1,721,261 research outputs found
Component Mode Synthesis methods in a body in white noise and vibration analysis
No full textIn this work the Dynamic Substructuring (DS) approach has been applied to a noise, vibration and harshness (NVH) problem within the automotive engineering field. In particular, a NVH analysis has been carried out on the body in white of a passenger car. The work focuses on the theory of Component Mode Synthesis (CMS). Two CMS reduction methods, the Craig-Bampton and the Craig-Chang, have been applied to the body in white of the Volvo V40. The influence of some different parameters has been investigated. In particular, the effect of the reduction basis on the response accuracy and on the reduction time has been studied. Moreover, the effect of the connection property between different parts of the model has been examined. The simulation times of the reduced models and of the full Finite Element (FE) model have been compared. The results show us that the Craig-Chang method performs better when the modes are retained up to one and a half time the maximum frequen-cy response studied. Additionally, the Craig-Chang method gives a very accurate representation of the system dynamics even when connections with low stiffness are used. Finally, it is possible to reduce the simulation time up to 90% if CMS methods are used instead of the full FE model
Seabird influence on ecological processes in coastal marine ecosystems: An overlooked role? A critical review
No full textSeabirds are vital, but overlooked, components of coastal marine ecosystems and may connect the marine and terrestrial environment at a global scale, significantly contributing to inter-habitat connectivity and the provision of multiple ecosystem services. Although the ecological and functional role of birds in terrestrial areas, islands in particular, has been deeply studied since the last century, the same does not hold true for coastal marine areas. Given the importance of coastal areas for seabirds worldwide and, at the same time, the high vulnerability of both, looking into the role of seabirds in influencing the ecosystem functioning in coastal areas is needed nowadays. Here, we review the current knowledge regarding the role of seabirds on coastal ecological processes giving particular emphasis on the linkage between the seabird functions that are crucial in influencing the ecological processes and the provision of ecosystem services, and disservices, for the human well-being. Seabirds can contribute to shaping coastal ecological processes and services in a multitude of ways, among which directly influencing trophic status, environmental contamination, biodiversity and food webs through trophic (bottom-up or top-down) and non-trophic processes. We identified areas for future research to further clarify this linkage and promote seabird conservation
Preferential assimilation of seagrass detritus by two coexisting Mediterranean sea cucumbers: Holothuria polii and Holothuria tubulosa
No full textHolothuria polii and Holothuria tubulosa are two of the most commercially exploited sea cucumbers of the Mediterranean Sea. As deposit-feeders, they represent an important component of the benthic community. Hence, knowledge of their feeding behaviour is crucial for understanding their function in terms of benthic ecology and sediment dynamics. Using information obtained from stable isotope analysis, the food selectivity/assimilation, temporal variations in diet and trophic niche of H. polii and H. tubulosa were investigated. Analysis of carbon and nitrogen isotopic ratios in body wall tissue showed a preferential assimilation of seagrass detritus among multiple food sources, with a total contribution to the diet ranging from 63% to 74%. The temporal changes in δ13C and δ15N values followed the seagrass isotopic dynamics with depleted values in winter and enriched values in summer. Additionally, δ13C and δ15N measurements were used to outline the species' trophic niche width. The two species coexist, showing an overlap on the δ13C axis and a partial degree of niche segregation on the δ15N axis. Our results provide an overview on the feeding activity of H. polii and H. tubulosa, providing evidence of their crucial role on the seagrass detrital pathways for Mediterranean coastal ecosystems
A tight interaction between the native seagrass Cymodocea nodosa and the exotic Halophila stipulacea in the Aegean Sea highlights seagrass holobiont variations.
