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(a) Location of the island of Niuatoputapu in the far north of the Lau Archipelago–Kingdom of Tonga. (b) True-color WorldView-2 satellite image of Niuatoputapu. (c) Digital terrain model derived from the image shown in panel b. (d ) Object-based classification of 18 ecologically meaningful seabed classes defined via interrogation of the image shown in panel b and examination of an exhaustive suite of ground-truth information collected in the field. Maps adapted with permission from the Khaled bin Sultan Living Oceans Foundation Global Reef Expedition.
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Carbonate precipitation has been a common life strategy for marine organisms for 3.7 billion years, as, therefore, has their construction of reefs. As favored by modern corals, reef-forming organisms have typically adopted a niche in warm, shallow, well-lit, tropical marine waters, where they are capable of building vast carbonate edifices. Because...
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Citations
... Consequently, new methods have evolved that use satellite data to generate bathymetric charts [12,13]. Land-viewing sensors might not always have excellent spatial resolution when it comes to oceanic pixels located near shorelines whereas land-viewing sensors may not have great rates in terms of time leading to fewer number of satellite images which are cloud-free although this may particularly occur more often in areas such as rainy coastal tropics where cloudiness is frequent and high [7]. Moreover, bathymetric algorithms based on satellite telemetry, often draw on field data calibration [8,9,11,16,17] or a large number of calculations aimed at physically modeling general properties of the water column [10,12,13,14,15,18,19], and are frequently restricted to a single scene portrayed in either multispectral or hyperspectral images taken by space orbiters. ...
Many coastal areas, especially in developing countries or those with limited marine activity, lack detailed depth measurements. Past data in these areas may be incomplete or outdated, making it difficult to create accurate seafloor maps. This is important for the preliminary design of coastal structures. This study aims to explore the best way to use satellite images and open-source software to create Satellite-Derived Bathymetry (SDB) models. Our approach uses three machine learning algorithms (KNN, RF, MLR) to analyze satellite images of different areas. The images come from open-source databases. We use the closest truth data to the targeted area to train the algorithms to predict the unseen data. Our research shows that using satellite data to measure water depth can accurately determine depths of up to 27 meters. Furthermore, our assessment reveals mean absolute errors averaging 0.72 meters and root mean square errors averaging 1.0 meter, with accuracies around 94.6% for both samples. Random Forest (RF) performed better than KNN and MLR. In Sample El-Dabaa, RF performed well with Landsat-08 Single Scene image. The area has rocky cliffs with seagrass, steep slopes, and strong wave movement. In Sample El-Arish, RF's best results came with single scene image from Landsat-08. This area has sandy soil, gentle slopes, and gentle wave movement. Generally, usage of Single Scene image or Median Value image with ML algorithm depends on the seafloor dynamics.
... Satellite imagery presents a distinct advantage in terms of wide coverage area and the ability to capture data on a regular basis [337]. This capability enables long-term monitoring without the need for an onsite presence. ...
... This is also true for machine-learning methods and image processing. Finally, substantive reviews of work related to coral mapping are only available to 2017 [170], [337]. For these reasons, we decided to narrow our analysis to papers published since 2018. ...
The ongoing crisis of climate change necessitates the development of effective methods for monitoring and mapping environmental features and species to ensure their preservation. This thesis explores the application of machine learning algorithms to efficiently map coral reefs using multispectral satellite images. The Maupiti lagoon in French Polynesia serves as a case study. The research led to the production of an automated tool capable of generating coral reef maps from satellite images. Moreover, the tool can be adapted to map other ecosystems, such as forests or ice sheets, provided that the model is retrained with relevant data.
To begin, a comprehensive literature review investigates current methods and trends in utilizing machine learning algorithms for coral reef mapping. Then, the attempts to develop the tool led us to face the special case of compositional data, which are data carrying relative information and lying in a mathematical space known as simplex. Adaptations of conventional methods are required to address the specific characteristics of this space.
