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J. Mar. Sci. Eng., Volume 9, Issue 4 (April 2021) – 99 articles

Cover Story (view full-size image): This paper focuses on the state of the art of the Autonomous Observing Systems (AOS) used in Vessels of Opportunity (VOO) for collecting in situ atmospheric, oceanic and biogeochemical data. VOO can be military, research, cruise liners, fishing, ferries, or even private yachts or sailing boats. The use of AOS in these vessels can provide the opportunity for highly refined oceanographic data and improved derived data estimation, for local-, regional- or global-scale studies. An overall review of the systems implemented is presented. The present and future capabilities of VOO for measuring oceanic variables within the Portuguese context are described. View this paper
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Article
A Novel Hybrid Fuel Consumption Prediction Model for Ocean-Going Container Ships Based on Sensor Data
J. Mar. Sci. Eng. 2021, 9(4), 449; https://doi.org/10.3390/jmse9040449 - 20 Apr 2021
Viewed by 721
Abstract
Accurate, reliable, and real-time prediction of ship fuel consumption is the basis and premise of the development of fuel optimization; however, ship fuel consumption data mainly come from noon reports, and many current modeling methods have been based on a single model; therefore [...] Read more.
Accurate, reliable, and real-time prediction of ship fuel consumption is the basis and premise of the development of fuel optimization; however, ship fuel consumption data mainly come from noon reports, and many current modeling methods have been based on a single model; therefore they have low accuracy and robustness. In this study, we propose a novel hybrid fuel consumption prediction model based on sensor data collected from an ocean-going container ship. First, a data processing method is proposed to clean the collected data. Secondly, the Bayesian optimization method of hyperparameters is used to reasonably set the hyperparameter values of the model. Finally, a hybrid fuel consumption prediction model is established by integrating extremely randomized tree (ET), random forest (RF), Xgboost (XGB) and multiple linear regression (MLR) methods. The experimental results show that data cleaning, the size of the dataset, marine environmental factors, and hyperparameter optimization can all affect the accuracy of the model, and the proposed hybrid model provides better predictive performance (higher accuracy) and greater robustness (smaller standard deviation) as compared with a single model. The proposed hybrid model should play a significant role in ship fuel consumption real-time monitoring, fault diagnosis, energy saving and emission reduction, etc. Full article
(This article belongs to the Section Ocean Engineering)
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Article
Two-Channel System Dynamics of the Outer Weser Estuary—A Modeling Study
J. Mar. Sci. Eng. 2021, 9(4), 448; https://doi.org/10.3390/jmse9040448 - 20 Apr 2021
Viewed by 634
Abstract
In this paper, we unravel the mechanisms responsible for the development of the two-channel system in the Outer Weser Estuary. A process-based morphodynamic model is built based on a flat-bed approach using simplified boundary conditions and accelerated morphological development. The results are analyzed [...] Read more.
In this paper, we unravel the mechanisms responsible for the development of the two-channel system in the Outer Weser Estuary. A process-based morphodynamic model is built based on a flat-bed approach using simplified boundary conditions and accelerated morphological development. The results are analyzed in two steps: first, by checking for morphodynamic equilibrium in the simulations and second, by applying a newly developed method that interprets simulations based on categorization of the two-channel system and cross-sectional correlation analysis. All simulations reach a morphodynamic equilibrium and develop two channels that vary considerably over time and between the simulations. Variations can be found in the location and depth of the two channels, the development of the dominant channel over time and the alteration in the dominance pattern. The conclusions are that the development of the two-channel system is mainly caused by the tides and the basin geometry. Furthermore, it is shown that the alternation pattern and period are dependent on the dominance of the tides compared to the influence of river discharge. Full article
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Article
State-of-the-Art Methods to Improve Energy Efficiency of Ships
J. Mar. Sci. Eng. 2021, 9(4), 447; https://doi.org/10.3390/jmse9040447 - 20 Apr 2021
Cited by 2 | Viewed by 773
Abstract
Generating energy efficiency through behavioural change requires not only understanding and empathy with user interests and needs but also the fostering of energy saving awareness, a technique and framework that supports operators and ship owners. There is strong potential to make use of [...] Read more.
Generating energy efficiency through behavioural change requires not only understanding and empathy with user interests and needs but also the fostering of energy saving awareness, a technique and framework that supports operators and ship owners. There is strong potential to make use of different technical solutions to increase energy efficiency, but many cost-efficient solutions relate to carrot-and-stick incentives for operators to minimise energy consumption. These incentives range from voyage planning with weather routing eco-driving bonus, to torque limitations and changes in company policies, all of which demonstrate that the operators’ on-board importance for the energy consumption has been identified. Data collection will allow operators to make better decisions in the lifecycle of the ship from knowledge-driven design to operation, redesign and lifetime extension. Various systems are available for data acquisition, storage and analysis, some of which are delivered by well-known marine suppliers while others are stand-alone systems. The lack of standardization for data capture, transmission and analysis is a challenge, so systematic improvement is required in shipping companies to achieve energy savings. When these are achieved, they will be the result of customer requirements, cost pressure or individual driving forces in the companies. The potential energy savings, brought up in interviews, shows up to 35% on specific routes and up to 60% in specific maneuvers. These savings will be made feasible by operators and crews being involved in the decision-making process. Full article
(This article belongs to the Special Issue Performance Assessment of Ship Energy Efficiency)
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Article
Cavitating Flow in the Volute of a Centrifugal Pump at Flow Rates Above the Optimal Condition
J. Mar. Sci. Eng. 2021, 9(4), 446; https://doi.org/10.3390/jmse9040446 - 20 Apr 2021
Viewed by 540
Abstract
Cavitation is regarded as a considerable factor causing performance deterioration of pumps under off-design conditions, especially at overload conditions. To investigate the unsteady cavitation evolution around the tongue of a pump volute, and its influence on the flow field within passages of the [...] Read more.
