Marine Structures Research Articles

Investigating the Synergistic Corrosion Protection Effect of an Alloy Element and Corrosion Inhibitor on Steel Reinforcement Using Machine Learning and Electrochemical Impedance Spectroscopy

Steel reinforcement in marine concrete structures is vulnerable to chloride-induced corrosion, which compromises its structural integrity and durability. This study explores the combined effect of the alloying element Cr and the smart corrosion inhibitor LDH-NO2 on enhancing the corrosion resistance of steel reinforcement. Employing a machine learning approach with a support vector machine (SVM) algorithm, a predictive model was developed to estimate the polarization resistance of steel, considering Cr content, LDH-NO2 dosage, environmental pH, and chloride concentration. The model was rigorously trained and validated, demonstrating high accuracy, with a correlation coefficient exceeding 0.85. The findings reveal that the addition of Cr and application of LDH-NO2 synergistically improve corrosion resistance, with the model providing actionable insights for selecting effective corrosion protection methods in diverse concrete environments.

On the study of a body force model for a jetting type breakwater

The introduction of jetting-type floating breakwaters can significantly enhance the performance of large floating marine structures. Especially, this novel technology may effectively handle traditional breakwaters' bottleneck, namely, weak wave dissipation performance under large period waves. In this paper, a new method is established using body force model, in conjunction with a computational fluid dynamics solver and dynamic overlapping mesh technology, to simulate jetting-type floating breakwaters. The mathematical model is elucidated in the context of fluid mechanics, propellers body force model, and floating breakwaters’ geometric aspects. The method is proved to be compact and flexible in terms of implementation, offering advantages for the simulation of floating breakwaters employing hydraulic systems. Moreover, the new method can resolve low efficiency during computation, normally caused by fine local flows when simulating long-range jetting-type floating breakwaters: By controlling parameters precisely, it simulates accelerating local flows, high-speed water-jets, and it offers efficient visualization of the water-jets and their effects on floating breakwaters. Results show that the novel jetting-type floating breakwater significantly enhances wave dissipation. A comparison is performed between the novel breakwater against the typical example of square box floating breakwater with same dimensions and under wave incidence, thus the accuracy of the method was verified likewise. This research provides a new numerical method for jetting technologies applied to floating breakwaters and porous structures, also offering valuable insights for new types of wave dissipation methods.

Durability of SFCB reinforced low-alkalinity seawater sea sand concrete beams in marine environment

Seawater sea-sand concrete (SWSSC) provides an alternative to normal concrete, while Steel-FRP Composite Bars (SFCB) offer corrosion resistance in offshore and marine structures. Despite their benefits, the long-term performance of SFCB-reinforced SWSSC structures remains under-explored. This study evaluated the durability of such beams, particularly focusing on the effects of using Portland cement versus low-alkalinity calcium sulphoaluminate (CSA) cement. The investigation involved tensile and pull-out tests conducted on SFCB, and flexural tests conducted on the beam components after accelerated marine environmental exposure over periods ranging from one to six months. Results highlighted that SFCB embedded in low-alkalinity CSA cement exhibited improved retention of tensile strength, elastic modulus, and bonding strength by 32.0 %, 39.1 %, and 56.7 % respectively, compared to that embedded in normal Portland cement concrete. Microstructural analyses showed much less hydrolysis of the resin matrix and shallower corrosion of the basalt FRP (BFRP) cover on the SFCB. Furthermore, flexural tests demonstrated superior cooperative performance between low-alkalinity CSA concrete with SFCB in beam components, showing only marginal degradation in crack density, crack strength, and yielding points. The ultimate failure load of beams made with CSA concrete was 1.89 times higher than those made with normal SWSSC after 6 months of exposure. These results underscore the potential of low-alkalinity concrete in improving the long-term durability and structural performance of SFCB-reinforced marine concrete infrastructures.

