A machine learning-based strategy for predicting the mechanical strength of coral reef limestone using X-ray computed tomography

Different sedimentary zones in coral reefs lead to significant anisotropy in the pore structure of coral reef limestone(CRL),making it difficult to study mechanical behaviors.With X-ray computed tomography(CT),112 CRL samples were utilized for training the support vector machine(SVM)-,random forest(RF)-,and back propagation neural network(BPNN)-based models,respectively.Simultaneously,the machine learning model was embedded into genetic algorithm(GA)for parameter optimization to effectively predict uniaxial compressive strength(UCS)of CRL.Results indicate that the BPNN model with five hidden layers presents the best training effect in the data set of CRL.The SVM-based model shows a tendency to overfitting in the training set and poor generalization ability in the testing set.The RF-based model is suitable for training CRL samples with large data.Analysis of Pearson correlation coefficient matrix and the percentage increment method of performance metrics shows that the dry density,pore structure,and porosity of CRL are strongly correlated to UCS.However,the P-wave velocity is almost uncorrelated to the UCS,which is significantly distinct from the law for homogenous geomaterials.In addition,the pore tensor proposed in this paper can effectively reflect the pore structure of coral framework limestone(CFL)and coral boulder limestone(CBL),realizing the quantitative characterization of the heterogeneity and anisotropy of pore.The pore tensor provides a feasible idea to establish the relationship between pore structure and mechanical behavior of CRL.

Coral reef ecological pump for gathering and retaining nutrients and exporting carbon:a review and perspectives

How coral reefs with high productivity and biodiversity can flourish in oligotrophic tropical oceans has inspired substantial research on coral reef ecosystems.Increasing evidence shows that similar to water in an oasis in the desert,there are stable nutrient supplies to coral reefs in oligotrophic oceans.Here,with emphasis on the fluxes of organic matter,we summarize at the ecosystem level(1)the multiple input pathways of external nutrients,(2)the storage of nutrients in reef organisms,(3)the efficient retaining and recycling of dissolved and particulate organic matter within coral reef ecosystems,(4)the distinctly high phytoplankton productivity and biomass inside and near oceanic coral reefs,and(5)the export of reef-related organic carbon to adjacent open oceans.These properties enable coral reefs to function as ecological“pumps”for gathering nutrients across ecosystems and space,retaining and recycling nutrients within the ecosystem,supporting high phytoplankton productivity,and exporting organic carbon to adjacent open oceans.Particularly,the high phytoplankton productivity and biomass make waters around coral reefs potential hotspots of carbon export to ocean depths via the biological pump.We demonstrate that organic carbon influx is vital for coral reef ecosystems’carbon budget and carbon export.The concept of the coral reef ecological pump provides a framework to improve the understanding of the functioning of the coral reef ecosystem and its responses to disturbance.Prospects of the coral reef ecological pump in coral reef studies are discussed in changing oceans driven by human activities and global change in the Anthropocene.

Stressed Coral Reef Identification Using Deep Learning CNN Techniques

Deep learning is a machine learning technique that allows the computer to process things that occur naturally to humans.Today,deep learning techniques are commonly used in computer vision to classify images and videos.As a result,for challenging computer vision problems,deep learning provides state of the art solutions to it.Coral reefs are an essential resource of the earth.A new study finds the planet has lost half of its coral reefs since 1950.It is necessary to restore and prevent damage to coral reefs as they play an important role in maintaining a balance in the marine ecosystem.This proposed work helps to prevent the corals from bleaching and restore them to a healthy condition by identifying the root cause of the threats.In the proposed work,using deep learning CNN techniques,the images are classified into Healthy and Stressed coral reefs.Stressed coral reefs are an intermediate state of coral reef between healthy and bleached coral reefs.The pre-trained models Resnet50 and Inception V3 are used in this study to classify the images.Also,a proposed CNN model is built and tested for the same.The results of Inception V3 and Resnet50 are improved to 70%and 55%by tuning the hypermeters such as dropouts and batch normalisation.Similarly,the proposed model is tuned as required and obtains a maximum of up to 90%accuracy.With large datasets,the optimum amount of neural networks and tuning it as required brings higher accuracy than other methods.