Cavitation is regarded as a considerable factor causing performance deterioration of pumps under off-design conditions, especially at overload conditions. To investigate the unsteady cavitation evolution around the tongue of a pump volute, and its influence on the flow field within passages of the impeller, numerical calculations and several hydraulic tests were performed on a typical centrifugal pump with a shrouded impeller. Emphasis was laid on the cavitation evolution and blade-loading distribution at flow rates above the optimal value. Results indicated that vapor is likely to first emerge from the tongue of the volute rather than at the leading edge of the blades at overload conditions. In contrast to the designed condition, the flow distribution in each passage is obviously different. The flow rate of the passage reaches a maximum just past the location of the tongue, while the minimum flow rate value is projected to appear at the passage upstream. The cavitation at the tongue squeezes the flow area at the outlet of the corresponding flow passage of the tongue, thereby causing a huge growth in the flow rate at the impeller outlet. Full article
(This article belongs to the Section Ocean Engineering)
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Review
An Overview of the Sorption Studies of Contaminants on Poly(Ethylene Terephthalate) Microplastics in the Marine Environment
J. Mar. Sci. Eng. 2021, 9(4), 445; https://doi.org/10.3390/jmse9040445 - 19 Apr 2021
Cited by 5 | Viewed by 1043
Abstract
Marine pollution is one of the biggest environmental problems, mainly due to single-use or disposable plastic waste fragmenting into microplastics (MPs) and nanoplastics (NPs) and entering oceans from the coasts together with human-made MPs. A rapidly growing worry concerning environmental and human safety [...] Read more.
Marine pollution is one of the biggest environmental problems, mainly due to single-use or disposable plastic waste fragmenting into microplastics (MPs) and nanoplastics (NPs) and entering oceans from the coasts together with human-made MPs. A rapidly growing worry concerning environmental and human safety has stimulated research interest in the potential risks induced by the chemicals associated with MPs/NPs. In this framework, the present review analyzes the recent advances in adsorption and desorption studies of different contaminants species, both organic and metallic, on MPs made of Poly(Ethylene terephthalate). The choice of PET is motivated by its great diffusion among plastic items and, unfortunately, also in marine plastic pollution. Due to the ubiquitous presence of PET MPS/NPs, the interest in its role as a vector of contaminants has abruptly increased in the last three years, as demonstrated by the very high number of recent papers on sorption studies in different environments. The present review relies on a chemical engineering approach aimed at providing a deeper overview of both the sorption mechanisms of organic and metal contaminants to PET MPs/NPs and the most used adsorption kinetic models to predict the mass transfer process from the liquid phase to the solid adsorbent. Full article
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Article
Severity Scoring of Behavioral Responses of Sperm Whales (Physeter macrocephalus) to Novel Continuous versus Conventional Pulsed Active Sonar
J. Mar. Sci. Eng. 2021, 9(4), 444; https://doi.org/10.3390/jmse9040444 - 19 Apr 2021
Cited by 2 | Viewed by 1223
Abstract
Controlled exposure experiments (CEEs) have demonstrated that naval pulsed active sonar (PAS) can induce costly behavioral responses in cetaceans similar to antipredator responses. New generation continuous active sonars (CAS) emit lower amplitude levels but more continuous signals. We conducted CEEs with PAS, CAS [...] Read more.
Controlled exposure experiments (CEEs) have demonstrated that naval pulsed active sonar (PAS) can induce costly behavioral responses in cetaceans similar to antipredator responses. New generation continuous active sonars (CAS) emit lower amplitude levels but more continuous signals. We conducted CEEs with PAS, CAS and no-sonar control on free-ranging sperm whales in Norway. Two panels blind to experimental conditions concurrently inspected acoustic-and-movement-tag data and visual observations of tagged whales and used an established severity scale (0–9) to assign scores to putative responses. Only half of the exposures elicited a response, indicating overall low responsiveness in sperm whales. Responding whales (10 of 12) showed more, and more severe responses to sonar compared to no-sonar. Moreover, the probability of response increased when whales were previously exposed to presence of predatory and/or competing killer or long-finned pilot whales. Various behavioral change types occurred over a broad range of severities (1–6) during CAS and PAS. When combining all behavioral types, the proportion of responses to CAS was significantly higher than no-sonar but not different from PAS. Responses potentially impacting vital rates i.e., with severity ≥4, were initiated at received cumulative sound exposure levels (dB re 1 μPa2 s) of 137–177 during CAS and 143–181 during PAS. Full article
(This article belongs to the Special Issue Ocean Noise: From Science to Management)
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Article
Response of Benthic Diatom Assemblages to Contamination by Metals in a Marine Environment
J. Mar. Sci. Eng. 2021, 9(4), 443; https://doi.org/10.3390/jmse9040443 - 19 Apr 2021
Viewed by 618
Abstract
Studies on marine benthic diatoms in environments contaminated by metals are scarce. The typical structure of benthic diatom assemblages (species richness, diversity, dominance, dominant taxa) from undisturbed environments may be used as reference for contrasting with contaminated environments in order to observe how [...] Read more.
Studies on marine benthic diatoms in environments contaminated by metals are scarce. The typical structure of benthic diatom assemblages (species richness, diversity, dominance, dominant taxa) from undisturbed environments may be used as reference for contrasting with contaminated environments in order to observe how said assemblages respond to such disturbance. Thus, the Ho that the structure of benthic diatom associations and morphology of their frustules under contamination by metals would be normal, as in unpolluted environments was tested. To do this, concentrations of 24 metals were surveyed in a coastal zone impacted by mining residues, and the structure of benthic local diatom assemblages was described. Metal concentrations measurements for 15 metals surpassed the normal values of the upper earth cortex, seven were under the low range effect, and three (Cd, Cu, Zn) surpassed the medium range effect values. At a control site no element concentration was above the reference values for low range effect (LRE) or medium range effect (MRE) standards. There, diatom species richness (S) was high, particularly on seaweeds; where, 397 diatom taxa were recorded. In contrast, at the contaminated area 217 diatom taxa were recorded, but diversity (H’) ranged from 2.4 to 4.3. Relative high frequencies of deformed diatom valves mainly of Achnanthes spp. were recorded in contaminated sediments. In general, diatom taxocenoses presented a typical structure for non-contaminated environments. However, scarceness of specimens, lower S, and frequency of deformed valves suggest responses to metal contamination. For marine environments, the latter values corresponding to A. longipes may be considered a reliable reference to the response of benthic diatoms to metal contamination. Full article
(This article belongs to the Special Issue Bioaccumulation and Biomarkers Responses in Aquatic Organisms)
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Article
Research on Hypergeometric-Gaussian Vortex Beam Propagating under Oceanic Turbulence by Theoretical Derivation and Numerical Simulation
J. Mar. Sci. Eng. 2021, 9(4), 442; https://doi.org/10.3390/jmse9040442 - 19 Apr 2021
Cited by 2 | Viewed by 565
Abstract
In this paper, we use two methods to research the propagation characteristics of a Hypergeometric-Gaussian (HyGG) vortex beam under oceanic turbulence. One is numerical calculation based on the Rytov approximation theory, where the theoretical detection probability equation of the HyGG vortex beam propagating [...] Read more.