Prediction of Pier Scour Depth under Extreme Typhoon Storm Tide

The Western Pacific region is highly vulnerable to typhoon storm surge disasters, with localized erosion posing a particularly prominent issue for coastal marine structures. The prevalence of extreme typhoon storm surges poses a significant threat to the safety of engineering projects in these areas. In this study, a parameterized wind field model with precise calculation of wind speed was employed to establish a numerical model for typhoon storm tides. Based on the Western Pacific typhoon data from 1949 to 2023, hydraulic simulations were conducted for Hangzhou Bay, Xiangshan Port, and Yueqing Bay, revealing maximum flow velocities of 4.5 m/s, 1.95 m/s, and 2.09 m/s, respectively. These velocities exceeded the maximum possible tidal flow by 0.47–1.17 m/s. Additionally, using Sun’s velocity formula, the initiation flow velocities were calculated to be 1.85 m/s, 1.81 m/s, and 2.06 m/s for the aforementioned locations. Through localized erosion tests conducted around typical bridge piers and the subsequent application of similarity criteria, the maximum depth of localized erosion in the study area was determined to range from 2.16 m to 16.1 m, which corresponds to 1.1–2.3 times the scour caused by the maximum tidal flow scenario. A comparison of the erosion test results with calculations based on several formulas demonstrated that the scour prediction formula proposed by Sun exhibited the highest accuracy. This study supplements the understanding of the impact of typhoon storm surges on bridge pier erosion and provides a scientific basis for the design of bridge foundations.

A novel strategy for design of mechanically robust antifouling coatings via bifunctional domain engineering

The issue of biofouling on marine structures carries significant economic and ecological implications, necessitating the development of effective and durable antifouling coatings. Traditional organic antifouling coatings often struggle with mechanical robustness in harsh marine environments, making them fragile and highly susceptible to abrasion. To address these challenges, we propose a novel “bifunctional domain engineering” strategy for designing robust antifouling coatings that combines excellent mechanical strength of a Fe-based amorphous layer and high antifouling efficacy of an incorporated organics. The hard domains consist of Fe-based amorphous micro humps, providing a sturdy framework that enhances the coating's mechanical durability. In contrast, the soft domains comprise epoxy resin infused with Cu2O and 4,5-Dichloro-2-n-octyl-4-isothiazolin-3-one (DCOIT), offering a dual-action antifouling function via controllable antifouling agent release. Evaluation of antifouling performance by lab tests against Pseudomonas aeruginosa, Staphylococcus aureus, and Chlorella algae and practical marine field tests (for 150 days) demonstrates significant reductions in bacterial and algal adhesion (nearly 100 % resistance) with the bifunctional domain engineered coating (referred to as HSR coating), compared to pure amorphous coating. Mechanical durability tests, including abrasion and erosion experiments, underscore the HSR coating's excellent wear resistance. Importantly, the HSR coating maintains its outstanding antifouling properties even after 1000 abrasion cycles, highlighting its potential for long-term marine applications in harsh conditions. This study lays the groundwork for design of robust antifouling coatings capable of withstanding the harsh operating environments while effectively combating biofouling.

On the long-term fatigue analysis of marine structures

This paper investigates the performance of several procedures available in literature used to evaluate the multi-dimensional integral associated with long-term fatigue assessment of marine structures. Direct integration methods, Monte Carlo-based approaches and Dimension-Reduction methods are investigated. The focus is on solving the four-dimensional integral for wave-induced fatigue cases when wind-sea and swell waves are simultaneously considered in the analysis. Although the procedures investigated can be used either for time-domain or frequency-domain fatigue approaches, all fatigue analyses performed in this work are restricted to the frequency-domain and are based on idealized stress transfer functions that attempt to mimic the complex behavior of some marine structures. To evaluate the performance of these methodologies, different transfer functions of unimodal and bimodal types are studied. The long-term fatigue damages are calculated using all the investigated methods, and their accuracies and efficiencies are compared. It is found that the efficiency of Monte Carlo Simulation-based methods is problem-dependent and may require many numerical simulations to achieve good accuracy for some cases. Additionally, the Dimension-Reduction methods can lead to highly suitable results with a very low number of integration points and, among all methods investigated, the BDRM (Bivariate Dimension-Reduction Method) stands out due to its excellent performance.

