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    Blind spots in global soil biodiversity and ecosystem function research

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    A comparison of baleen whale density estimates derived from overlapping satellite imagery and a shipborne survey

    Here we tested the capacity of VHR imagery to provide estimates useful for monitoring whale distribution and densities, using a direct comparison with a ship-based line transect survey to gauge the relative sighting rates obtained by the satellite platform in comparison to that of the ship. Our results show that density estimates derived from satellite imagery (0.13 whales per km2, CV = 0.38—taken from calm waters) are approximately 0.39 of those estimated from the ship-based survey (0.33 whales per km2, CV = 0.09); an encouraging result suggesting that data from satellite imagery has potential to detect whales at similar levels to a traditional survey method. These results match our expectation that image derived densities would be lower than that of the ship-survey, with the instantaneous nature of the image acquisition on the satellite platform likely a strong driver of these differences, in addition to limitations in image resolution and the potential for random fluctuations in local whale densities during the time between acquisition of satellite images and the vessel-based survey. However they also demonstrate that satellite surveys have sufficient whale detection capacity that they can provide a complementary approach to monitoring whale presence in remote regions where regular surveys are difficult.
    In setting up this study, we chose an area that (1) is of specific scientific interest in terms of whales; (2) is remote and relatively difficult to access, but has had some whale survey effort; (3) where the environmental conditions are changing; and (4) where whale density and habitat use patterns are required to understand population recovery from exploitation and spatial overlap with the regional fishery for Antarctic krill. We focused on an area where one whale species very strongly predominates (humpback whales) in order that our results have potential use for inference about the density patterns of this species, and as there is a smaller likelihood that species mis-identification would introduce bias. We also chose a sea channel which is relatively sheltered, reducing the likelihood of turbulent sea conditions (particularly wind on sea), which can make satellite images useless for survey. Our site selection considerations highlight the limitations still facing development of VHR as a platform, and we consider these limitations and next steps to address them in the following sections. We propose that this method can be used to investigate spatial and temporal patterns of whale distribution and densities, supplementing existing methods, providing that the limitations of this new method are carefully considered during design and implementation.
    Weather conditions, specifically the sea state, impact detectability of whales at sea. Sea state is known to influence the ability of observers to detect animals, with worsening conditions reducing the detection probability. Consequently, effort is typically halted when conditions exceed a predefined limit. In all at-sea surveys, sea state increases the likelihood that the assumption of perfect detection on the track line will be violated. If detection off the track line is impacted by environmental conditions, inclusion of covariates in the detection function can take account of this bias44 (up to a cut off, normally 5). However, if poor sighting conditions impact detection on the track line, alternative methods such as a double-observer/platform study or a mark recapture approach can be implemented to account for and quantify this bias. For an image-based survey, poorer weather conditions will also reduce the ability of the observer to differentiate FOIs from background noise (i.e. breaking waves, wind lines, etc.)30. This results in fewer features being identified, and lower reported densities. Poor sea state, and associated wind conditions, typically ground aerial surveys, whether manned or UAS-based, or force them to be aborted inflight. Here we show that worsening sea states in the south of the study area on the day that the image was taken (Fig. 2), correspond to lower perceived and estimated densities in these regions. Compared to the northern area, the surface conditions of the southern image were less conducive to the visual detection of FOIs, showing an increased frequency of white-caps and wind lines, possibly because this region is prone to katabatic winds sweeping into the channel. Densities in the south of the survey area, where the sea state was poorer, were 0.4 of those from calmer regions (0.05 versus 0.13 whales per km2, CV = 0.58 and 0.38, respectively, Table 2). To address this effect in the future, an adapted version of a Mark-Recapture Distance Sampling (MRDS) analysis, such as45 using multiple observers to review images33, could be applied to assess variations in detectability as a function of covariates (i.e. sea state), and investigate the impact of perception bias on whale detection. However, to accurately parameterise a multi-covariate model, several tens, if not hundreds of whale detections would be needed. Another approach could be to collect multiple images of the same area very close in time (within several seconds to a minute of each other), to quantify the variation in whale detections according to sea state when variation in true whale density is likely to be negligible. In the present study, density comparisons were made using data from the northern (calmer) portion of the imagery only (0.13 whales per km2, CV = 0.38, Table 2).
    When planning satellite imagery analysis, species composition of the focal area needs to be carefully considered, because at present this approach has very limited capacity to differentiate between species when compared to in situ surveys, due to the resolution of the images (~ 30 cm in this study). Our density estimates most likely reflect the density of humpback whales using the area of the Gerlache Strait in summer, because these are the most commonly sighted species in this region, both in terms of previous surveys, where they comprise  > 80% of sightings15,16, and during the present ship-based survey ( > 95% of the groups were identified as humpback whales). During summer periods, other larger baleen whale species tend to be seen further offshore, exhibiting affinity for the more open waters of the Bransfield Strait15. Smaller cetacean species (e.g. Antarctic minke whales, Balaenoptera bonarensis and both Type A and B killer whales46,47,48, Orcinus orca), co-occur with humpback whales in the Gerlache Strait but are unlikely to be misidentified as humpback whales, either by ship or imagery surveys, because of their differing size, surface behaviours and morphology. Southern right whales Eubalaena australis are occasionally sighted in this region too16. However, head callosities are normally visible in overhead imagery of this species, and offer a clear means of differentiation30,31. Since other species likely reflect at best a very small fraction of the image-survey detections, they are unlikely to comprise a significant component of the overall density estimates.
    Obtaining reliable whale density estimates require adjustments for biases. In addition to perception bias, as mentioned above, another key bias is availability bias45. Availability bias is the underestimation of density that occurs as a result of a proportion of animals being underwater, or too deep in the water for detection by the survey platform as it passes a point in the ocean. In the present study, we applied an estimate of surface availability49 (where availability is 1-availability bias), which was derived by taking dive-recording suction cup tag data from humpback whales in the same region and time, to estimate the proportion of time a whale spends at the surface, versus its dive. Applying this correction, density was initially estimated as 0.12 whales per km2 (CV = 0.38) over the whole region surveyed, and as 0.13 whales per km2 (CV = 0.38) in calmer waters. However, we note that when tag data are processed, the analyst determines the threshold at which the animal transitions from being present at the surface, to when it dives50. Typically, for baleen whales, dives are classified as such when the whale is  > 4–5 m for  > 20 s. However, with such a threshold, shallow dives of  More