In this paper, we use two methods to research the propagation characteristics of a Hypergeometric-Gaussian (HyGG) vortex beam under oceanic turbulence. One is numerical calculation based on the Rytov approximation theory, where the theoretical detection probability equation of the HyGG vortex beam propagating through oceanic turbulence is derived. The other is numerical simulation based on random phase screens model of oceanic turbulence, where the influences generated by oceanic turbulence on the phase and intensity of the propagation beam as well as the propagation of the beam through several independent phase screens, kept at the same distance, have the same effect. The effects of oceanic turbulence parameters and initial beam parameters on the detection probability of the HyGG vortex beam at the receiver are discussed. The results of theoretical derivation are well in agreement with those of numerical simulation, which demonstrated that the numerical simulation method could effectively simulate the complex theoretical derivation. Both results show that with higher dissipation rate of kinetic energy per unit mass of fluid, smaller dissipation rate of mean-squared temperature and lower temperature-salinity contribution ratio comes the better detection probability. Meanwhile, a HyGG vortex beam with smaller topological charge and longer wavelength has a superior turbulent resistance property. It provides a promising way to estimate the propagation characteristics of the optical beams in an underwater environment. Full article
(This article belongs to the Section Physical Oceanography)
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Article
Simulation Modelling for Automated Guided Vehicle Introduction to the Loading Process of Ro-Ro Ships
J. Mar. Sci. Eng. 2021, 9(4), 441; https://doi.org/10.3390/jmse9040441 - 19 Apr 2021
Cited by 1 | Viewed by 777
Abstract
This paper aims to introduce the adaptation of automated guided vehicles (AGVs) in the car-loading process of Ro-Ro ships compared with the current loading process. This study analyzed the applicable scenarios for the AGVs’ adaptation in a Ro-Ro port, employing Arena simulation to [...] Read more.
This paper aims to introduce the adaptation of automated guided vehicles (AGVs) in the car-loading process of Ro-Ro ships compared with the current loading process. This study analyzed the applicable scenarios for the AGVs’ adaptation in a Ro-Ro port, employing Arena simulation to compare the productivity of the loading processes. The results revealed that the adaptation of the AGVs in the car-loading process of the Ro-Ro ships improves productivity and solves several problems of the current loading process. With 21 or more AGVs, the entire processing time is similar to or less than the current loading process, whereas, after 40 AGVs, it stayed the same. Furthermore, as the number of AGVs increases, the transfer time decreases, but the queue becomes longer. Identifying the effect of the AGV adaptation, this study provides valuable insights for developing the various traffic situations in Ro-Ro port operations. Full article
(This article belongs to the Special Issue Simulation Based Maritime Design)
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Article
Near-Inertial Waves Induced by Typhoon Megi (2010) in the South China Sea
J. Mar. Sci. Eng. 2021, 9(4), 440; https://doi.org/10.3390/jmse9040440 - 18 Apr 2021
Cited by 2 | Viewed by 739
Abstract
Near-inertial waves (NIWs) are a kind of internal wave, which are usually generated by synoptic wind forcing and play an important role in the oceanic energy budget. However, the lack of in situ observations limits our understanding of NIWs to some extent. Through [...] Read more.
Near-inertial waves (NIWs) are a kind of internal wave, which are usually generated by synoptic wind forcing and play an important role in the oceanic energy budget. However, the lack of in situ observations limits our understanding of NIWs to some extent. Through a comparison with in situ observations, in this study, we first showed that the hybrid coordinate ocean model reanalysis results could reasonably reproduce the typhoon-induced NIWs, and we then adopted these data to investigate the NIWs induced by typhoon Megi in 2010 in the South China Sea (SCS). The results indicate that Megi-induced near-inertial kinetic energy was mainly concentrated in the SCS Basin. In the vertical direction, Megi-induced NIWs could propagate to 1000 m depth. The damping and modal content of Megi-induced NIWs were site-dependent: In the region near Megi’s track, NIWs were dominated by the first three baroclinic modes and damped quickly; whereas in two zones to the west of the Luzon Island and Luzon Strait, the e-folding time of Megi-induced NIWs could be longer than 20 days and higher modes (mode-4 to mode-7) were enhanced several days after the passage of Megi. Possible mechanisms of these phenomena were also explored in this study. Full article
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Article
Particle-Swarm-Optimization-Enhanced Radial-Basis-Function-Kernel-Based Adaptive Filtering Applied to Maritime Data
J. Mar. Sci. Eng. 2021, 9(4), 439; https://doi.org/10.3390/jmse9040439 - 18 Apr 2021
Cited by 2 | Viewed by 792
Abstract
The real-life signals captured by different measurement systems (such as modern maritime transport characterized by challenging and varying operating conditions) are often subject to various types of noise and other external factors in the data collection and transmission processes. Therefore, the filtering algorithms [...] Read more.