Impact resistance of recycled-PET fiber strengthened wave-dissipating concrete block considering rocking motion

This study was conducted to enhance the impact resistance of wave-dissipating concrete blocks by recycled-Polyethylene Terephthalate (rPET) fibers. The aim of this study is to address the structural vulnerabilities of maritime structures and contribute to environmental issue. Traditionally, the stability of marine structures has been largely dependent on self-weight, a characteristic that can be undermined by damage from sea waves. Wave-dissipating concrete blocks are engineered to reduce the power of waves, but they remain susceptible to fractures caused by hoisting and rocking motions after installation. Existing evaluations often neglect the impact of rocking motion, primarily concentrating on fractures due to lifting. To enhance impact resistance, ultra-slow speed experimental tests were conducted to determine the fracture energy of concrete block considering rPET. The results revealed a significant improvement in the fracture energy of rPET reinforced concrete. Based on these experimental test results, a numerical model was developed to simulate the behavior of wave-dissipating concrete blocks considering rocking motion. The developed Smoothed Particle Hydrodynamics (SPH) model proved to be more relevant than the Finite Element (FE) model. Furthermore, this newly developed numerical model was utilized to evaluate structural performance. The results of the numerical analysis indicated a relationship between weight and impact velocity on the occurrence of damage. This led to the proposal of fragility curves for Sealock and TTP under various impact velocities during rocking motion. Fragility curves, developed based on impact velocity, demonstrated enhanced impact resistance of wave-dissipating concrete blocks reinforced with rPET. In addition, the incorporation of PET fibers effectively controlled crack propagation and improved impact resistance, particularly with increasing block weight. The methodology employed in this study holds potential for predicting outcomes using simple data, making it applicable to other scenarios such as vehicle-bridge pier collisions.

Nonlinear Soil–Pile–Structure Interaction Behaviour of Marine Jetty Structures

Nonlinear soil–pile–structure interaction (SPSI) phenomena are known to play a vital role in the response of bottom-fixed marine structures. For such structures, these phenomena are commonly considered by the imposition of p-y, τ-z, and q-z springs, representing the lateral and axial shaft and axial base soil resistances, respectively. The importance of each resistance mechanism depends on the type of foundation system, with only very limited studies investigating their roles in the response of piled marine structures, such as jetties. Within this context, this study presents numerical three-dimensional pushover analysis results for two marine jetties, a smaller model with four piles and a larger model supported by twenty-four piles. SPSI effects are considered through p-y, τ-z, and q-z springs, the behaviours of which are determined by following commonly employed procedures. The structures’ responses are investigated under the influence of various assumptions regarding the behaviours of springs, as well as steel plasticity. The current investigation underscores the substantial influence of the axial soil–pile interaction on the response of the jetty, particularly in terms of its failure mode. Moreover, it demonstrates the importance of incorporating p-y springs, even though the choice between their linear or nonlinear constitutive behaviour is found to be less critical. Finally, the study concludes that the behaviours of the springs significantly affect the system’s ductility and the degree of steel yielding in the piles, while also highlighting the unconservative influence of neglecting SPSI phenomena.

Computational Simulation of Monopile Scour under Tidal Flow Considering Suspended Energy Dissipation

Local scour around bridge foundations significantly impacts the stability and safety of marine structures. The development of scour holes adjacent to the pile foundations of sea-crossing bridges, influenced by tidal currents, involves multidimensional physical fields, multiscale coupling, and complex variations in marine loads. However, experimental models alone are inadequate for investigating the underlying mechanisms. Numerical simulation, a critical tool for studying local scour processes, faces the challenge of accurately modeling sediment transport, particularly under tidal flow conditions near pile foundations. To solve this challenge, this research considers the effect of reciprocating flow on sediment shear as well as its characteristic dissipation based on the immersed boundary method, introduces a reciprocating flow dissipation mechanism, and adds a momentum exchange term between the fluid and the sediment to derive a new controlling equation; a new tidal flow localized scour solver is ultimately constructed, termed TidalflowFOAM. The solver effectively simulates complex flow conditions under tidal currents, extending the modeling capabilities to more realistic three-dimensional bridge scour scenarios under combined wave and current conditions. Validation through cases reported in the literature and a series of controlled experiments, encompassing varying depths, flow velocities, and pile diameters, demonstrates the solver’s proficiency in capturing post-vortex data and accurately reflecting the influence of key factors on scour depth. However, the fidelity of the simulated scour hole morphology under tidal flow conditions behind the piles requires enhancement. The proposed numerical model for tidal flow conditions has high solution accuracy and can guide practical engineering applications.