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    Surface cooling caused by rare but intense near-inertial wave induced mixing in the tropical Atlantic

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    Physical and mechanical properties of wood and their geographic variations in Larix sibirica trees naturally grown in Mongolia

    Physical and mechanical properties of wood
    The AD (0.62 to 0.68 g/cm3) and OD (0.58 to 0.65 g/cm3) values obtained this study were similar with respect to basic density33 in the same sample trees (Table 2), whereas our results for mean AD values were relatively higher than those for L. sibirica reported by Ishiguri et al.27 and lower than those reported by Koizumi et al.5. Radial variations of AD and OD showed similar patterns to those reported by other researchers of L. sibirica5 and L. kaempferi16. Meanwhile, Cáceres et al.3 reported an influence of extractives on density in L. kaempferi. They found that the hot-water extractive content of L. kaempferi varied between 2.9 to 6.9% among 20 provenances, suggesting that actual wood density might be about 5% lower than AD. As shown in Table 3, cold-water extractive content ranged from 7.3 to 16.1%, and the mean values of EOD (0.54 g/cm3, Table 2) were about 10% lower values compared to OD (0.61 g/cm3, Table 2). These results indicated that the effect of cold- or hot-water extractives on wood density might be greater in L. sibirica compared to other Larix species.
    Ishiguri et al.27 reported that radial shrinkage at 1% moisture content change showed almost constant values from pith to bark, whereas tangential shrinkage increased up to 4 cm from pith and then became constant at around 0.3%. The mean values and radial variation patterns examined in this study for shrinkage in both the radial and tangential directions in L. sibirica were similar to those of L. sibirica examined by Ishiguri et al.27.
    Although the tree ages varied, the mean values of MOE, MOR, and CS of the L. sibirica trees in the present study (Table 4) were similar to those found in a previous study for L. sibirica that grow naturally in Mongolia27 but lower than those for L. sibirica that grow naturally in Russia5 and higher than those for L. kaempferi planted in Japan22,24. The mean SS was higher than that of L. sibirica planted in Finland9 and L. kaempferi planted in Japan24. In the radial variation, similar radial trends were found in L. sibirica that grow naturally in Mongolia27 and in L. kaempferi planted in Japan22.
    Based on the obtained results, the mean values of the physical and mechanical properties of L. sibirica collected from five different provenances in Mongolia are similar to those of L. sibirica and other Larix species found in other countries. Thus, wood resources from L. sibirica harvested in Mongolia can be used for similar purposes to other Larix species, such as construction materials.
    Juvenile and mature wood
    The boundary between juvenile and mature wood ranged from the 17th to 24th annual rings from the pith (Table 6). The results were similar to those reported for L. kaempferi trees17,22,42. However, Ishiguri et al.27 showed that juvenile wood might exist within 4 cm from the pith in L. sibirica. In the present study, the boundary was within 2 to 5 cm from the pith among the provenances, suggesting that juvenile wood formation in L. sibirica trees that grow naturally in Mongolia is not only affected by tree age but also by growing conditions.
    We previously reported that mean values of annual ring width were 1.55, 2.47, 0.49, 1.86, and 1.74 for Khentii, Arkhangai, Zavkhan, Khuvsgul, and Selenge, respectively33. This result indicates that the radial growth rate was extremely slow in Zavkhan compared to other four provenances. Shiokura and Watanabe28 reported that suppressed radial growth in the initial stage of tree growth resulted in prolonging the juvenile wood formation period in Picea jezoensis and Abies sachalinensis. Although significant differences among provenances were also found in annual ring number from the pith in the boundary between juvenile and mature wood (Table 6), the difference in the earliest (17th) and the latest (24th) annual ring number from the pith in the boundary was only 7 years. Thus, the radial growth rate in L. sibirica does not have a strong effect on the cambial age at which the production of mature wood cells begins. However, further research is needed to clarify the relationship between the radial growth rate and annual ring number from the pith in the boundary between juvenile and mature wood in this species.
    As shown in Table 7, significant differences between juvenile and mature wood were found in the mean values of physical properties, tracheid length, and mechanical properties, except for SS: the values of the physical and mechanical properties of juvenile wood were lower than those of mature wood. These lower values can be explained by shorter tracheid length and lower wood density. Similar results were obtained by several researchers of softwood species17,22,24,28,29. For example, Koizumi et al.24 found that, in L. kaempferi, the mean MOE, MOR, CS, and SS values were 8.2 GPa, 93.3 MPa, 54.0 MPa, and 11.5 MPa in juvenile wood and 9.5 GPa, 97.2 MPa, 55.1 MPa, and 11.4 MPa in mature wood, respectively. Bao et al.25 reported that the mechanical properties of juvenile wood were significantly lower than those of mature wood in Larix olgenis and L. kaempferi. We also found lower mechanical properties, basic density, and shorter latewood tracheid length of juvenile wood in 67-year-old L. kaempferi22. Thus, the presence of juvenile wood should be considered when utilizing wood resources of this species as construction materials requiring higher strength properties.