The real-life signals captured by different measurement systems (such as modern maritime transport characterized by challenging and varying operating conditions) are often subject to various types of noise and other external factors in the data collection and transmission processes. Therefore, the filtering algorithms are required to reduce the noise level in measured signals, thus enabling more efficient extraction of useful information. This paper proposes a locally-adaptive filtering algorithm based on the radial basis function (RBF) kernel smoother with variable width. The kernel width is calculated using the asymmetrical combined-window relative intersection of confidence intervals (RICI) algorithm, whose parameters are adjusted by applying the particle swarm optimization (PSO) based procedure. The proposed RBF-RICI algorithm’s filtering performances are analyzed on several simulated, synthetic noisy signals, showing its efficiency in noise suppression and filtering error reduction. Moreover, compared to the competing filtering algorithms, the proposed algorithm provides better or competitive filtering performance in most considered test cases. Finally, the proposed algorithm is applied to the noisy measured maritime data, proving to be a possible solution for a successful practical application in data filtering in maritime transport and other sectors. Full article
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Article
Operational Analysis of Container Ships by Using Maritime Big Data
J. Mar. Sci. Eng. 2021, 9(4), 438; https://doi.org/10.3390/jmse9040438 - 18 Apr 2021
Viewed by 782
Abstract
The shipping company or the operator determines the mode of operation of a ship. In the case of container ships, there may be various operating patterns employed to arrive at the destination within the stipulated time. In addition, depending on the influence of [...] Read more.
The shipping company or the operator determines the mode of operation of a ship. In the case of container ships, there may be various operating patterns employed to arrive at the destination within the stipulated time. In addition, depending on the influence of the ocean’s environmental conditions, the speed and the route can be changed. As the ship’s fuel oil consumption is closely related to its operational pattern, it is possible to identify the most economical operations by analyzing the operational patterns of the ships. The operational records of each shipping company are not usually disclosed, so it is necessary to estimate the operational characteristics from publicly available data such as the automatic identification system (AIS) data and ocean environment data. In this study, we developed a visualization program to analyze the AIS data and ocean environmental conditions together and propose two categories of applications for the operational analysis of container ships using maritime big data. The first category applications are the past operation analysis by tracking previous trajectories, and the second category applications are the speed pattern analysis by shipping companies and shipyards under harsh environmental conditions. Thus, the operational characteristics of container ships were evaluated using maritime big data. Full article
(This article belongs to the Special Issue Simulation Based Maritime Design)
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Article
Mega-Ship-Generated Tsunami: A Field Observation in Tampa Bay, Florida
J. Mar. Sci. Eng. 2021, 9(4), 437; https://doi.org/10.3390/jmse9040437 - 18 Apr 2021
Viewed by 670
Abstract
The displacement of a large amount of water in a moderate-sized estuary by a fast-moving mega-ship can generate tsunami-like waves. Such waves, generated by cruise ships, were observed in Tampa Bay, Florida, USA. Two distinct, long tsunami-like waves were measured, which were associated [...] Read more.
The displacement of a large amount of water in a moderate-sized estuary by a fast-moving mega-ship can generate tsunami-like waves. Such waves, generated by cruise ships, were observed in Tampa Bay, Florida, USA. Two distinct, long tsunami-like waves were measured, which were associated with the passage of a large cruise ship. The first wave had a period of 5.4 min and a height of 0.40 m near the shoreline. The second wave had a period of 2.5 min and was 0.23 m high. The peak velocity of the onshore flow during the second wave reached 0.65 m/s. The shorter, second wave propagated considerably faster than the first wave in the breaking zone. The measured wave celerity was less than 50% of the calculated values, using the shallow water approximation of the dispersion equation, suggesting that nonlinear effects play an important role. A fundamental similarity among the generation of tsunamis, as induced by mega-ships, landslides or earthquakes, is a process that causes a vertical velocity at the sea surface, where a freely propagating wave is produced. This mega-ship-generated tsunami provides a prototype field laboratory for systematically studying tsunami dynamics, particularly the strong turbulent flows associated with the breaking of a tsunami wave in the nearshore, and tsunami–land interactions. It also provides a realistic demonstration for public education, which is essential for the preparation and management of this unpreventable hazard. Full article
(This article belongs to the Special Issue Modeling Waves Generated by Tsunamigenic Source)
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Article
Effects of Sound from Seismic Surveys on Fish Reproduction, the Management Case from Norway
J. Mar. Sci. Eng. 2021, 9(4), 436; https://doi.org/10.3390/jmse9040436 - 17 Apr 2021
Viewed by 842
Abstract
Anthropogenic noise has been recognized as a source of concern since the beginning of the 1940s and is receiving increasingly more attention. While international focus has been on the effects of noise on marine mammals, Norway has managed seismic surveys based on the [...] Read more.
Anthropogenic noise has been recognized as a source of concern since the beginning of the 1940s and is receiving increasingly more attention. While international focus has been on the effects of noise on marine mammals, Norway has managed seismic surveys based on the potential impact on fish stocks and fisheries since the late 1980s. Norway is, therefore, one of very few countries that took fish into account at this early stage. Until 1996, spawning grounds and spawning migration, as well as areas with drifting eggs and larvae were recommended as closed for seismic surveys. Later results showed that the effects of seismic surveys on early fish development stages were negligible at the population level, resulting in the opening of areas with drifting eggs and larvae for seismic surveys. Spawning grounds, as well as concentrated migration towards these, are still closed to seismic surveys, but the refinement of areas and periods have improved over the years. Since 2018, marine mammals have been included in the advice to management. The Norwegian case provides a clear example of evidence-based management. Here, we examine how scientific advancements informed the development of Norwegian management and how management questions were incorporated into new research projects in Norway. Full article
(This article belongs to the Special Issue Ocean Noise: From Science to Management)
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Article
Innovation Concept Model and Prototype Validation of Robotic Fish with a Spatial Oscillating Rigid Caudal Fin
J. Mar. Sci. Eng. 2021, 9(4), 435; https://doi.org/10.3390/jmse9040435 - 17 Apr 2021
Viewed by 675
Abstract
Inspired by carangiform fish with a high-aspect ratio of the caudal fin’s up-down swing, but also by dolphins with a similar caudal fin’s left-right swing, a robotic fish with a spatial oscillating rigid caudal fin is implemented to optimize propulsion and maneuverability, whose [...] Read more.