Full text linkSeagrasses harbour bacterial communities with which they constitute a functional unit called holobiont that responds as a whole to environmental changes. Epiphytic bacterial communities rapidly respond to both biotic and abiotic factors, potentially contributing to the host fitness. The Lessepsian migrant Halophila stipulacea has a high phenotypical plasticity and harbours a highly diverse epiphytic bacterial community, which could support its invasiveness in the Mediterranean Sea. The current study aimed to evaluate the Halophila/Cymodocea competition in the Aegean Sea by analysing each of the two seagrasses in a zone where these intermingled, as well as in their monospecific zones, at two depths. Differences in holobionts were evaluated using seagrass descriptors (morphometric, biochemical, elemental, and isotopic composition) to assess host changes, and 16S rRNA gene to identify bacterial community structure and composition. An Indicator Species Index was used to identify bacteria significantly associated with each host. In mixed meadows, native C. nodosa was shown to be affected by the presence of exotic H. stipulacea, in terms of both plant descriptors and bacterial communities, while H. stipulacea remained almost unchanged. This study provided evidence of the competitive advantage of H. stipulacea on C. nodosa in the Aegean Sea and suggests the possible use of associated bacterial communities as a descriptor of native seagrass sustainability
Habitat use and isotopic niche variability during ontogeny of the gilthead seabream Sparus aurata within a coastal lagoon
No full textThe gilthead seabream Sparus aurata is known to enter coastal lagoons and estuaries during the first stages of post-larval and juvenile development. The high habitat heterogeneity and shallowness that characterize such ecosystems offer plentiful food and shelter for this species that hence undergoes rapid growth. The juvenile stage development occurs through stepwise changes in anatomy, physiology, and behavior that is linked strongly to ontogenetic changes in habitat and resource use. We used carbon and nitrogen stable isotopes to assess: (1) the role of different habitats in supporting the trophic pathway leading to S. aurata over early stages of development within a coastal lagoon, (2) ontogenetic diet shifts and how they reflect in changes of the trophic niche of the species.
Fish and organic matter sources were sampled in spring and summer 2014 and 2015, in different sites of the Venice lagoon representing salt marsh and seagrass meadow habitats located along a confinement gradient. Bayesian mixing models, standard ellipse areas and community-wide metrics were applied to the four size classes detected, according to standard length (SL): post-larvae, SL<20 mm, juveniles I 20<SL<40 mm, juveniles II, 40<SL<60 mm and sub-adults SL>60 mm. Organic matter sources considered were plankton, particulate and sedimentary organic matter (POM and SOM), seagrasses and macroalgae.
We observed a clear shift in source contribution through size classes, with slight differences among habitats. The greatest contribution to the trophic pathway of S. aurata shifted from a mix of POM, SOM and plankton for the post-larval stage, when the fish is only able to prey on very low trophic levels, to mainly seagrasses for the middle stages, to a mix of macroalgae and seagrasses for the sub-adults, characterised also by a high trophic plasticity. Additionally, the shift manifest in the isotopic niche, which varied in shape, width and position across size classes, with the main differences occurring between post-larvae and juveniles/sub-adults, in accordance to their diet shift that goes respectively from zooplanctivorous to zoobenthivorous habits. This study emphasises the important trophic role that coastal lagoon habitats provide to the early stages of S. aurata life cycle and links it to the implications that may result in terms of coastal management
Microbial Biofilms Along a Geochemical Gradient at the Shallow-Water Hydrothermal System of Vulcano Island, Mediterranean Sea
Full text linkShallow water hydrothermal vents represent highly dynamic environments where strong geochemical gradients can shape microbial communities. Recently, these systems are being widely used for investigating the effects of ocean acidification on biota as vent emissions can release high CO2 concentrations causing local pH reduction. However, other gas species, as well as trace elements and metals, are often released in association with CO2 and can potentially act as confounding factors. In this study, we evaluated the composition, diversity and inferred functional profiles of microbial biofilms in Levante Bay (Vulcano Island, Italy, Mediterranean Sea), a well-studied shallow-water hydrothermal vent system. We analyzed 16S rRNA transcripts from biofilms exposed to different intensity of hydrothermal activity, following a redox and pH gradient across the bay. We found that elevated CO2 concentrations causing low pH can affect the response of bacterial groups and taxa by either increasing or decreasing their relative abundance. H2S proved to be a highly selective factor shaping the composition and affecting the diversity of the community by selecting for sulfide-dependent, chemolithoautotrophic bacteria. The analysis of the 16S rRNA transcripts, along with the inferred functional profile of the communities, revealed a strong influence of H2S in the southern portion of the study area, and temporal succession affected the inferred abundance of genes for key metabolic pathways. Our results revealed that the composition of the microbial assemblages vary at very small spatial scales, mirroring the highly variable geochemical signature of vent emissions and cautioning for the use of these environments as models to investigate the effects of ocean acidification on microbial diversity
Aquaculture of emerging species in North-Eastern Atlantic and Mediterranean Sea: a systematic review on sea cucumber farming and potential development
