Evidence of Transient Energy and Enstrophy Cascades in Tidal Flows: A Scale to Scale Analysis

Tidal currents are predominant in coastal areas, causing the generation of vortices at different scales. We reproduce the main process of vortex shedding generated in tidal systems with inlets and channels using a laboratory large-scale model. A filter-space technique is implemented to analyze nonlinear energy/ enstrophy transfer rates and map out the energy pathways through the flow scales of the measured velocity fields. We provide sound evidence of the transitional character of the energy cascades during a tidal period. The periodic generation and destruction of tidal vortices plays a relevant role in the transition from an inverse to a direct energy cascade within a tidal period. The period-averaged energy budget shows the coexistence of multiple cascades. Small scales follow a direct energy cascade, whereas a split-energy cascade is found at intermediate and large scales, where part of the injected energy goes to small scales and part to a larger flow scale

A New and aberrant species of <i>Dugesia</i> (Platyhelminthes, Tricladida, Dugesiidae) from Madagascar

In this paper we report a new species of Dugesia of the family Dugesiidae from Madagascar, representing the fourth species of freshwater planarian known from this global biodiversity hotspot. In some respects the new species is aberrant, when compared with its congeners, being characterized by a head with smoothly rounded auricles, a peculiar course of the oviducts, including the presence of a common posterior extension, and by the asymmetrical openings of the vasa deferentia at about halfway along the seminal vesicle. Further, it is characterized by a ventral course of the ejaculatory duct with a terminal opening, very long spermiducal vesicles and unstalked cocoons. Its diploid chromosome complement with 18 chromosomes represents an uncommon feature among fissiparous species of Dugesia

Dispersion processes in weakly dissipative tidal channels

We report the results of an extensive experimental campaign dedicated to the analysis of turbulent dispersion owing to the circulations in tidal environments, characterized by a tidal inlet and a channel with lateral tidal flats. We focus on weakly-convergent and weakly-dissipative estuaries or tidal embankments, where the internal waters communicate with the open sea through an inlet mouth. Tides are reproduced as single or multiple harmonics waves. Particle Image Velocimetry is employed to measure two-dimensional surface velocity fields. Large-scale macro-vortices, generated by vortex shedding during the flood phase from the inlet barrier, tend to occupy the entire tidal flats width and are completely flushed out during the ebb phase. In all experiments, an intense residual current, with shape influenced by the large-scale flood vortices, is observed. The presence of large-scale vortices and of a residual current strongly influences the Lagrangian auto-correlation functions and the corresponding absolute dispersion time evolution. Looping auto-correlations are the signature of both periodic forcing and vortices, ultimately, leading to super diffusive regimes. An asymptotic Brownian regime is always found for the investigated range of parameters allowing for an estimate of the horizontal dispersion coefficients which turn out to decrease with the friction parameter and tend to be enhanced when the semi-diurnal constituents prevail. Finally, multiple particle statistics show multiple regimes depending on particle separations, compared to a typical injection length scale that seems to coincide with the inlet mouth dimension

Sea waves transport of inertial micro-plastics: Mathematical model and applications

Plastic pollution in seas and oceans has recently been recognized as one of the most impacting threats for the environment, and the increasing number of scientific studies proves that this is an issue of primary concern. Being able to predict plastic paths and concentrations within the sea is therefore fundamental to properly face this challenge. In the present work, we evaluated the effects of sea waves on inertial micro-plastics dynamics. We hypothesized a stationary input number of particles in a given control volume below the sea surface, solving their trajectories and distributions under a second-order regular wave. We developed an exhaustive group of datasets, spanning the most plausible values for particles densities and diameters and wave characteristics, with a specific focus on the Mediterranean Sea. Results show how the particles inertia significantly affects the total transport of such debris by waves

Settling velocity of microplastics exposed to wave action

Microplastic (MP) debris is recognized to be one of the most serious threats to marine environments. They are found in all seas and oceanic basins worldwide, even in the most remote areas. This is further proof that the transport of MPs is very efficient. In the present study, we focus our attention on MPs’ transport owing to the Stokes drift generated by sea waves. Recent studies have shown that the interaction between heavy particles and Stokes drift leads to unexpected phenomena mostly related to inertial effects. We perform a series of laboratory experiments with the aim to directly measure MPs’ trajectories under different wave conditions. The main objective is to quantify the inertial effect and, ultimately, suggest a new analytical formulation for the net settling velocity. The latter formula might be implemented in a larger scale transport model in order to account for inertial effects in a simplified approach

Influence of initial conditions on absolute and relative dispersion in semi-enclosed basins

Absolute and relative dispersion are fundamental quantities employed in order to assess the mixing strength of a basin. There exists a time scale called Lagrangian Integral Scale associated to absolute dispersion that highlights the occurrence of the transition from a quadratic dependence on time to a linear dependence on time. Such a time scale is commonly adopted as an indicator of the duration needed to lose the influence of the initial conditions. This work aims to show that in a semi-enclosed basin the choice of the formulation in order to calculate the absolute dispersion can lead to different results. Moreover, the influence of initial conditions can persist beyond the Lagrangian Integral Scale. Such an influence can be appreciated by evaluating absolute and relative dispersion recursively by changing the initial conditions. Furthermore, finite-size Lyapunov exponents characterize the different regimes of the basin