First, in response to data imbalance, an oversampling technique is developed specifically for compositional data. Additionally, a spatial autoregressive model based on the Dirichlet distribution is formulated to account for spatial effects that may arise in the mapping process.
Finally, we present the implementation of our final mapping tool. To achieve the desired objective, a two-staged classification process is implemented, combining pixel-based and object-based approaches. This technique enables the tool to achieve an accuracy exceeding 85% with 15 classes.
The research contributes novel solutions for handling compositional data and delivers a high-performing mapping tool for coral reef ecosystems, aiding in environmental management and conservation efforts.
... These technologies provide valuable information on coral reef extent, habitat quality, water quality parameters, and the distribution of key species (Hedley et al., 2016;Obura et al., 2019). Satellite remote sensing offers a broad perspective on coral reef dynamics by capturing data on a global scale (Purkis, 2018). Satellites equipped with sensors capable of detecting changes in sea surface temperature, ocean colour and coral reef structure provide valuable insights into coral bleaching events, algal blooms, and habitat degradation. ...
Amidst escalating threats to coral reefs during the Anthropocene era, an urgent call emerges for a holistic strategy that seamlessly integrates Sustainable Development Goals (SDGs), ensuring the conservation and sustainable development of these vital ecosystems. Employing an interdisciplinary lens, this chapter delves into the current state of coral reefs, shedding light on the critical need for immediate action. The study emphasizes the transformative potential of SDGs as a guiding framework for policies and initiatives aimed at fortifying resilient ecosystems and uplifting the communities intricately tied to coral reef ecosystems. Drawing on diverse case studies and successful conservation models, this chapter discerns key strategies essential for realizing SDGs in the intricate context of coral reefs. The synthesis of ecological and socio-economic perspectives contributes to a nuanced understanding of the multifaceted challenges and opportunities entwined in securing the sustainability of coral reefs within the Anthropocene. The study underscores the imperativeness of collaborative efforts, innovative solutions, and policy coherence to effectively navigate the intricate issues surrounding coral reefs, offering a blueprint for the integration of SDGs into practical conservation and sustainable development initiatives. As coral reefs teeter on the brink of irreversible decline, this research advocates for a comprehensive and dynamic approach that transcends disciplinary boundaries, promoting the vitality of these ecosystems and the well-being of the communities reliant upon them.
... Reviews of methodology can improve efficiency in data collection, making research cheaper, more effective, and, hopefully, more accessible. Of relevance, remote sensing has become a popular method of collecting some data for coral health evaluations due to its accessibility (Hedley et al., 2016;Hochberg, 2011;Knudby et al., 2007;Mumby et al., 2004;Purkis, 2018). However, we did not see this reflected in the review-level literature (e.g. ...
The state of coral reefs has been of great concern, as documented in the growing amount of primary literature. These reports on coral health have accumulated, resulting in reviews of the primary studies (i.e. secondary literature). Recently, such reviews have also accumulated, creating an opportunity to review the secondary literature. Second‐order syntheses (reviews of secondary literature) provide an overview of the field, which can be used to guide future research.
Based on our previously published protocol, we compiled peer‐reviewed secondary literature on coral health from Scopus and Web of Science databases. We synthesised 335 secondary literature papers on coral health, 35 of which underwent critical appraisal and 333 of which also underwent bibliometric analysis.
The secondary literature consisted primarily of qualitative reviews (78%). Over 80% of papers stated informing coral conservation as the review's purpose. Climate change (50%) and coral resilience (42%) were the most studied topics, and bioerosion was the least (3.6%). Critically appraised papers scored poorly on Collaboration for Environmental Evidence Synthesis Assessment Tool criteria (studies did not meet standards 55% of the time). The authors of the secondary literature were highly interconnected (with 30% of the authors having more than 15 coauthors within our dataset) and included authors from countries with coral reefs (predominantly in Australia and USA; 79% of papers). The secondary literature on coral health had a median Altmetric score of 5.27.