Pseudo strain-hardening alkali-activated composites with up to 100 % rubber aggregate: Static mechanical properties analysis and constitutive model development

Strain-hardening alkali-activated materials (SHAAM) provide a sustainable alternative to conventional strain-hardening cementitious composites (SHCC), offering significant environmental and economic benefits. This study examines the effects of various rubber powder (RP) volume replacement ratios (0 %, 25 %, 50 %, 75 %, and 100 %) on the properties of Rubber Powder Modified Strain-Hardening Alkali-Activated Composite Material (R-SHAAM), assessing workability, uniaxial compressive behavior, and uniaxial tensile behavior. The findings reveal that R-SHAAM with 100 % RP aggregate significantly enhances durability, achieving a 50.7 % reduction in crack width. Optimal axial tensile performance is observed at a 25 % replacement ratio, where R-SHAAM shows an 8.1 % increase in tensile strength and a 4.1 % increase in ultimate tensile strain. The robust multi-dimensional performance of R-SHAAM across different RP replacement ratios suggests its potential for diverse applications including pavement, marine structures, and explosive engineering, thereby offering valuable insights into sustainable material design and the effective recycling of waste materials in construction.

Effects of cyclic ageing frequencies on the ageing and mechanical behaviour of adhesive materials: Experimental analysis and numerical study

In marine structures adhesive joint structures are often exposed to cyclic conditioning where the ambient humidity changes cyclically during their service. Though some comprehensive studies on the aging of adhesives exist, these researches mainly focus on monotonic aging conditions where the adhesive joints are exposed to a wet condition continuously for a long time. However, the few investigations performed on the cyclic moisture absorption of adhesive materials show that the parameters obtained in monotonic aging conditions are not suitable for estimation of the aging behaviour of adhesive exposed to alternating humidity. An important question that can arise is whether or not this frequency affects the mechanical behaviour of adhesive joints under cyclic aging condition. In this investigation bulk dogbone and square samples were manufactured, subjected to cyclic aging conditions with four different aging frequencies and tested. The results show that the moisture diffusion constant of adhesives exposed to higher aging frequencies increase more than those exposed to lower aging frequency conditions. In addition, the moisture content only affects the degradation of strength and stiffness of the tested adhesives in different aging frequencies.

Advanced Analysis of Marine Structures

In the analysis and design of marine structures, one of the key issues is the accurate prediction of their strength under various load conditions, particularly impact and ultimate and fatigue strength [...]

Novel numerical approach toward hybrid nanofluid flow subject to Lorentz force and homogenous/heterogeneous chemical reaction across coaxial cylinders

The combination of AA7075 and Ti6Al4V aluminum alloys provides an effective balance of endurance, corrosion resistance, and lightness. Some potential applications include aviation components, marine structures with anti-corrosion characteristics, surgical instruments, and athletic apparel. Therefore, the hybrid nanofluid (Hnf) consists of aluminum alloys (AA7075-Ti6Al4V), water (50%), and ethylene glycol (EG-50%) in the current analysis. The Hnf flow subject to heat radiation and Lorentz force is studied through coaxial cylinders. In addition, the flow has been observed under the impacts of homogeneous-heterogeneous (HH) chemical reaction and exponential heat source/sink. The modeled equations (continuity, momentum, HH, and heat equations) are renovated into the non-dimensional form through the similarity approach, which are further numerically computed by employing the ND-solve technique coupling with the shooting method. It can be noticed from the graphical results that the flow rate of Hnf drops with the rising effect of porosity and magnetic field parameters. The addition of AA7075-Ti6Al4V nanoparticles (NPs) also reduces the fluid temperature and velocity profile. Furthermore, the concentration distribution diminishes with the flourishing effect of HH parameters.

On the role of curvature in the response of air-backed composites to hydrodynamic loading: An experimental study

Composite materials are increasingly utilized in high-performance naval structures, due to their superior properties over traditional materials like steel and aluminum. However, their widespread use is hindered by our limited understanding of their behavior when exposed to marine environments. One of the main loading conditions encountered during operations at sea is the hydrodynamic loading on the side in contact with water. Despite the practical significance of curved composite structures, the state-of-the-art on air-backed composites relies on the study of flat plates. Here, we use three-dimensional digital image correlation and planar particle image velocimetry to study the influence of curvature on the dynamic response of composite plates to hydrodynamic loading. Our findings reveal that curvature significantly influences both structural deformations and flow physics. The curved plate experiences localized vibrations with lower amplitude and higher frequency, caused by its increased stiffness. Additionally, the hydrodynamic pressure at the center of the plate decays faster in time for the curved configuration, highlighting the importance of curvature in shaping fluid–structure interactions. Our results advance the understanding of fluid–structure interactions in composite materials and highlight the importance of curvature in the design of resilient marine structures.