Coral Reef and High Sea Level at Luhuitou, Hainan Island during the Holocene

According to the field survey and ^14C dating at Luhuitou, southern Hainan Island, a subsiding area, the authors conclude the high sea level history recorded by coral reef in the Holocene. At least 4 sea level high-stands can be identified from the distribution of coral reef ages： 7300 - 6000 cal.aBP, 4800 - 4700 cal.aBP, 4300 - 4200 cal.aBP and 3100 - 2900 cal.aBP. The highest sea level occurred around 7300 - 6700 cal.aBP, and biological-morphological zones took their shape during the stage. The later coral reefs developed in ponds, depressions, and developed outwards on both sides of Luhuitou peninsula. The modern coral reefs are developing in out reef flat and reef-front slope. Moreover, the time of high sea levels in the northern South China Sea recorded by coral reefs in the Luhuitou peninsula can link up with that in other parts of South China Sea. That means the high sea levels in the South China Sea during the Holocene, which are relative to the warming climate, have the global background.

Methanation of syngas over coral reef-like Ni/Al_2O_3 catalysts

Coral reef-like Ni/Al2O3 catalysts were prepared by co-precipitation of nickel acetate and aluminium nitrate with sodium carbonate aqueous solution in the medium of ethylene glycolye.Methanation of syngas was carried out over coral reef-like Ni/Al2O3 catalysts in a continuous flow type fixed-bed reactor.The structure and properties of the fresh and used catalysts were studied by SEM,N2 adsorption-desorption,XRD,H2-TPR,O2-TPO,TG and ICP-AES techniques.The results showed that the coral reef-like Ni/Al2O3 catalysts exhibited better activity than the conventional Ni/Al2O3-H2O catalysts.The activities of coral reef-like catalysts were in the order of Ni/Al2O3-673Ni/Al2O3-573Ni/Al2O3- 473Ni/Al2O3-773.Ni/Al2O3-673-EG catalyst showed not only good activity and improved stability but also superior resistance to carbon deposition,sintering,and Ni loss.Under the reaction conditions of CO/H2（molar ratio）=1：3,593 K,atmospheric pressure and a GHSV of 2500 h-1,CH4 selectivity was 84.7%,and the CO conversion reached 98.2%.

Numerical Simulation for Shallow Strata Stability of Coral Reef in the Southwest of Yongshu Reef(South China Sea)

In recent years, infrastructure construction on coral reefs has been increasingly developed. Therefore, the shallow strata stability of coral reefs in the South China Sea should be evaluated. This study aims to investigate the profiles for the shallow strata of coral reefs in the southwest of the Yongshu Reef, particularly in the hydrodynamic marine environment, and to establish a geological model for numerical simulation using Geo-Studio. The shallow strata of the coral reefs include mass gravel, sand gravel, mid-coarse sand, silty sand, fine sand, and reef limestone. The shallow reef slope near the lagoon is similar to a ‘layer cake', in which the side close to the sea is analogous to a ‘block cake'. The simulation results showed that coral reef stability depends on wave loads and earthquake strength and on the physical properties of coral reefs. The factor of safety for the outer reef is greater than 10.0 under static, wave, and seismic conditions; this indicated that the outer reefs were less affected by waves and earthquakes. However, the factor of safety next to the lagoon varied from 0.1 to 5.3. The variation was primarily caused by the thick strata of coral reefs close to the sea(reef limestone, typically with the thickness > 10 m and equivalent to a block). The soil and rock layers in the coral reef strata with thicknesses < 10 m showed weak engineering geological characteristics. Our findings can provide useful information to future construction projects on coral reefs.

Mechanical Properties and Microstructure of Portland Cement Concrete Prepared with Coral Reef Sand

The feasibility of using coral reef sand（CRS） in Portland cement concrete is investigated by testing the mechanical property and microstructure of concrete. The composition, structure and properties of the CRS are analyzed. Mechanical properties and microstructure of concrete with CRS are studied and compared to concrete with natural river sand. The relationship between the microstructure and performance of CRS concrete is established. The CRS has a porous surface with high water intake capacity, which contributes to the mechanical properties of concrete. The interfacial transition zone between the cement paste and CRS is densified compared to normal concrete with river sand. Hydration products form in the pore space of CRS and interlock with the matrix of cement paste, which increases the strength. The total porosity of concrete prepared with CRS is higher than that with natural sand. The main difference in pore size distribution is the fraction of fine pores in the range of 100 nm.