    Correlation among physical and mechanical properties of wood
    Figure 4 shows the correlation coefficients of the physical and mechanical properties of three different wood types (all types of wood, juvenile wood, and mature wood). In general, wood density is positively related to shrinkage in the radial and tangential directions44. The results of this study showed significant correlations between radial shrinkage at 1% moisture content and EOD in mature wood and all wood, suggesting that EOD can predict shrinkage in the radial direction in this species. Wood density is also positively correlated with many types of mechanical properties of wood45,46. CS was positively correlated with all types of wood densities measured in this study. The MOE and MOR in mature wood and all wood only exhibited a significant positive correlation with EOD. These results indicate that MOE and MOR values were correlated with wood substances without extractives, and these values in juvenile wood might be related to other properties, such as microfibril angle. Luostarinen and Heräjärvi10 reported that water-soluble arabinogalactan contents were weakly correlated with SS in L. sibirica. SS was significantly correlated with AD, but not with EOD, suggesting that cold water-soluble extractives, such as arabinogalactan, might be affected on the SS in this species.
    Based on these results, strength properties (e.g., bending properties and compressive strength) can be estimated with each other and predicted by EOD. In addition, SS might be influenced by the presence of cold water-soluble extractives, such as arabinogalactan.
    Among-provenance variations
    Cáceres et al.3 reported that significant among-provenance differences were not found in basic and oven-dry densities, whereas hot-water extractive content was significantly affected by provenances in L. kaempferi. We also previously demonstrated that no significant differences among provenances were found in the basic density of L. sibirica naturally grown in Mongolia33. Although the cold-water extractive content significantly differed among provenances in this study, all examined densities, such as AD, OD, and EOD, showed no significant differences among the five provenances (Tables 2 and 3), indicating that wood density might not vary greatly among provenances. Thus, it can be concluded that genetic variations in relation to wood density might be small in L. sibirica trees naturally grown in Mongolia.
    In half-sib families of P. jezoensis, F-values obtained by an ANOVA test for AD, MOE, and MOR among families gradually decreased from juvenile to mature wood47. In addition, Kumar et al.48 reported that estimates of narrow-sense heritability for MOE were generally higher in the corewood than in the outer wood in Pinus radiata. For Larix species, significant differences in wood density, CS, and SS but not in MOE and MOR were found in outer wood among 23 provenances for 31-year-old L. kaempferi24. Thus, genetic variations in the physical and mechanical properties of juvenile wood were higher than in mature wood in many softwood species. Significant differences were also found in most of the mechanical properties among provenances, except for CS (Table 4). In addition, significant differences were found in all examined physical and mechanical properties except for CS in mature wood among the five provenances, while no differences were found in juvenile wood for many properties (Table 7). Similar results were obtained in estimated MOE and MOR values at the 10th and 30th annual rings from the pith: no significant among-provenance variations were found in MOE and MOR at the 10th annual ring from the pith, but significant differences were found in the 30th annual ring from the pith (Table 5). Although the environmental conditions in the five provenances were not the same, the genetic variations in physical and mechanical properties among provenances were large in mature wood compared to juvenile wood for L. sibirica grown naturally in Mongolia. Further research is needed to clarify the genetic factors of the physical and mechanical properties of wood in L. sibirica.
    Based on the results, there are significant among-provenance differences in the physical and mechanical properties of wood, especially in mature wood, in L. sibirica grown naturally in Mongolia. The physical and mechanical properties of wood in this species, especially in mature wood, can be improved by establishing tree breeding programs: families or clones with higher mechanical properties can be produced to achieve sustainable forestry in Mongolia. More