Inspired by carangiform fish with a high-aspect ratio of the caudal fin’s up-down swing, but also by dolphins with a similar caudal fin’s left-right swing, a robotic fish with a spatial oscillating rigid caudal fin is implemented to optimize propulsion and maneuverability, whose orientation could be transformed to any position of a taper domain. First, three steering-engines were adopted to make the conceptual prototype, and an experimental apparatus for measuring thrust, lift forces, lateral forces and torque was developed. Then, three comparison experiments, respectively corresponding to the three modes of cruise, diving and maneuvering in random space, were conducted to imitate bionic fish’s hydrodynamics. The comparison results of the experiments proved that propelling and maneuvering in any direction could be realized through changing the orientation of the spatial oscillating rigid caudal fin. Full article
(This article belongs to the Special Issue Advanced Technologies for Maritime and Underwater Archaeology)
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Article
Effect of Boundary Conditions on Fluid–Structure Coupled Modal Analysis of Runners
J. Mar. Sci. Eng. 2021, 9(4), 434; https://doi.org/10.3390/jmse9040434 - 17 Apr 2021
Viewed by 581
Abstract
To predict the resonance characteristics of hydraulic machinery, it is necessary to accurately calculate the natural modes of the runners in the operating environment. However, in the existing research, the boundary conditions of the numerical modal analysis of the runner were not unified. [...] Read more.
To predict the resonance characteristics of hydraulic machinery, it is necessary to accurately calculate the natural modes of the runners in the operating environment. However, in the existing research, the boundary conditions of the numerical modal analysis of the runner were not unified. In this paper, numerical modal analysis of a prototype Francis pump turbine runner was carried out using the acoustic–structure coupling method. The results of three different constraints were compared. The influence of the energy loss on the chamber wall on the natural modes of the runner was studied by the absorption boundary. The results show that the constraint condition (especially the rotating shaft) has significant impacts on the torsional mode, the radial mode, the 1 nodal-diameter mode, and the 0 nodal-circle mode, and the maximum differences in the natural frequencies under different conditions are 69.3%, 56.4%, 35.1%, and 9.4%, respectively. The change of the natural frequencies is closely related to the modal shapes. On the other hand, the energy loss on the wall mainly affects the nodal-circle modes, and the influence on other modes is negligible. The results can provide references for the design and resonance characteristics analysis of hydraulic machinery runners. Full article
(This article belongs to the Special Issue Fluid/Structure Interactions)
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Review
Research Progress in Transfer, Accumulation and Effects of Microplastics in the Oceans
J. Mar. Sci. Eng. 2021, 9(4), 433; https://doi.org/10.3390/jmse9040433 - 17 Apr 2021
Cited by 1 | Viewed by 987
Abstract
One of the major concerns regarding the presence of plastics in ocean environments are the effects on marine biota. Plastics can be distinguished in macro- (≥25 mm), meso- (<25 mm–5 mm) micro- (<5 mm–1 µm), and nano-plastic (<1 µm) and are practically omnipresent [...] Read more.
One of the major concerns regarding the presence of plastics in ocean environments are the effects on marine biota. Plastics can be distinguished in macro- (≥25 mm), meso- (<25 mm–5 mm) micro- (<5 mm–1 µm), and nano-plastic (<1 µm) and are practically omnipresent in aquatic habitats and subject to long-range transport. The purpose of this review is to report the last findings on the release, transfer, accumulation, and effects of micro-plastics, MPs, in the oceans. MPs have the chance to adsorb different kind of organisms and compounds on their outer surface, including bacteria, viruses, algae, and abiotic substances. In this way, they can cause sever hazard once they enter the food chain. Their harm to higher organisms is discussed as well as main routes of MPs–organism interactions, i.e., ventilation, and ingestion. Potential effects on populations, communities, and ecosystems and uptake routes and transition into tissues are discussed. In consideration of the potential threats of plastic particles to ecological functions and human health risks, we recommend specific directions of future research approaches. Full article
(This article belongs to the Special Issue Microplastic Pollution in the Ocean)
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Article
Impacts of Plastic-Made Packaging on Marine Key Species: Effects Following Water Acidification and Ecological Implications
J. Mar. Sci. Eng. 2021, 9(4), 432; https://doi.org/10.3390/jmse9040432 - 17 Apr 2021
Cited by 1 | Viewed by 721
Abstract
This study evaluates the impacts of 16 different leachates of plastic-made packaging on marine species of different trophic levels (bacteria, algae, echinoderms). Standard ecotoxicological endpoints (inhibition of bioluminescence, inhibition of growth, embryo-toxicity) and alterations of ecologically significant parameters (i.e., echinoderms’ body-size) were measured [...] Read more.
This study evaluates the impacts of 16 different leachates of plastic-made packaging on marine species of different trophic levels (bacteria, algae, echinoderms). Standard ecotoxicological endpoints (inhibition of bioluminescence, inhibition of growth, embryo-toxicity) and alterations of ecologically significant parameters (i.e., echinoderms’ body-size) were measured following exposure under different pH water conditions: marine standard (pH 8.1) and two increasingly acidic conditions (pH 7.8 and 7.5) in order to evaluate possible variations induced by ocean acidification. The results obtained in this study evidence that the tested doses are not able to significantly affect bacteria (Vibrio fischeri) and algae (Phaeodactylum tricornutum). On the contrary, Paracentrotus lividus larvae were significantly affected by several packaging types (13 out of 16) with meaningless differences between pH conditions. Full article
(This article belongs to the Special Issue Marine Litter)
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Article
Soil Classification and Site Variability Analysis Based on CPT—A Case Study in the Yellow River Subaquatic Delta, China
J. Mar. Sci. Eng. 2021, 9(4), 431; https://doi.org/10.3390/jmse9040431 - 16 Apr 2021
Cited by 1 | Viewed by 573
Abstract
The Yellow River Delta is located at the junction of the Yellow River and Bohai. The impact function from the river and the dynamics of the ocean tides make the soil composition and distribution in this area substantially complicated. In order to test [...] Read more.