Regional hard coral distribution within geomorphic and reef flat ecological zones determined by satellite imagery of the Xisha Islands,South China Sea

Coral reefs in the Xisha Islands （also known as the Paracel Islands in English）, South China Sea, have experienced dramatic declines in coral cover. However, the current regional scale hard coral distribution of geomorphic and ecological zones, essential for reefs management in the context of global warming and ocean acidification, is not well documented. We analyzed data from field surveys, Landsat-8 and GF-1 images to map the distribution of hard coral within geomorphic zones and reef fiat ecological zones. In situ surveys conducted in June 2014 on nine reefs provided a complete picture of reef status with regard to live coral diversity, evenness of coral cover and reef health （live versus dead cover） for the Xisha Islands. Mean coral cover was 12.5% in 2014 and damaged reefs seemed to show signs of recovery. Coral cover in sheltered habitats such as lagoon patch reefs and biotic dense zones of reef flats was higher, but there were large regional differences and low diversity. In contrast, the more exposed reef slopes had high coral diversity, along with high and more equal distributions of coral cover. Mean hard coral cover of other zones was 〈10%. The total Xisha reef system was estimated to cover 1 060 km2, and the emergent reefs covered -787 km2. Hard corals of emergent reefs were considered to cover 97 km2. The biotic dense zone of the reef flat was a very common zone on all simple atolls, especially the broader northern reef flats. The total cover of live and dead coral can reach above 70% in this zone, showing an equilibrium between live and dead coral as opposed to coral and algae. This information regarding the spatial distribution of hard coral can support and inform the management of Xisha reef ecosystems.

A Comparative Study of Numerical Models for Wave Propagation and Setup on Steep Coral Reefs

Complex factors including steep slopes, intense wave breaking, large bottom friction and remarkable wave setup should be considered while studying wave propagation over coral reefs, and how to simulate wave propagation and setup on coral reefs efficiently has become a primary focus. Several wave models can be used on coral reefs as have been published, but further testing and comparison of the reliability and applicability of these models are needed. A comparative study of four numerical wave models (i.e., FUNWAVE-TVD, Coulwave, NHWAVE and ZZL18) is carried out in this paper. These models’ governing equations and numerical methods are compared and analyzed firstly to obtain their differences and connections;then the simulation effects of the four wave models are tested in four representative laboratory experiments. The results show that all four models can reasonably predict the spectrum transformation. Coulwave, NHWAVE and ZZL18 can predict the wave height variation more accurately;Coulwave and FUNWAVE-TVD tend to underestimate wave setup on the reef top induced by spilling breaker, while NHWAVE and ZZL18 can predict wave setup relatively accurately for all types of breakers;NHWAVE and ZZL18 can predict wave reflection by steep reef slope more accurately. This study can provide evidence for choosing suitable models for practical engineering or establishing new models.

Connectivity of fish assemblages along the mangrove-seagrasscoral reef continuum in Wenchang, China

Understanding the connectivity of fish among different typical habitats is important for conducting ecosystembased management, particularly when designing marine protected areas(MPA) or setting MPA networks. To clarify of connectivity among mangrove, seagrass beds, and coral reef habitats in Wenchang, Hainan Province,China, the fish community structure was studied in wet and dry seasons of 2018. Gill nets were placed across the three habitat types, and the number of species, individuals, and body size of individual fish were recorded. In total, 3 815 individuals belonging to 154 species of 57 families were collected. The highest number of individuals and species was documented in mangroves(117 species, 2 623 individuals), followed by coral reefs(61 species,438 individuals) and seagrass beds(46 species, 754 individuals). The similarity tests revealed highly significant differences among the three habitats. Approximately 23.4% species used two habitats and 11.0% species used three habitats. A significant difference(p<0.05) in habitat use among eight species(Mugil cephalus, Gerres oblongus, Siganus fuscescens, Terapon jarbua, Sillago maculata, Upeneus tragula, Lutjanus russellii, and Monacanthus chinensis) was detected, with a clear ontogenetic shift in habitat use from mangrove or seagrass beds to coral reefs. The similarity indices suggested that fish assemblages can be divided into three large groups namely coral, seagrass, and mangrove habitat types. This study demonstrated that connectivity exists between mangrove–seagrass–coral reef continuum in Wenchang area;therefore, we recommend that fish connectivity should be considered when designing MPAs or MPA network where possible.

