in 1106.8 billion emergy-euros (em€), a figure greater than the value added in the same period by tourism-related activities. Protection measures undertaken in the last decades slowed down the decline of P. oceanica meadows, while no concomitant decrease of the regional economic growth occurred. This study illustrates the tradeoffs between ecosystem conservation and economy growth, underlining the importance of long-term monitoring for environmental management and preservation of the natural capital. [ABSTRACT FROM AUTHOR]

Paracoryne huveiis a rare encrusting hydrozoan living in the intertidal zone of the North-western Mediterranean Sea, from the Catalan coast to the Ligurian Sea. In 2014, a large bloom ofP. huveiwas recorded along the cliffs of the Marine Protected Area ‘Isola di Bergeggi’ (Ligurian Sea). The species has shown densities related to important biomass values never previously recorded (wet weight as high as 1600 g m−2), creating a continuous belt up to 1 m wide from February to April. At an increasing distance from the promontory, the species decreased in abundance, assuming a spotted aspect comparable to the colonies recorded by earlier researchers. In the Bergeggi area, the species has exhibited an almost complete cover of the lower intertidal zone, and for the first time it was recorded in the infralittoral and upper intertidal zone and in tide pools, demonstrating a wider range of habitat than had previously been observed. The life cycle appeared significantly shorter than cycles reported in earlier literature, and this phenomenon has been compared with similar observations from other shallow water hydrozoans in the same area. The abundance of the species was continually monitored in 2015–2016 to help assess the inter-annual variations in relation to temperature and rainfall trends and, indirectly, to competition with other species. Finally, a comparison of the 59 years of scattered data of occurrence in the literature has shownP. huveito be a strict stenothermal species, reported only in winters characterized by average temperatures. [ABSTRACT FROM PUBLISHER]

Mapping marine coastal habitats provides an important aid to the long-term sustainability of urban development and the conservation of marine biodiversity. Historical maps, when available, may represent effective tools to evaluate quali-quantitative changes over time and to fix reference conditions. Scientific mapping of marine habitats is relatively recent, but the existence of fishery maps could compensate, after a critical evaluation, for the lack of more rigorous historical data. Coralligenous reefs are among the most important marine coastal habitats in the Mediterranean Sea, whose conservation requires, as a first step suggested by the recent European Directives, updated and detailed cartographies. This paper compares the recent cartographies (i.e. 2006 and 2009) on coralligenous reefs distribution in Liguria (NW Mediterranean Sea) with two historical fishery maps (i.e. dating back to the second half of the last century), on a GIS platform. Application of the Reliability Index (RI) showed that both historical sources can be trusted, with some caution. Fishery maps report few quantitative data (e.g. extent in hectares of coralligenous reefs) that are in little agreement with recent cartographies, mainly due to errors in positioning. In contrast, qualitative data (i.e. presence/absence in a specific site) represent the main information found in these maps and agree much more with the recent ones. It is more than likely that many of the rocky bottoms reported only in the fishery maps may host coralligenous reefs, which are apparently unknown in the recent cartographies. Latent information provided by this kind of historical maps may thus be useful for planning new surveys to sea-truthing on sites where no recent information is available and to promote the ecological studies required for their conservation. [ABSTRACT FROM AUTHOR]

A multidisciplinary approach was applied to investigate the role of abiotic constraints in the settlement of Posidonia oceanica on shallow rocks in two coastal areas of the Ligurian Sea (Italy, NW Mediterranean). Meadows developed very shallow upper limits, at 1.5 m depth in both areas, and with a distinctive morphology of stripes growing on rocky outcrops orthogonal to the coastline. Application of a predictive model to indicate the reference condition zone for the meadow upper limit, already validated on meadows developing on soft-bottoms, was not adequate for these rocky substrata as the meadow upper limits were found shallower than model predictions (>5 m depth). Geological and geomorphological characteristics of the rocky shores were analysed through geomechanic and petrographic analyses (i.e. thin sections, SEM analyses, rock hardness tests) whilst the shape and the features of the meadows (i.e. shoot density and maximum leaf length) were assessed through scuba diving surveys. Among the different lithotypes occurring at the sites in the alternating and interbedded outcrops, P. oceanica was passively selected (i.e. due to the seedlings survival and settlement there) on the strongest (i.e. less erodible) lithotypes, whilst the comparatively weaker and more erodible rocks remained unvegetated and covered by a layer of soft-sediments. P. oceanica , settling on specific rocky substrata with favourable lithological and geomechanical characteristics, is able to establish outside the theoretical reference zone predicted by the model for soft sediments due to greater attachment strength and possible resistance to hydrodynamic forces. Combining biological, ecological, mineralogical, geological and geomorphological approaches was effective for explaining the primary role of substratum nature in the spatial variability of seagrass meadows, with geomechanical and lithological characteristics of the rocks being equally important abiotic factors than sedimentological features. [ABSTRACT FROM AUTHOR]