Behavior of circular concrete-filled double-skin aluminum alloy tubular stub columns: Test, modeling and confinement-based design

Concrete-filled double-skin steel tubular members have been widely adopted in marine structures, thereby being constantly subjected to harsh corrosive environment. This has triggered the emergence of concrete-filled double-skin aluminum alloy tubular (CFDAT) members of late, wherein aluminum alloy tube is taken as an excellent corrosion-resistant material. Nevertheless, the design guidelines of CFDAT columns have not yet been incorporated into existing international standards due to the absence of relevant research, hindering their structural applications. To this end, this study aims to further investigate the behavior of circular CFDAT stub columns under concentric loading and to clarify the confinement mechanism of this member. In total, 12 CFDAT stub columns were axially tested and the corresponding experimental results were discussed. The research findings showed that the ultimate load of CFDAT specimens is significantly affected by the hollow ratio, concrete strength and diameter-to-wall thickness ratio of outer tube. Using the test results, finite element (FE) model was developed and then utilized to ascertain the confinement mechanism of CFDAT columns, followed by a comprehensive parametric study of such members. Subsequently, the feasibility of current design formulas for the design of CFDAT columns was evaluated against the experimental results and outputs of FE analysis, accompanied by an obvious prediction deviation. Accordingly, a new confinement coefficient reflecting the confinement effect of concrete strength in such members was suggested, which can reasonably capture the interaction between of aluminum alloy tubes and sandwiched concrete. Using this coefficient, a unified design model for estimating the ultimate load of CFDAT and CFAT members was suggested and has better predictive ability than existing design codes and empirical formulas.

Experimental and numerical analysis of wave forces on a vertical truncated cylinder with different depths of submergence under focused waves

Accurately determining the extreme wave forces acting on marine structures is crucial for ensuring their safety. This study investigates the maximum values and transfer functions of wave forces on a fixed vertical truncated cylinder under focused waves through experimental analysis and numerical simulations. Firstly, an experiment was conducted to examine the influence of the wave steepness kpAp, structural scale D/Lp and depth of submergence S2/d on both the horizontal and the vertical forces exerted on the cylinder. These factors were found to significantly influence the maximum values and transfer functions of the wave forces, particularly those of the vertical force during wave slamming events. To further understand the interactions between the focused waves and the vertical truncated cylinder, a numerical model based on the Reynolds-Averaged Navier-Stokes (RANS) equations in OpenFOAM was employed considering different heights above the surface of static water S1/d and varying depths of submergence S2/d. The validity of this model was confirmed by comparing its results with those of the experiment. Following this, the effects of S1/d and S2/d on the maximum values as well as the transfer functions of wave forces on the cylinder were discussed, including in scenarios involving wave slamming and wave overtopping events. Finally, an empirical formula for calculating the wave force was proposed, taking into account the influence of kpAp, S1/d, and S2/d on the inertial coefficient CM and the coefficient of pressure correction CP. The results demonstrated that this formula can be used to accurately predict the maximum wave forces exerted on the cylinder.

Axial compressive behavior of low-alkalinity seawater sea-sand concrete column reinforced with hydrophobic longitudinal SFCBs and FRP hoops

To address corrosion problem of steel bars and shortage of freshwater and river sand in marine and offshore structures, a novel hydrophobic-modified longitudinal steel-FRP composite bars (SFCB) and FRP hoops reinforced low-alkalinity seawater sea-sand concrete (SWSSC) is developed. However, axial compressive behavior of hybrid SFCB and FRP reinforced columns is not clear and the applicability of existing design methods is low. Here, nine hybrid reinforced columns have been designed and tested. Typical failure modes of columns and axial compressive behavior of constituent materials (i.e., hydrophobic reinforcements and low-alkalinity SWSSC) are investigated. It is found that the synergistic confining effect formed by hybrid reinforcement are significant. The mesh confinement formed by densely distributed FRP hoops and longitudinal SFCBs improves the local buckling behavior, and effectively constrains the lateral expansion of concrete core, resulting in improved compressive strength and ductility of column. The compressive contribution of single longitudinal SFCB to ultimate load capacity of column can be enhanced effectively, up to 36.3 %, by increasing steel content of SFCB. Based on this, a prediction model of hybrid reinforced columns is proposed, which can accurately evaluate the ultimate load capacity. This work provides valuable experimental observations and load capacity model for hybrid reinforced column, which promote its design and application in marine engineering.