Remote sensing composite information's trend surface analysis of Nansha Islands coral islets and reefs' top

Based on the remote sensing information feature of Nansha coral islets and reefs that controlled by the Nansha Islands local area's goological structure and growth law, by means of mathematical model and PC, the Nansha Islands coral islets and reefs' top geological data' spatial distribution and local change trend are simulated by using the trend surface system on the remote sensing composite information, and an scientific interpretation and local comparison of Nansha coral islands and islets' spatial distribution feature are made.

Analysis on coral reefs mapping using SPOT5 data at the Dongsha Atoll

Coral reefs are an sensitive-to-environment complex marine ecosystem. The ecosystem of corals is rich in biodiversity. Remote sensing offers a powerful tool for categorizing coral reefs and is the most cost - effective approach for the large - scale reef survey. The Dongsha Atoll, more than 300 km2 with an average depth of 10 m, is located at the northern continental margin of the South China Sea. It has been abused by destructive fishing during recent decades. Three satellite imageries （Quickbird2, ETM ＋ and SPOTS） are used to evaluate the capabilities of SPOT5 imagery to provide data that are useful for categorizing the current distribution of coral reefs therein. During the data processing, unsupervised classification functions are adopted for ETM ＋ and SPOT5 data, while the supervised classification method is used for Quickbird2. The classes are （or not） merged into coral reef, and then will be operated by vectorization, simplification, and topological analysis. There are 1 331 coral reefs larger than 100 m2 with a detection limit of 3 × 3 pixels at the multi - band data of Quickbird2, which is taken as the comparison baseline. The results extracted from SPOT5 and ETM images are less in number and area than those from the Quickbird2 image, whereas the results from SPOT5 data are better than those of ETM data at the silty lagoon due to its higher resolution. SPOT5 XS band 2 fails to distinguish the deep substrate inside the atoll compared with ETM data because of its poor penetration capability. Only SPOT XS band 1 cannot be used to differentiate coral reef from sand bottom. Merging the SPOT5 multi - bands data with the spatial resolution of SPOT5 pan - data and referring to ETM imagery are expected to provide an optimal satellite - based approach for mapping of coral reefs.

The research on the remote sensing＇s information tree model of the Nansha coral islets and reef＇s spatial structure

Based on the Nansha coral islets and reef's time-space attributes,and the intension and extension of the remote sensing information, the concept model and concept system of coral islets and reef are proposed.Then twin-tree remote sensing information model for different kinds of reef is constructed by using abstracted islets and reef's primitive, and the structure recognition system for coral islets and reef type is developed.

Spatial and Temporal Variability of Thermal Stress to China's Coral Reefs in South China Sea

Coral bleaching, caused by elevated sea surface temperature(SST), is occurring more frequently and seriously worldwide. Due to the lack of field observations, we understand little about the large-scale variability of thermal stress in the South China Sea(SCS) and its effect on China's coral reefs. This paper used 4-km high resolution gap-filled SST(Filled SST) data and thermal stress data related to coral bleaching derived from Coral Reef Temperature Anomaly Database(Co RTAD) to quantify the spatial and temporal characteristics of chronic thermal stress and acute thermal stress to China's coral reefs in SCS from 1982 to 2009. We analyzed the trend of SST in summer and the thermal stress frequency, intensity and duration during this period. The results indicate that, as a chronic thermal stress, summer mean SST in SCS shows an average upward trend of 0.2℃/decade and the spatial pattern is heterogeneous. Waters of Xisha Islands and Dongsha Islands of the northern SCS are warming faster through time compared to Zhongsha Islands and Nansha Islands sea areas of the southern SCS. High frequency bleaching related thermal stress events for these reefs are seen in the area to the northwest of Luzon Island. Severe anomaly thermal stress events are more likely to occur during the subsequent year of the El Nino year for these coral reefs. Besides, the duration of thermal stress varies considerably by anomaly year and by region.