We have revealed key gaps in coral health topics for further review (e.g. coral range shifts and microbial biodiversity), particularly when considering conservation policy. Incorporating research in policy could be improved through greater research accessibility and continuing to gather public interest in coral reefs. We further recommend broadening research collaborations to include even more researchers from countries with coral reefs (e.g. Maldives). Finally, the secondary literature on coral health needs better reporting transparency (e.g. publishing code).
Our second‐order synthesis is timely, pushing coral health research in a new direction—one which produces research of higher quality, collaboration, and efficiency. As coral reefs decline, we should also aim to rebuild public trust in research and strengthen the evidence base for conservation.
... Processes such as dispersal, community interactions, and disturbances act together with environmental factors to create spatial signatures on the reef landscape 4 . At the macroscale, spatial dimensions vary from 10 s to 1000 s of meters, defining reef-wide patterns of organization 5 . At the mesoscale (i.e., meters to centimeters) corals often form their own local patterning [6][7][8] . ...
All biology happens in space, and spatial structuring plays an important role in mediating biological processes at all scales from cells to ecosystems. However, the metabolomic structuring of the coral holobiont has yet to be fully explored. Here, we present a method to detect high-quality metabolomic data from individual coral polyps and apply this method to study the patterning of biochemicals across multiple spatial (~1 mm - ~100 m) and organizational scales (polyp to population). The data show a strong signature for individual coral colonies, a weaker signature of branches within colonies, and variation at the polyp level related to the polyps’ location along a branch. Mapping metabolites to either the coral or algal components of the holobiont reveals that polyp-level variation along the length of a branch was largely driven by molecules associated with the cnidarian host as opposed to the algal symbiont, predominantly putative sulfur-containing metabolites. This work yields insights on the spatial structuring of biochemicals in the coral holobiont, which is critical for design, analysis, and interpretation of studies on coral reef biochemistry.
... Penggunaan citra beresolusi spasial rendah meningkatkan level ketidakpastian akan informasi suatu objek pemetaan akibat piksel campuran seperti disepanjang garis pantai . Selain itu, tutupan awan juga menjadi salah satu gangguan dalam interpretasi citra optis (Purkis, 2018;Purkis & Pasterkamp, 2004). Dalam menghasilkan data batimetri yang akurat diperlukan hasil observasi lapangan untuk proses kalibrasi dan validasi (Stumpf et al., 2003) , dan dalam hal ini sangat ditentukan pada kondisi perairan dan kondisi atmosfer wilayah kajian (Hedley et al., 2018;Kerr & Purkis, 2018;Li et al., 2021). ...
Bathymetric maps of shallow waters can aid in managing, monitoring, and protecting ecosystems within them. However, the availability of bathymetric maps for shallow water regions in Indonesia still needs to be improved. Therefore, a method of rapid mapping for bathymetry in shallow waters in Indonesia is needed. This study attempts to apply an automated method for mapping shallow water bathymetry in Tanjung Kelayang using the blue and green bands of the clean-coastal-water mosaic of Sentinel-2 images, chlorophyll-a data from aqua-MODIS, and the Google Earth Engine (GEE) platform. This research aims to test the reliability of the rapid bathymetry mapping method using Sentinel-2 image mosaics, chlorophyll-a data, and band-ratio algorithms on the GEE platform in the study area. The results of the study show that the Satellite Derived Bathymetry (SDB) model has an R2 value of 0,62, a mean absolute error (MAE) of 1,77 meters, and a root mean square error (RMSE) of 2,02 meters, with an estimated optimal depth value of 5 meters and a maximum depth value of 10 meters. Thus, the generated SDB model can be considered a reliable alternative for rapid bathymetry mapping in shallow waters, although it may compromise the accuracy of the resulting bathymetric maps.