Coral reefs are threatened by multiple global and local disturbances. The Maldives, already heavily hit by the 1998 mass bleaching event, are currently affected also by growing tourism and coastal development that may add to global impacts. Most of the studies investigating effects of local disturbances on coral reefs assessed the response of communities along a horizontal distance from the impact source. This study investigated the status of a Maldivian coral reef around an island where an international touristic airport has been recently (2009–2011) built, at different depths along the reef profile (5–20 m depth) and considering the change in the percentage of cover of five different non-taxonomic descriptors assessed through underwater visual surveys: hard corals, soft corals, other invertebrates, macroalgae and abiotic attributes. Eight reefs in areas not affected by any coastal development were used as controls and showed a reduction of hard coral cover and an increase of abiotic attributes (i.e. sand, rock, coral rubble) at the impacted reef. However, hard coral cover, the most widely used descriptor of coral reef health, was not sufficient on its own to detect subtle indirect effects that occurred down the reef profile. Selecting an array of descriptors and considering different depths, where corals may find a refuge from climate impacts, could guide the efforts of minimising local human pressures on coral reefs. [ABSTRACT FROM AUTHOR]

A new index of ecological status, named Mesophotic Assemblages Ecological Status (MAES) index, was elaborated on the basis of ROV (Remotely Operated Vehicle) photography and video footage in order to assess the status of mesophotic megabenthic assemblages from hard bottom. The index was tested on seven sites located between 50 and 150 m depth in the Ligurian and Tyrrhenian seas (western Mediterranean Sea). The MAES index considers three main parameters: (i) the community structure (number of megabenthic taxa, percent biotic cover in the basal layer, density of erect species); (ii) the condition of the dominant erect species (average height, percent of colonies with epibiosis/necrosis); (iii) the visible human impact (density of marine litter, including lost fishing gears). Two versions of the index have been elaborated, the complete version (MAES) and the quick version ( q -MAES), which showed comparable results, therefore suggesting the possibility of fastening assessment times. The sensitivity of the MAES index was correlated with the putative human pressure acting upon the site (semi-quantitatively assessed considering fishing effort and coastal urbanization). A standard working protocol related to the evaluation of the MAES index is here proposed with the intent to create an effective monitoring tool for the assessment of the ecological status of mesophotic assemblages on a large scale, as required by the EU Marine Strategy Framework Directive. MAES index will enhance the comprehension of the dynamics of mesophotic Mediterranean megabenthic assemblages with respect to human pressures and will also provide marine scientists and managers with a valuable tool specifically designed for the conservation of such vulnerable marine ecosystems. [ABSTRACT FROM AUTHOR]

Within the framework of the EU Life+ project named LIFE09 NAT/IT/000190 ARION, a permanent automated real-time passive acoustic monitoring system for the improvement of the conservation status of the transient and resident population of bottlenose dolphin (Tursiops truncatus) has been implemented and installed in the Portofino Marine Protected Area (MPA), Ligurian Sea. The system is able to detect the simultaneous presence of dolphins and boats in the area and to give their position in real time. This information is used to prevent collisions by diffusing warning messages to all the categories involved (tourists, professional fishermen and so on). The system consists of two gps-synchronized acoustic units, based on a particular type of marine buoy (elastic beacon), deployed about 1 km off the Portofino headland. Each one is equipped with a four-hydrophone array and an onboard acquisition system which can record the typical social communication whistles emitted by the dolphins and the sound emitted by boat engines. Signals are pre-filtered, digitized and then broadcast to the ground station via wi-fi. The raw data are elaborated to get the direction of the acoustic target to each unit, and hence the position of dolphins and boats in real time by triangulation. [ABSTRACT FROM AUTHOR]

The effects of global change are particularly serious in areas where range shifts of species are physically constrained such as the Ligurian Sea, which is one of the coldest sectors of the Mediterranean. In this basin, historical information on water temperature (from the sea surface down to 75 m depth) dates back to the 1950s. Early studies also recorded warm-water species occurrence. Thanks to these data we provide the first detailed characterization of water temperature variation from 1958 up to 2010 in the layer 0-75 m depth. We coupled this analysis with the available information on rocky reef epibenthic communities (literature review from 1955 to 1964 and field data from 1980 to 2010). The analysis of water temperature revealed several patterns of variation: a cooling phase from 1958 to 1980, a phase of rapid warming from 1980 to 1990 and a phase of slower warming from 1990 to 2010. Inter-annual variation in temperature increased over the entire period for the water layer down to 20 m. Warm-water native and alien species richness increased during the warming phases. Literature estimates suggest a decrease in warm-water native species richness during the cooling phase. The analysis of quantitative data collected in the early 1990s and late 2000s indicated a decrease in the cover of warm-water native species on shallow rocky reefs and an increase in deeper waters. We argue that increased inter-annual variation in water temperature may disadvantage native warm-water species in shallow waters. Our results indicate that the effect of temperature rises in cold, constrained basins may be more complex than the simple prediction of species changing their geographical range according to their thermal limits. [ABSTRACT FROM AUTHOR]