Life-cycle performance prediction and interpretation for coastal and marine RC structures: An ensemble learning framework

Long-term exposure to coastal and marine environments accelerates the aging of reinforced concrete (RC) structures, impacting their structural safety and society impact. Traditional assessments of long-term performance deterioration in RC structures involve complex, nonlinear, and time-intensive studies of physical mechanisms. While existing machine learning (ML) methods can assess the lifetime of these structures, they often prioritize data regression over mechanistic interpretation. To enhance the efficiency and interpretability of predicting the life-cycle performance of RC structures, this study introduces a generic framework based on interpretable ensemble learning (EL) methods. The framework predicts life-cycle performance efficiently and accurately, with optimal hyperparameters automatically tuned through Bayesian optimization. Interpretability algorithms clarify the influence of environmental, durability, and mechanical parameters on structural durability and mechanical predictions. Validation employs real-world cases of RC hollow beams in the coastal area of the Guangdong-Hong Kong-Macao Greater Bay Area (GBA). The comprehensive model for RC structures integrates actual data on temperature, humidity, and surface chloride content in the GBA, considering diffusion, convection, and binding effects of chloride ions, corrosion non-uniformity, and crack impact on durability estimation. Comparative analysis with existing ML methods underscores the effectiveness of the framework. The findings highlight the dynamic evolution of feature importance rankings throughout the service life, shedding light on the continuous changes in the significance of different factors when predicting mechanical resistance.

A Novel Method for Estimating the Undrained Shear Strength of Marine Soil Based on CPTU Tests

The undrained shear strength is an essential parameter in the foundation design of marine structures. Due to the complex marine environment and technical limitations, it is difficult and costly to obtain offshore samples. Piezocone penetration tests (CPTU) are relatively low-cost compared to drilling and sampling methods. Therefore, based on the soil behavior type index (Ic) derived from CPTU results, a model for estimating cone factors (Nkt, Nke) is proposed to improve the accuracy of estimation of undrained shear strength. The result shows that the soil behavior type index (Ic) and cone factors take on a negatively correlated exponential relation. Incorporating a cone factor that varies with the soil behavior type index (Ic) significantly enhances the accuracy of undrained shear strength predictions compared to the conventional method of using a constant cone factor. This approach reduces the root mean square error (RMSE) for Nkt (Nke) from 0.124 (0.126) MPa to 0.056 (0.06) MPa, and the mean absolute error (MAE) from 0.0154 (0.016) MPa to 0.0032 (0.0036) MPa. The method was validated at an additional location and the predictions were in high agreement with the results of the consolidated quick direct shear test. The developed method can serve as an effective tool used in the design of foundations of marine structures.

Biofouling sponges as natural eDNA samplers for marine vertebrate biodiversity monitoring

Environmental DNA (eDNA) analysis has now become a core approach in marine biodiversity research, which typically involves the collection of water or sediment samples. Yet, recently, filter-feeding organisms have received much attention for their potential role as natural eDNA samplers. While the indiscriminate use of living organisms as ‘sampling tools’ might in some cases raise conservation concerns, there are instances in which highly abundant sessile organisms may become a nuisance as biofouling on artificial marine structures. Here we demonstrate how a sea sponge species that colonizes the moorings of the world's largest curtain of hydroacoustic receivers can become a powerful natural collector of fish biodiversity information. By sequencing eDNA extracted from Vazella pourtalesii retrieved from moorings during routine biofouling maintenance, we detected 23 species of marine fish and mammals, compared to 19 and 15 species revealed by surface and bottom water eDNA respectively, and 28 species captured by groundfish survey in the surrounding area, which are more ecologically impactful and involve higher additional costs. Sponge-based species inventories proved at least as informative as those obtained by traditional survey methods, and are also able to detect seasonal differences in fish assemblages. We conclude that opportunistic sampling of marine sponge biofouling may become an efficient way to document and monitor biodiversity in our rapidly changing oceans.