... An alternate method of observation to cover large areas is remote sensing-based disease assessments (Kabiri et al. 2013;Maynard et al. 2015), although such methods have their own limitations such as interference via clouds and dust (Purkis 2018). Recently, consumer-grade drones have been increasingly used to monitor coral reef ecosystems (Casella et al. 2017;Kabiri et al. 2020), and this relatively low-cost equipment can clearly increase the ease of monitoring coral reefs (Murfitt et al. 2017). ...
Diseases are a growing global threat to scleractinian corals. This study used a relatively inexpensive commercial drone flown simultaneously along with reef walking/snorkeling to confirm the presence of cyanobacterial Black Band Disease (BBD) on a reef in subtropical Okinawa, Japan. At the surveyed reef, the scleractinian corals included encrusting forms (12.57% ± 5.72 coverage), followed by massive/submassive (6.09% ± 4.05) and tabular corals (2.66% ± 1.19). Our survey is unique in that drone research has not been previously applied to BBD surveys, followed by ground truthing. Thus, this study can be regarded as an example of using drones during coral disease assessments.
... In the absence of extensive empirical data on difficult to measure variables, there is a need to produce reliable spatial proxies and advance spatial analytical approaches which can be used to inform site selection. Indeed, new remote sensing methods are delivering unprecedented performance in high spatial resolution data for shallow coastal seascapes (Hedley et al. 2016;Purkis 2018). These technological advances in remote sensing combined with high-performing predictive modeling techniques provide analytical tools to predict habitat suitability using a combination of spatial proxies for unmeasured ecological patterns and processes (Sekund & Pittman 2017;Schill et al. 2021aSchill et al. , 2021b. ...
Coral reefs are experiencing unprecedented levels of stress from global warming, ocean acidification, fishing, and water pollution. In the Caribbean and Western Atlantic, multiple stressors have resulted in widespread losses of the dominant reef‐building Acroporid corals, two of which are listed as threatened species under the 1973 U.S. Endangered Species Act. In response, active coral reef restoration through the outplanting of live corals has become a widespread intervention technique. To increase restoration success, active coral reef restoration requires significant investment and careful planning, and selection of suitable sites for coral outplanting is an essential early step with considerable influence on restoration outcomes. We applied a maximum entropy model to predict and map habitat suitability for the reef‐building coral species, Acropora palmata , around the island of St. Croix in the U.S. Virgin Islands. Based mostly on bathymetry and benthic habitat type, the highest performing model predicted approximately 21.75 km ² of the highest probability of suitable habitat, of which over half occurred within existing marine protected areas (MPAs). Outplanted coral at 60% of sites coincided with predicted maximum habitat suitability index values greater than 0.75 and 35% with values greater than 0.90. The model reveals that all three statutory MPAs with shallow water coral reefs have a considerable area (13.24 km ² ) of predicted high suitability seabed with potential for active A. palmata restoration efforts. The predictive spatial modeling approach provides a cost‐effective tool to inform future coral restoration design and to evaluate the habitat suitability of coral outplanting sites.
... El mapeo del hábitat es un componente importante para la investigación y gestión de cualquier ecosistema (Kachelries et al., 2014), al representar conocimiento básico que facilita el monitoreo y gestión de estos. Programas de conservación enfocados en zonas marinas se han visto en los últimos años beneficiados por una mayor disponibilidad de mapas de hábitat que caracterizan manglares (Wang et al., 2019), praderas de pastos marinos (Veettil et al., 2020) y arrecifes de coral (Purkis, 2018). ...