Marine ecosystems are subject to global and local impacts, both contributing to dramatic changes in coastal communities. Assessing such changes requires time series or the revisitation of sites first surveyed in the past. In both cases, data are not necessarily collected by the same observers, which could lead to a bias in the results. In the Marine Protected Area (MPA) of Capo Carbonara (Sardinia, Italy), established in 1998, rocky reef communities were first assessed in 2000 by two diving scientists. Twenty years later, the same rocky reefs were resurveyed using the same method by two other diving scientists. In both surveys, semi-quantitative data on conspicuous species were collected at five sites in four depth zones, providing the possibility of assessing change over time. To explore the influence of climate and local pressures, existing data on sea surface temperature, resident population, tourism and diving activities were analysed. The reef communities of the Capo Carbonara MPA have distinctly changed over time, mostly under the effect of seawater warming, as highlighted by the occurrence of thermophilic species and by other climate-related indicators. On the other side, species vulnerable to local human pressures have increased over time, demonstrating the effectiveness of the protection measures undertaken by the MPA. Comparing data collected by four different observers in the two periods demonstrated that change over time was significantly greater than variability between the observers. • Revisiting sites monitored in the past allows analysis of change over time. • Data are rarely collected by the same researcher, this may influence sampling quality. • Design of monitoring activities should consider the variability between observers. • A drastic change in reef communities of the Capo Carbonara MPA was observed. • Variability between observers did not hamper detecting change over time. [ABSTRACT FROM AUTHOR]

A theoretical model of structure and functioning was constructed for the Mediterranean undersea cave ecosystem. This model integrates almost all representative components of the cave ecosystem and gives an idea of their faunal compositions, characteristics and related interactions. This model constitutes the basis of the Ecosystem-Based Quality Index (EBQI) of the European Union's Marine Strategy Framework Directive, which aims at evaluating the ecological quality of an ecosystem. It is based on four crucial complementary elements: (i) each component was weighted in accordance with its importance in determining the structure and functioning of the cave ecosystem; (ii) a suite of relevant parameters were defined to assess the ecological state of each component of the cave ecosystem; (iii) these parameters were aggregated into one relevant index, the Cave EBQI (CavEBQI), to summarize the quality evaluation for each cave site; (iv) each value of ecological state is accompanied by a Confidence Index as a measure of its reliability. The CavEBQI was used on 22 Mediterranean undersea caves of France and Italy. Disparities of ecological quality were found among caves but most of them ranged from moderate to high ecological quality. For some caves, no conclusion can be drawn when our method predicts a poor reliability of the evaluation of their ecological quality. This ecosystem-based evaluation of the quality of undersea caves seems to be a powerful tool, with the advantage of being based on almost all its components, rather than just on a few species. It is accompanied by a measure of its reliability, hence it provides a reliable idea of the ecological state of the entire ecosystem at each cave site. Monitoring the ecological state of caves and the effects of disturbances over large geographic and temporal scales is made possible with CavEBQI. Applying the same method to other ecosystems, can provide an integrated view of a marine region, which is essential when addressing questions about protection, conservation and restoration. [ABSTRACT FROM AUTHOR]

Sustained functioning of ecosystems is predicted to depend upon the maintenance of their biodiversity, structure and integrity. The large consensus achieved in this regard, however, faces to the objective difficulty of finding appropriate metrics to measure ecosystem functioning. Here, we aim at evaluating functional consequence of the phase shift occurring in meadows of the Mediterranean seagrass Posidonia oceanica , a priority habitat that is undergoing regression in many coastal areas due to multiple human pressures. Structural degradation of the P. oceanica ecosystem, consequent to increasing coastal exploitation and climate change, may result in the progressive replacement of this seagrass by opportunistic macrophytes, either native or alien. Reviewing published information and our personal records, we measured changes in biological habitat provisioning, species richness and biomass associated to each of the alternative states characterizing the phase shift. Then, ecosystem functioning was assessed by computing the exergy associated to each state, exergy being a state variable that measures the ecosystem capacity to produce work. Phase shift was consistently shown to imply loss in habitat provision, species richness, and biomass; structural and compositional loss was parallelled by a reduction of exergy content, thus providing for the first time an objective and integrative measure of the loss of ecosystem functioning following the degradation of healthy seagrass meadows. [ABSTRACT FROM AUTHOR]