Abundance,Diversity and Functional Potentials of Planktonic Bacteria and Microeukaryotes in the Coral-Reef System of Xisha Islands,China

Corals influence microorganisms within the surrounding seawater,yet the diversities and functions of seawater bacteria and microeukaryotes in coral-reef systems have not been well addressed.We collected 40 seawater samples in outer coral reef flats and semi-closed inner lagoons from the surface,middle and bottom layers in the pristine coral-reef system of Xisha Islands,South China Sea.We detected the abundance,composition and distribution of bacteria and microeukaryotes using flow cytometry,qPCR and high throughput sequencing techniques,and profiled the potential ecological roles based on the information of 16S and 18S rDNA sequencing.In terms of flow cytometry,Prochlorococcus dominated the autotrophs with cell abundance ranging from 5.8×10^(2)to 5.44×10^(3)cells mL−1 seawater.Based on qPCR,the 16S rDNA copies were much higher in coral reef flats than in lagoons(P=0.003).The bacterial communities held significantly lower diversity in bottom waters compared with surface and middle waters(P<0.05),which were dominated by SAR11,Flavobacteriales,and Synechococcus.Alveolata represented most of the microeukaryotic communities with Dinophyceae and Syndiniales well represented in all samples.Neither bacterial nor microeukaryotic community exhibited distinct layer or niche pattern,however,Haptophyta and Picozoa decreased with depth and SAR 86,MAST-3 and Picozoa were enriched in lagoons(P<0.05).To adapt the nutrient-poor and organic matter-rich environment,bacterial nitrogen fixation and assimilatory/dissimilatory nitrate reduction were active in the system,and mixotrophy was the most important trophic strategy among microeukaryotes.The study highlighted the ecological adaptability of seawater microbes to the unique coral-reef environments.

Variational Solution of Coral Reef Stability Due to Horizontal Wave Loading

This paper proposes a theoretical method that can be used in calculating the stability of coral reefs or artificial islands.In this work,we employ the variational limiting equilibrium procedure to theoretically determine the slope stability of coral reefs covered with hard reef shells as a result of horizontal wave loads.A reasonable functional is proposed and its extremum is calculated based on the conservation of energy.Then,we deduce the stability factor Ns of coral reefs under combined vertical self-gravity and horizontal wave loads,which is consistent with the published results.We compare some classic examples of homogeneous slopes without hard shells in order to analyze the accuracy of results generated by this variational procedure.The variational results are accurate and reliable according to the results of a series of detailed calculations and comparisons.Simultaneously,some other influence parameters on the reef stability,including the top-layer tensile strength of coral reef,the amplitude of wave loading,and the tensile crack,are calculated and discussed in detail.The analysis results reveal that the existence of a hard reef shell could enhance the stability of reef slope and that there is a nonlinear relationship between the stability factor Ns,the shear strength,and the thickness Ds of the covered coral reef shell.Furthermore,the emergence of top-layer tensile cracks on the coral reefs reduces their stability,and the action of horizontal wave loads greatly decreases the stability of coral reefs.Thus,the hard shell strength and its thickness Ds,surface tensile crack,and wave loading require more careful attention in the field of practical engineering.

Simulation of global ocean acidification and chemical habitats of shallow-and cold-water coral reefs

Using the UVic Earth System Model, this study simulated the change of seawater chemistry and analyzed the chemical habitat surrounding shallow- and cold-water coral reefs from the year 1800 to 2300 employing RCP2.6, RCP4.5, RCP6.0, and RCP8.5 scenarios. The model results showed that the global ocean will continue to absorb atmospheric CO2. Global mean surface ocean temperature will rise 1.1-2.8 K at the end of the 21st century across RCP scenarios. Meanwhile, the global mean surface ocean pH will drop 0.14--0.42 and the ocean surface mean con- centration of carbonate will decrease 20%--51% across the RCP scenarios. The saturated state of sea water with respect to calcite carbonate minerals （t2） will decrease rapidly. During the pre-industrial period, 99% of the shallow-water coral reefs were surrounded by seawater with t2 〉 3.5 and 87% of the deep-sea coral reefs were surrounded by seawater with aragonite supersaturation. Within the 21st century, except for the high mitigation scenario of RCP2.6, almost none shallow-water coral reefs will be surrounded by seawater with g2 〉 3.5. Under the intensive emission scenario of RCP8.5, by the year 2100, the aragonite saturation horizon will rise to 308 m under the sea surface from 1138 m at the pre- industrial period, thus 73% of the cold-water coral reefs will be surrounded by seawater with aragonite undersaturation. By the year 2300, only 5% of the cold-water coral reefs will be surrounded by seawater with aragonite supersaturation.