Full text linkSea cucumbers are considered a traditional food delicacy in Asian countries. In last decades high market demand, uncontrolled exploitation and inadequate management have led to stock overexploitation, driving commercial interest in new target species and new areas. In recent years, Mediterranean and North-East Atlantic sea cucumbers have become fishing targets, and, due to overfishing, a significant decline of wild populations have been observed, with detrimental effects on benthic communities and ecosystems. Indeed, in addition to being an important economic resource, sea cucumbers play a key ecological role in benthic dynamics where they are involved as ecosystem engineers in the processing of organic matter in the detrital food web pathway. In this context, aquaculture can play a crucial role in supporting the conservation of natural stocks by reducing harvesting pressure on wild populations and enabling restoration programmes for depleted stocks. Commercial sea cucumber farming is already an established reality in the Indo-Pacific region, where it has become one of the most profitable sectors of aquaculture production. In Europe, on the other hand, sea cucumber aquaculture is still an emerging sector, whose development is hampered by poor and fragmented information on the farming requirements of native species. In this context, this systematic review was carried out with the aim of providing a comprehensive summary of the state of the art of farming practices of the European sea cucumbers considered as a target of commercial fisheries. A total of 34 original articles were included in this review, after title, abstract and full-text screening. The results highlighted a sharp increase in the number of studies over the last six years. Portugal, Turkey and Italy are the countries where most research has been carried out. Among the selected species, Holothuria tubulosa was the most studied, while only one article was found on Parastichopus regalis. The main aims of this review were i) to gather all available literature on the farming practices of North-East Atlantic and Mediterranean sea cucumber species, ii) to outline the most common farming practices, iii) to identify gaps and future directions in this emerging aquaculture sector
δ15N in deployed macroalgae as a tool to monitor nutrient input driven by tourism activities in Mediterranean islands
Full text linkMediterranean Sea is among the world's leading tourist destinations; however, the sharp increase in tourists during the high season may affect coastal seawater. The main aim of this study was to evaluate the occurrence and temporal variation of anthropogenic nutrients in coastal seawater in relation to tourist flows in three Mediterranean islands (Cyprus, Sicily and Rhodes), through short-term macroalgae deployments, coupled with δ15N analysis and GIS mapping. In all islands, an overall increase in macroalgae δ15N occurred over the deployment carried out in August in the tourist sites, suggesting the presence of anthropogenic nutrients. Decreasing δ15N values occurred at increasing distance from the coastline in two out of the three islands (Cyprus and Sicily). This study revealed the usefulness of the approach used in the assessment of tourism impact in terms of trophic enrichment and its potential to support competent authorities for the development of sustainable coastal management plans
The Atlantic blue crab Callinectes sapidus spreading in the Tyrrhenian sea: evidence of an established population in the Stagnone di Marsala (Sicily, southern Italy)
Full text linkThe blue crab Callinectes sapidus is a portunid brachyuran native of the Atlantic coasts of America. In the last decades, the species has greatly expanded its range in invaded areas, currently including the Atlantic coasts of Morocco, the Mediterranean Sea, the Black Sea as well as the eastern Atlantic coasts of Europe from Portugal to France, Belgium, and Germany. In the present study, several specimens of C. sapidus were collected in May, June and July 2021 in the Stagnone di Marsala, a semi-enclosed basin located in the north-western coast of Sicily (southern Italy, Mediterranean Sea) characterized by low hydrodynamics and water exchange with the adjacent open sea and high salinity conditions. Juveniles at diff erent instar stages and ovigerous females were repeatedly captured, suggesting the presence of an established population of the blue crab, despite the peculiar environmental conditions characterizing the basin. These fi ndings are discussed in the context of the current expansion of the species along the African coasts of the Mediterranean Sea
Environmental effects of tourism and its seasonality on Mediterranean islands: the contribution of the Interreg MED BLUEISLANDS project to build up an approach towards sustainable tourism
Full text linkThe Mediterranean basin is amongst the world’s main tourist destination, and its islands are a major attraction, being sites of historical, cultural and naturalistic importance. This is beneficial for the local economies, but it may also represent a great burden on the coastal environment, where other human pressures are concentrated. The awareness of detrimental side effects of tourism together with the importance to take into account social and economic facets has led to the concept of sustainable tourism, which, however, represents a goal far from being attained. A good opportunity to promote sustainable tourism was provided by the Interreg MED BLUEISLANDS project, whose main aim was to identify, address and mitigate the effects of the seasonal variation of waste generated by tourism on Mediterranean islands. Here, we present the methodological framework of the project aimed at biomonitoring coastal seawater in highly touristic sites using macroalgae as valuable bioindicators of seawater quality and improving its status through the implementation and assessment of mitigation measures that included also the involvement of stakeholders. Outcomes of the project highlighted the effectiveness of such an integrated approach, confirming the importance of choosing proper indicators and tools that can support the development of management plans aiming to mitigate environmental impact and foster sustainable tourism
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