Understanding the effects of environmental change on ecosystems requires the identification of baselines that may act as reference conditions. However, the continuous change of these references challenges our ability to define the true natural status of ecosystems. The so-called sliding baseline syndrome can be overcome through the analysis of quantitative time series, which are, however, extremely rare. Here we show how combining historical quantitative data with descriptive ‘naturalistic’ information arranged in a chronological chain allows highlighting long-term trends and can be used to inform present conservation schemes. We analysed the long-term change of a coralligenous reef, a marine habitat endemic to the Mediterranean Sea. The coralligenous assemblages of Mesco Reef (Ligurian Sea, NW Mediterranean) have been studied, although discontinuously, since 1937 thus making available both detailed descriptive information and scanty quantitative data: while the former was useful to understand the natural history of the ecosystem, the analysis of the latter was of paramount importance to provide a formal measure of change over time. Epibenthic assemblages remained comparatively stable until the 1990s, when species replacement, invasion by alien algae, and biotic homogenisation occurred within few years, leading to a new and completely different ecosystem state. The shift experienced by the coralligenous assemblages of Mesco Reef was probably induced by a combination of seawater warming and local human pressures, the latter mainly resulting in increased water turbidity; in turn, cumulative stress may have favoured the establishment of alien species. This study showed that the combined analysis of quantitative and descriptive historical data represent a precious knowledge to understand ecosystem trends over time and provide help to identify baselines for ecological management. [ABSTRACT FROM AUTHOR]

Biodiversity is a portmanteau word to indicate the variety of life at all levels from genes to ecosystems, but it is often simplistically equated to species richness; the word ecodiversity has thus been coined to address habitat variety. Biodiversity represents the core of the natural capital, and as such needs to be quantified and followed over time. Marine Protected Areas (MPAs) are a major tool for biodiversity conservation at sea. Monitoring of both species and habitat diversity in MPAs is therefore mandatory and must include both inventory and periodic surveillance activities. In the case of inventories, the ideal would be to census all species and all habitats, but while the latter goal can be within reach, the former seems unattainable. Species inventory should be commeasured to investigation effort, while habitat inventory should be based on mapping. Both inventories may profit from suitability spatial modelling. Periodic surveillance actions should privilege conspicuous species and priority habitats. Efficient descriptor taxa and ecological indices are recommended to evaluate environmental status. While it seems obvious that surveillance activities should be carried out with regular recurrence, diachronic inventories and mapping are rarely carried out. Time series are of prime importance to detect marine ecosystem change even in the absence of direct human impacts. [ABSTRACT FROM AUTHOR]

Posidonia oceanica is an endemic Mediterranean seagrass used as a 'biological quality element' in monitoring programmes of the EU Water Framework Directive, providing information about coastal ecosystems status. The regression of P. oceanica meadows caused a growing interest among policy makers to assess the value of seagrasses and to increase their protection. An evaluation of P. oceanica meadows located in the Ligurian-Provençal basin (NW Mediterranean) through a biophysical approach is here developed. Six meadows located in Liguria (Italy) and Corsica (France) were investigated by applying the emergy analysis to assess the natural capital (NC) stocked by leaves and rhizomes components. Results highlighted the importance of carrying out an analysis of the variations in the NC value in both components: rhizomes defined the growth stage and the capacity to store NC over time; leaves provided information on the variability due to disturbances in the water column. Emergy analysis allows defining the NC, in terms of resources needed to maintain the meadows and to provide services to coastal communities. This research is inserted into the effort of incorporating the NC evaluation into marine planning and decision making to achieve nature conservation goals, while ensuring the sustainable exploitation of marine resources. [ABSTRACT FROM AUTHOR]

Seawater warming is impacting marine ecosystems, but proper evaluation of change requires the availability of long-term biological data series. Mesco Reef (Ligurian Sea, Italy) offers one of the longest Mediterranean data series on sessile epibenthic communities, based on underwater photographic surveys. Photographs taken in four stations between 20 m and 40 m depth allowed calculating the percent cover of conspicuous species in 1961, 1990, 1996, 2008, and 2017. Multivariate analysis evidenced an abrupt compositional change between 1990 and 1996. A parallel change was observed in Ligurian Sea temperatures. Two invasive macroalgae (Caulerpa cylindracea and Womersleyella setacea) became dominant after 1996. Community diversity was low in 1961 to 1996, rapidly increased between 1996 and 2008, and exhibited distinctly higher values in 2008–2017. A novel community emerged from the climate shift of the 1990s, with many once characteristic species lost, reduced complexity, biotic homogenization, greater diversity and domination by aliens. Only continued monitoring will help envisage the possibility for a reversal of the present phase shift or for further transformations driven by global change. [ABSTRACT FROM AUTHOR]