Dynamic simulation of tropical coral reef ecosystem being disturbed by multiple situations

In consideration of the rapid degradation of coral reef ecosystems, the establishment of models is helpful to comprehend the degradation mechanism of coral reef ecosystems and predict the development process of coral reef communities. According to the characteristics of complex ecosystem of tropical coral reefs in China, the coral reef functional group is the core level variable;combined with the multiple feedback effects of coral reef functional groups and environmental changes, the study presents a coral reef ecosystem dynamics model with hermatypic corals as the core. Based on the simulation of the assumed initial value and the internal feedback of the system, the results show that in the basic simulation(relative health conditions), the coverage area of live corals and coral reefs generally decreased first and then increased, and increased by 4.67% and 6.38% between2010 and 2050, respectively. Based on the calibration model and the current situation of the studied area, the multi-factor disturbance effects of coral reef communities were simulated and explored by setting up three scenarios involving fishing policy, terrestrial deposition, and inorganic nitrogen emissions. Among them, in the single factor disturbance, the fishing policy exerts the most direct impact on the community decline;and the succession phenomenon is obvious;the terrestrial sedimentation has a faster and more integrated effect on the community decline;the effect of inorganic nitrogen emission on the community decline is relatively slow. In the double/multi-factor disturbance, the superimposed disturbance will aggravate the multi-source feedback effect of the coral reef communities development, accelerate the community decay rate, and make its development trajectory more complicated and diverse. This method provides a scientific and feasible method for simulating the damage of long-term coral reef community and exploring the development law and adaptive management of coral reef ecosystems. In the future, it can be further studied in the ecological restoration process and decisionmaking direction of coral reefs.

Spatio-temporal Variations of Sea Surface Wind in Coral Reef Regions over the South China Sea from 1988 to 2017

The seasonal and interannual variabilities of sea surface wind(SSW)in the South China Sea(SCS),especially in coral reef regions such as Nansha Islands,Xisha Islands,Zhongsha Islands and Dongsha Islands were investigated in detail using the Blended Sea Winds dataset(1988-2017).Annual and monthly variations of SSW and sea surface temperature(SST)in the four zones were investigated.Empirical Orthogonal Function(EOF)analysis of wind field was performed to aid in better understanding the different spatial patterns.The results indicate that,as observed in the spatial distribution of the first mode of monthly mean wind speed anomaly,the mag-nitudes in the four island zones are all negative and are similar to each other,showing that the variations of SSW in the four island zones are consistent.In the second mode,the magnitudes in Nansha Islands are opposite to those in the other three zones.The spatial distribution of the third mode reflects regional differences.The maximum annual SSW appears in Dongsha Islands,and the minimum appears in Nansha Islands.The interannual variations of SSW in all island zones are basically concurrent.The island zones with high SSW mostly have low SST,and vice versa.There may be an inverse relationship between SSW and SST in coral reef regions in the SCS.The multiyear monthly variations of SSW in the island zones present a'W'-shaped structural variation.Each island undergoes two months of minimum SSW every year,one during March-May(MAM)and the other during September-November(SON).Both months are in mon-soon transition periods.During the months with low SSW,high SST appears.The SST peaks almost correspond to the SSW troughs.This further indicates that SSW and SST may have opposite changes in coral reef regions.Coral bleaching events often correspond to years of high SST and low SSW.

Wave Attenuation and Friction Coefficient on the Coral-Reef Flat

Several sets of S4 direction-wave-current-tide meters have been deployed on the coral-reef flat of Yongshu Reef in the sea area of Nansha Islands.Based on the observational sea wave data, the attenuation characteristics of the waves propagating on the coral reef flat, the bottom friction coefficients and the transfer of wave energy are discussed in the paper. The results show that, in the relative depths of 0.0613～0.0867, the wave height attenuation per unit distance of wave propagation is 22.09%～46.56%, with an average of 31.35%; the wave energy attenuation coefficient, 33.74%～53.22%, with an average of 43.61%. The average of the bottom friction coefficients on the coral-reef flat is 0.1346, which is about 10 times that on the sand or silt bottom. In the course of propagation on the reef flat, the waves sustain more loss in high frequency than in low frequency and the spectral energy transfers to the low frequency. These results may be used for reference in island and reef engineering.