Fluidics of Single and Double Blade Guillotine Vitrectomy Probes in Balanced Salt Solution and Artificial Vitreous

urpose: To assess the fluidics of double-vitreous cutter blade (DB) compared with single-blade (SB) guillotine with 23-, 25-, and 27-gauge vitrectomy probes. To assess flow characteristics and flow rates in viscous and viscoelastic fluids. Methods: We used Particle Image Velocimetry to measure the flow field close to the tip of each cutter probe and we derived kinematic quantities of interest, such as kinetic energy and acceleration. We performed measurements both on a balanced salt solution (BSS) and on a viscoelastic artificial vitreous (AV). Results: The flow rate is significantly higher with DB than SB vitrectomy probes, for a given pumping pressure and cutting rate. The fluid flow observed is very different between BSS and AV tests. Conclusions: The DB has more efficient fluidics than SB vitrectomy probe in all tested conditions. Fluid acceleration depends on the cutting frequency, especially in the case of measurements in AV. The flow rate strongly depends on the pressure and it is little affected by the cutting frequency, in a range of clinical interest. The 27-G DB produces flow rates similar to the 23- and 25-G SB, with significantly smaller acceleration. The flow induced in the AV is different from that in BSS and oscillates at different frequencies. Translational Relevance: DB cutters prove to be more efficient in terms of lower acceleration for a given flow rate. The latter is mainly controlled by aspiration pressure and less by cut rates. The influence of vitreous rheology deserves further investigations

Three-Dimensional Modelling of the Terra Nova Bay Sea Floor (Ross Sea - Antarctica)

The importance of gathering data on the Antarctic coastline and its adjacent waters has been widely recognised by the Antarctic Treaty Consultative Meeting (ATCM), the Council of Managers of National Antarctic Programs (COMNAP) and the Scientific Committee on Antarctic Research (SCAR). In particular, both for navigational safety and environmental monitoring, it is very desirable to increase hydrographic activity in those areas which have the most significant importance from a scientific or navigational point of view - such as in the continental shelf and continental slope areas of the western part of the Ross Sea. Quite apart from the safety of navigation requirements, knowledge of the seabed topography is necessary to study and understand the various phenomena taking place in the marine environment. For example, the movement of water masses and their mixing processes depend on the shape of the seabed and adjacent coastline. The sea area surrounding Antarctica is one of the least explored parts of the world’s oceans and the available bathymetric data is only sufficient to allow a very general analysis to be made. With the probable growth of tourism and fishing around Antarctica and with the increasing need to understand the effects on the world’s climate of Antarctic water patterns, it is necessary to consider powerful new techniques - such as threedimensional modelling of the sea floors - in order to build up more quickly an effective and reliable bathymetric data base of Antarctic waters

The stenoendemic cave-dwelling planarians (Platyhelminthes, Tricladida) of the Italian Alps and Apennines: Conservation issues

Despite being a fundamental component of biodiversity, several highly diverse taxa of aquatic invertebrates are still poorly known and poorly considered in protection programs. This is the case especially of several invertebrate species that inhabit groundwater. In this environment, invertebrates play significant roles in ecosystem services closely connected to the usefulness of these systems for human welfare and survival. The groundwater biodiversity of continental Italy is largely unknown and its importance is neglected in national and regional legislation. One of the most poorly studied groups of Italian groundwater fauna are planarians (Platyhelminthes, Tricladida). Most known species are endemic to small, single karst areas or a single cave, their geographic range never having been investigated in detail after the original description. The aims of this study are i) to provide the first conservation assessment of cave-dwelling planarians in the Italian Alps and Apennines, whose status is at present Not Evaluated in IUCN categories and ii) to evaluate which environmental constraints, including potential threats, possibly affect the occurrence of the species within different cave systems. Our results suggest that most of the cave-dwelling planarian species of continental Italy are threatened by water pollution and habitat destruction/alteration; moreover, datasets underline that there is a considerable conservation issue concerning stenoendemic planarians that may involve other cave-dwelling invertebrates with narrow geographic ranges. Generally, the underground habitat of most surveyed species appears to be deeply compromised and changed since the first species description

Sponges architecture by colour: new insights into the fibres morphogenesis, skeletal spatial layout and morpho-anatomical traits of a marine horny sponge species (Porifera)

This paper focuses on the skeletal architecture and morphotraits of the Mediterranean horny sponge Sarcotragus spinosulus (Demospongiae, Keratosa, Dictyoceratida, Irciniidae). This special endoskeletal system consists of a dense, variably complex connective architecture, which extends throughout the entire sponge body and is embedded in an abundant jelly-like extracellular matrix (ECM). To investigate the topographic arrangement and micro-morphotraits of these connective structures in detail and by colour, also during morphogenetic processes, histology techniques using light microscopy are essential. New information is provided on the coordinated morphogenetic processes that characterize the growth and assembly of collagenic prototype structures in the matrix of fibrous skeletal elements and drive skeleton remodelling. Our results also highlight some novelties and some remarkable peculiarities of fibrous, filamentous and fibrillar components at the levels of both composition and structure. The morphofunctional significance of skeletal architecture is suggested in the background of the anatomical complexity of S. spinosulus