Marine protected areas (MPAs) are the main tool for the conservation of coastal and marine ecosystems. However, historically their establishment and design has been driven by ease of implementation and political and socioeconomic concerns. Given the high cost of administrating large areas and small availability of resources, mainly economic, conservation should focus on areas where the efforts invested are efficient to minimize the loss of biodiversity and ecosystem services. In this study, using a systematic approach, we integrated habitat beta-diversity models and seascape metrics for the selection of priority conservation areas in Puerto Morelos Reef National Park (PMRNP). Five habitat classes were recognized from the analysis of quantitative estimates of benthic substrates from 111 sites: 1) seagrass dominated, 2) medium seagrass and sand cover, 3) sand dominated, 4) medium cover to algal dominance over calcareous matrix, and 5) reef crest. The habitat classes were employed to produce a thematic reef benthic habitat map (overall accuracy of 85.16% and a Kappa index of 0.80) using a supervised classification on a PlanetScope high-resolution satellite image from December 2021. The resulting thematic map was used to calculate shape complexity, connectivity, and habitat beta-diversity. The maps obtained were used to perform an iterative weighted overlay analysis, using all possible combinations of weighting values with 10% increments between layers. The resulting 83 layers were then integrated to obtain an optimal map that describes the priority conservation areas of the PNAPM, identifying four priority zones where management activities should be focused. The current zonation in the MPA’s management plan is not consistent with the priority areas identified from the spatially explicit analysis conducted. Therefore, the results obtained can help the managers in this important protected area to improve conservation efforts.
... However, LiDAR is still expensive for large-scale investigations. Similarly, drones with fluid lensing and structure-from-motion (SFM) technologies [50] facilitate centimeter-scale resolution [51] bathymetric mapping. But drone investigations are limited to comparatively small areas due to battery restrictions of quadcopters and fixed-wing remote-controlled aerial vehicles. ...
... The GBM rivers system is the mainstay of lowland water discharge and stability of the lowland biodiversity of the Bengal basin. These initiate in the Himalayas and transmit the expected yearly sediment of ~5 00 million tons to ~1 .4 billion tons [65][66][67]; Fig. 3d], discharge ~1 .5 million m 3 s − 1 during peak periods [68], and have a strong effect on the lowlands through sedimentation, though sedimentation is gradually decreasing in the delta (Fig. 3d) from the upstream due to anthropogenic activities [19,43,51]. In the Indian Green vegetation 1989 726 201 163 565 5118 2000 1271 358 235 811 4096 2014 660 1244 768 2761 1233 2020 397 2415 1457 2256 138 Fig. 7. MNDWI classification results from 1989 to 2020 and trend lines. ...
Waterlogging is one of the major global problems which affects agro-economic activities around
the world. In the coastal areas of Bangladesh, especially the southwestern coast, drainage
congestion and waterlogging are very common which makes the area uninhabitable. Therefore,
timely checking of drainage systems and surface water, and conveying data on the dynamics of
drainages and surface water are important for plan and supervisory processes. The present study
took an effort to illustrate the waterlogging and morphological change of the rivers in the
southwestern coast of Bangladesh through the Modification Normalized Difference Water Index
(MNDWI) values which are valuable indicators for monitoring the water area and land use pattern
change. Landsat images (Landsat L8 Oli TIRS, Landsat ETM+, Landsat TM) were used in the
research. The study reveals that from 1989 to 2020, the shallow water area (mostly covered with
rivers) decreased by ~14.30 km2 yr− 1
, whereas the wet-land area (mostly covered with beels and
water logging areas) increased by ~ 67.12 km2 yr− 1
. The bare land area also increased at a rate of ~ 36.90 km2 yr− 1
. On the other hand, the green vegetation decreased at a rate of ~166.1 km2
yr− 1
, whereas the moderate green vegetation area increased by ~ 69.77 km2 yr− 1 for the same
period. In the coastal zones of Bangladesh, the polders, embankments, upstream dams, etc.,
enhance more sedimentation within the channels rather than in the nearby tidal plains. As a
result, the shallow water area which is mostly covered by rivers is gradually decreasing. Moreover, due to increase in wet-land areas with salinity intrusions which affect the vegetation.
Therefore, the green vegetation area is regularly declining due to demolition or conversion to
moderate green vegetation. The findings of the research will be supportive for coastal scientists
worldwide, policy makers & planners, and finally supportive for sustainable management of the
coastal areas including Bangladesh.