The Yellow River Delta is located at the junction of the Yellow River and Bohai. The impact function from the river and the dynamics of the ocean tides make the soil composition and distribution in this area substantially complicated. In order to test the distribution and variation of the soil layers in the Yellow River Delta, the soil layers in the test area were classified and the variation was calculated using the cone penetration test (CPT). The following conclusions were drawn: (1) the soil in the measured area is mainly composed of sensitive fine-grained soil, accounting for about 70% of all soil types, and the content of sensitive fine-grained soil in the far-sea position is higher than that in the offshore position in the direction perpendicular to the coastline. (2) It has a high vertical variability index (VVI) at the near-shore location, above 45%, and a low vertical variability at the far coast, generally below 20%. (3) The horizontal variability index (HVI) changes significantly near the coast, and it remains below 45% in the test area. Full article
(This article belongs to the Special Issue Coastal Engineering: Sustainability and New Technologies)
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Article
Endophytic Fungi of Emersed Halophytes in River Deltas and Tidal Flats of the Korean Ramsar Wetlands
J. Mar. Sci. Eng. 2021, 9(4), 430; https://doi.org/10.3390/jmse9040430 - 15 Apr 2021
Viewed by 754
Abstract
This study aimed to obtain information on the diversity and distribution of the endophytic fungi in Ramsar wetlands. Vast salt marshes in Suncheon Bay, Korea, are formed by two types of ecotones (tidal flats and deltas) that are supported by the emersed halophytes [...] Read more.
This study aimed to obtain information on the diversity and distribution of the endophytic fungi in Ramsar wetlands. Vast salt marshes in Suncheon Bay, Korea, are formed by two types of ecotones (tidal flats and deltas) that are supported by the emersed halophytes Phragmites australis and Suaeda japonica. Overall, 324 endophytes were isolated from P. australis (six sampling points in the delta and five in the tidal flats) and S. japonica (six in tidal flats). Margalef’s, Menhinick’s, Shannon’s, and Simpson’s diversity indices significantly varied among the ecotones. In particular, higher variance in diversity value and unevenness was observed in the delta marsh compared with the tidal flat marsh. Further, morphological diversity in the delta salt marsh was 1.8 times higher than that of the tidal flat. Comprising several dominant genera (Aspergillus, Cladosporium, and Penicillium), Epicoccum, Paraconiothyrium, Septoriella, and Talaromyces were widely distributed regardless of the aquatic conditions or halophyte species. This study highlights the distinct distribution and diversity of marine endophytes in various ecotones that can physically protect the coastal areas. This data is of much value to secure a national culture collection for future restoration of the coastal wetlands and their ecosystems. Full article
(This article belongs to the Special Issue Coastal Wetlands)
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Article
The Effects of Installation on the Elastic Stiffness Coefficients of Spudcan Foundations
J. Mar. Sci. Eng. 2021, 9(4), 429; https://doi.org/10.3390/jmse9040429 - 15 Apr 2021
Cited by 1 | Viewed by 505
Abstract
Subjected to pre-load, spudcan foundations, widely utilized to support offshore jack-up rigs, may penetrate in a few diameters into soft clays before mobilizing sufficient resistance from soil. While its stress–strain behavior is known to be affected by the embedment condition and soil backflow, [...] Read more.
Subjected to pre-load, spudcan foundations, widely utilized to support offshore jack-up rigs, may penetrate in a few diameters into soft clays before mobilizing sufficient resistance from soil. While its stress–strain behavior is known to be affected by the embedment condition and soil backflow, the small-strain calculation with wished-in-place assumption was previously adopted to analyze its elastic stiffness coefficients. This study takes advantage of a recently developed dual-stage Eulerian–Lagrangian (DSEL) technique to re-evaluate the elastic stiffness coefficients of spudcans after realistically modelling the deep, continuous spudcan penetration. A numerical parametric exercise is conducted to investigate the effects of strength non-homogeneity, embedment depths, and the spudcan’s size on the elastic stiffness. On these bases, an expression is provided such that the practicing engineers can conveniently factor the installation effects into the estimation of elastic stiffness coefficients of spudcans. Full article
(This article belongs to the Special Issue Structure-Seabed Interactions in Marine Environments)
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Article
A Velocity Obstacle-Based Real-Time Regional Ship Collision Risk Analysis Method
J. Mar. Sci. Eng. 2021, 9(4), 428; https://doi.org/10.3390/jmse9040428 - 15 Apr 2021
Cited by 4 | Viewed by 599
Abstract
Maritime accidents such as ship collisions pose continuous risks to individuals and society with due to their severe consequences on human life, economic and environmental losses, etc. Supervising the maritime traffic in the different regions and maintaining its safety level is an essential [...] Read more.
Maritime accidents such as ship collisions pose continuous risks to individuals and society with due to their severe consequences on human life, economic and environmental losses, etc. Supervising the maritime traffic in the different regions and maintaining its safety level is an essential task for stakeholders such as maritime safety administrations. In this research, a new ship collision risk analysis method is developed with the utilisation of AIS (Automatic Identification System) data. A velocity obstacle-based risk measurement is applied to measure the risk of collision between multiple ships from the velocity perspective, based on which, the collision risk and the complexity of the encounter situation are obtained at the same time. Secondly, a density-based clustering technique is introduced to identify the hotspots of ship traffic in the region as an indicator for maritime safety operators. A case study using historical AIS data was implemented to verify the effectiveness of the proposed approach in a manner that simulates the real-time data scenario. Furthermore, a comparison between existing risk analysis method is conducted to validate the proposed method. Full article
(This article belongs to the Section Ocean Engineering)
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Article
High-Frequency Radar Cross Section of Ocean Surface for an FMICW Source
J. Mar. Sci. Eng. 2021, 9(4), 427; https://doi.org/10.3390/jmse9040427 - 15 Apr 2021
Viewed by 494
Abstract
The frequency-modulated interrupted continuous waveform (FMICW) has been widely used in remotely sensing sea surface states by high-frequency ground wave radar (HFGWR). However, the radar cross section model of the sea surface for this waveform has not yet been presented. Therefore, the first- [...] Read more.
The frequency-modulated interrupted continuous waveform (FMICW) has been widely used in remotely sensing sea surface states by high-frequency ground wave radar (HFGWR). However, the radar cross section model of the sea surface for this waveform has not yet been presented. Therefore, the first- and second-order cross section models of the sea surface about this waveform are derived in this study. The derivation begins with the general electric field equations. Subsequently, the FMICW source is introduced as the radar transmitted signal to obtain the FMICW-incorporated backscattered electric field equations. These equations are used to calculate range spectra by Fourier transforming. Therefore, Fourier transformation of the range spectra calculated from successive sweep intervals gives the Doppler spectra or the power spectral densities. The radar cross section model is obtained by directly comparing the Doppler spectra with the standard radar range equation. Moreover, the derived first- and second-order radar cross section models for an FMICW source are simulated and compared with those for a frequency-modulated continuous waveform (FMCW) source. Results show that the cross section models for the FMICW and FMCW cases have different analytical expressions but almost the same numerical results. Full article
(This article belongs to the Special Issue Development of Oceanographic Sensors)
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Article
Multiple Submerged Tidal Notches: A Witness of Sequences of Coseismic Subsidence in the Aegean Sea, Greece
J. Mar. Sci. Eng. 2021, 9(4), 426; https://doi.org/10.3390/jmse9040426 - 14 Apr 2021
Viewed by 541
Abstract
In some islands of the Aegean, there is evidence of the occurrence of repeated rapid subsidences during the Late Holocene. In this paper, the shape of tidal notches that may be well-preserved underwater is recalled in order to reconstruct sequences of coseismic subsidences [...] Read more.
In some islands of the Aegean, there is evidence of the occurrence of repeated rapid subsidences during the Late Holocene. In this paper, the shape of tidal notches that may be well-preserved underwater is recalled in order to reconstruct sequences of coseismic subsidences and other relative sea-level changes, which occurred during, at least, the last few millennia. A reanalysis of the published measurements of submerged tidal notches in several islands reveals that subsidence trends in many areas of the Aegean are not continuous with gradual movement but, also, are the result of repeated coseismic vertical subsidences of some decimetres at each time. The estimated average return times are of the order of approximately some centuries to one millennium. Although the results cannot be used for short-term predictions of earthquakes, they may provide useful indications on the long-term tectonic trends that are active in the Aegean region. Full article
(This article belongs to the Special Issue Tectonics and Sea-Level Fluctuations)
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Article
Tidal Energy Round Robin Tests: A Comparison of Flow Measurements and Turbine Loading
J. Mar. Sci. Eng. 2021, 9(4), 425; https://doi.org/10.3390/jmse9040425 - 14 Apr 2021
Cited by 5 | Viewed by 691
Abstract
A Round Robin Tests program is being undertaken within the EC MaRINET2 initiative. This programme studies the used facility influence can have on the performance evaluation of a horizontal axis tidal turbine prototype when it is operated under wave and current conditions. In [...] Read more.
A Round Robin Tests program is being undertaken within the EC MaRINET2 initiative. This programme studies the used facility influence can have on the performance evaluation of a horizontal axis tidal turbine prototype when it is operated under wave and current conditions. In this paper, we present the design of experiments that is used throughout the work programme and the results related to the flow characterisation obtained at the Ifremer wave and current circulating tank, the Cnr-Inm wave towing tank and the ocean research facility FloWave. These facilities have been identified to provide adequate geometric conditions to accommodate a 0.724 m diameter turbine operating at flow velocities of 0.8 and 1.0 m/s. The set-up is replicated in each of the facilities with exemption of the amount of flow measuring instruments. Intrinsic differences in creating wave and currents between facilities are found. Flow velocities are up to 10% higher than the nominal values and wave amplitudes higher than the target values by up to a factor of 2. These discrepancies are related to the flow and wave generation methods used at each facility. When the flow velocity is measured besides the rotor, the velocity presents an increase of 8% compared to the upstream measurements. Full article
(This article belongs to the Special Issue Marine Renewables–Infrastructures and Physical Testing)
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Article
Hydrodynamic Analysis of a Modular Floating Structure with Tension-Leg Platforms and Wave Energy Converters
J. Mar. Sci. Eng. 2021, 9(4), 424; https://doi.org/10.3390/jmse9040424 - 14 Apr 2021
Viewed by 479
Abstract
This work presents a modular floating structure, which consists of five inner tension-leg platforms and two outermost wave energy converters (denoted as MTLPW). The hydrodynamic interaction effect and the mechanical coupling effect between the five inner tension-leg platforms (TLP) and the two outermost [...] Read more.
This work presents a modular floating structure, which consists of five inner tension-leg platforms and two outermost wave energy converters (denoted as MTLPW). The hydrodynamic interaction effect and the mechanical coupling effect between the five inner tension-leg platforms (TLP) and the two outermost wave energy converters (WEC) are taken into consideration. The effects of the connection modes and power take-off (PTO) parameters of the WECs on the hydrodynamic performance of the MTLPW system are investigated under both operational and extreme sea conditions. The results indicate that the hydrodynamic responses of the MTLPW system are sensitive to the connection type of the outermost WECs. The extreme responses of the bending moment of connectors depend on the number of continuously fixed modules. By properly utilizing hinge-type connectors to optimize the connection mode for the MTLPW system, the effect of more inner TLP modules on the hydrodynamic responses of the MTLPW system can be limited to be acceptable. Therefore, the MTLPW system can be potentially expanded to a large degree. Full article
(This article belongs to the Special Issue Recent Advances in Floating Structures)
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Article
The Importance of Geotechnical Evaluation and Shoreline Evolution in Coastal Vulnerability Index Calculations
J. Mar. Sci. Eng. 2021, 9(4), 423; https://doi.org/10.3390/jmse9040423 - 14 Apr 2021
Cited by 2 | Viewed by 2379
Abstract
The aim of this specific study is to present a new weighted Coastal Vulnerability Index (CVIWF), with an emphasis given to the geotechnical evaluation and shoreline evolution rate measured through high-resolution remote sensing, which seem to be the most interfering variables [...] Read more.
The aim of this specific study is to present a new weighted Coastal Vulnerability Index (CVIWF), with an emphasis given to the geotechnical evaluation and shoreline evolution rate measured through high-resolution remote sensing, which seem to be the most interfering variables in CVI calculations. As a pilot area for the application of the new CVIWF, the Gulf of Patras in Western Greece was selected, which is suffering erosion problems due to climate change, the sea level rising and human intervention. The new CVIWF, which was applied in this research, includes the following innovations: (1) the use of geotechnical characterization instead of geological–geomorphological characterization, (2) the use of high-resolution remote sensing data for the detection of shoreline evolution rate and (3) the insertion of a specific weighted geotechnical factor in the CVIWF formula. The results from the application of the unweighted CVI show that percentages of 20.13%, 20.47%, 24.56%, 29.39% and 5.45% of the gulf’s shoreline are under the regime of very low, low, moderate, high and very high vulnerability, respectively. On the other hand, the corresponding results from the application of the weighted CVIWF show a percentage of 14.59%, 25.91%, 20.04, 36.48% and 2.98, respectively. Full article
(This article belongs to the Special Issue Novel Technologies and Solutions for Coastal Evolution and Management)
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Article
Analysis of Dangerous Sea States in the Northwestern Mediterranean Area
J. Mar. Sci. Eng. 2021, 9(4), 422; https://doi.org/10.3390/jmse9040422 - 14 Apr 2021
Cited by 1 | Viewed by 497
Abstract
Extreme sea waves, although rare, can be notably dangerous when associated with energetic sea states and can generate risks for the navigation. In the last few years, they have been the object of extensive research from the scientific community that helped with understanding [...] Read more.
Extreme sea waves, although rare, can be notably dangerous when associated with energetic sea states and can generate risks for the navigation. In the last few years, they have been the object of extensive research from the scientific community that helped with understanding the main physical aspects; however, the estimate of extreme waves probability in operational forecasts is still debated. In this study, we analyzed a number of sea-states that occurred in a precise area of the Mediterranean sea, near the location of a reported accident, with the objective of relating the probability of extreme events with different sea state conditions. For this purpose, we performed phase-resolving simulations of wave spectra obtained from a WaveWatch III hindcast, using a Higher Order Spectral Method. We produced statistics of the sea-surface elevation field, calculating crest distributions and the probability of extreme events from the analysis of a long time-series of the surface elevation. We found a good matching between the distributions of the numerically simulated field and theory, namely Tayfun second- and third- order ones, in contrast with a significant underestimate given by the Rayleigh distribution. We then related spectral quantities like angular spreading and wave steepness to the probability of occurrence of extreme events finding an enhanced probability for high mean steepness seas and narrow spectra, in accordance with literature results, finding also that the case study of the reported accident was not amongst the most dangerous. Finally, we related the skewness and kurtosis of the surface elevation to the wave steepness to explain the discrepancy between theoretical and numerical distributions. Full article
(This article belongs to the Special Issue Extreme Waves)
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Article
A Barotropic Solver for High-Resolution Ocean General Circulation Models
J. Mar. Sci. Eng. 2021, 9(4), 421; https://doi.org/10.3390/jmse9040421 - 14 Apr 2021
Viewed by 505
Abstract
High-resolution global ocean general circulation models (OGCMs) play a key role in accurate ocean forecasting. However, the models of the operational forecasting systems are still not in high resolution due to the subsequent high demand for large computation, as well as the low [...] Read more.
High-resolution global ocean general circulation models (OGCMs) play a key role in accurate ocean forecasting. However, the models of the operational forecasting systems are still not in high resolution due to the subsequent high demand for large computation, as well as the low parallel efficiency barrier. Good scalability is an important index of parallel efficiency and is still a challenge for OGCMs. We found that the communication cost in a barotropic solver, namely, the preconditioned conjugate gradient (PCG) method, is the key bottleneck for scalability due to the high frequency of the global reductions. In this work, we developed a new algorithm—a communication-avoiding Krylov subspace method with a PCG (CA-PCG)—to improve scalability and then applied it to the Nucleus for European Modelling of the Ocean (NEMO) as an example. For PCG, inner product operations with global communication were needed in every iteration, while for CA-PCG, inner product operations were only needed every eight iterations. Therefore, the global communication cost decreased from more than 94.5% of the total execution time with PCG to less than 63.4% with CA-PCG. As a result, the execution time of the barotropic modes decreased from more than 17,000 s with PCG to less than 6000 s with CA-PCG, and the total execution time decreased from more than 18,000 s with PCG to less than 6200 s with CA-PCG. Besides, the ratio of the speedup can also be increased from 3.7 to 4.6. In summary, the high process count scalability when using CA-PCG was effectively improved from that using the PCG method, providing a highly effective solution for accurate ocean simulation. Full article
(This article belongs to the Special Issue Ocean Modelling in Support of Operational Ocean and Coastal Services)
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Article
From the Reef to the Ocean: Revealing the Acoustic Range of the Biophony of a Coral Reef (Moorea Island, French Polynesia)
J. Mar. Sci. Eng. 2021, 9(4), 420; https://doi.org/10.3390/jmse9040420 - 13 Apr 2021
Viewed by 868
Abstract
The ability of different marine species to use acoustic cues to locate reefs is known, but the maximal propagation distance of coral reef sounds is still unknown. Using drifting antennas (made of a floater and an autonomous recorder connected to a hydrophone), six [...] Read more.
The ability of different marine species to use acoustic cues to locate reefs is known, but the maximal propagation distance of coral reef sounds is still unknown. Using drifting antennas (made of a floater and an autonomous recorder connected to a hydrophone), six transects were realized from the reef crest up to 10 km in the open ocean on Moorea island (French Polynesia). Benthic invertebrates were the major contributors to the ambient noise, producing acoustic mass phenomena (3.5–5.5 kHz) that could propagate at more than 90 km under flat/calm sea conditions and more than 50 km with an average wind regime of 6 knots. However, fish choruses, with frequencies mainly between 200 and 500 Hz would not propagate at distances greater than 2 km. These distances decreased with increasing wind or ship traffic. Using audiograms of different taxa, we estimated that fish post-larvae and invertebrates likely hear the reef at distances up to 0.5 km and some cetaceans would be able to detect reefs up to more than 17 km. These results are an empirically based validation from an example reef and are essential to understanding the effect of soundscape degradation on different zoological groups. Full article
(This article belongs to the Special Issue Passive Acoustics to Study Marine and Freshwater Ecosystems)
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