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    Deep neural network recognition of shallow water corals in the Gulf of Eilat (Aqaba)

    One of the major challenges in the field of contemporary ecology is the documentation of ecosystem change over time. Among coastal marine biota, coral reefs are home to a unique hotspot of biodiversity. In the last decades, coral reefs are undergoing a severe decline worldwide1,2,3 due to a combination of ocean acidification4,5, and seawater warming6,7, their adverse impacts intensified by anthropogenic eutrophication and pollution8. These bring about both the decline in live reef cover and a decrease in coral species diversity1. Hence it is of paramount importance to monitor and document the rates of reef decline and identify the relative importance of stressors in each reef. An additional benefit of automated analysis of reef images is its potential as a tool to evaluate the long-term success of bioremediation projects of damaged coral reefs9 and reef protection measures.
    The use of artificial intelligence (AI) to solve the time-consuming, tedious manual classification of coral species and determination of their abundance in real-time, is a Herculean task by itself due to the immense numbers of necessary images and their examination. Automated Deep learning (DL), a branch of AI, has the potential of solving this problem efficiently, and by far exceeds in terms of reliability and accuracy human reef documentation and monitoring. Like the human brain, the more data the computer learns under the DL mechanism, the better it performs at distinguishing among classes of coral species in the present application.
    The highly-diverse coral reefs of the Gulf of Eilat (Aqaba) are of special scientific interest not only for being the most Northern reefs, but for benefiting the economy of neighboring communities in both Israel and Jordan. Although highly-diverse10, these reefs have suffered from a sequence of disasters, including a rare low tide in 197011, the recovery from which was impeded by repeated oil pollution following the closure of the Suez Canal between 1967 and 197512. The subsequent recovery of the gulf’s reefs was slowed down again by the episode of the cooling of the Gulf’s waters due to the eruption of Mount Pinatubo in 1991. That event caused erosion of the Gulf’s thermocline and led to deep mixing of its waters, enriching surface waters with nutrients. The resulting proliferation and subsequent decomposition of seaweeds smothered some 25% of the juvenile corals13. The anthropogenic eutrophication of the Gulf due to the increase in fish farming until the farm closing14, also reduced the transparency of its waters by increasing the concentration of phytoplankton15. These events, as well as the forthcoming Red-Dead Canal, call for frequent, detailed monitoring of any changes in the situation of the coral reefs of the Gulf, as are evident in the reduction of live coral cover and species biodiversity.
    Since its early development, DL has been used in human facial discrimination16, handwriting recognition17, and forensic applications, such as fingerprint identification18 and voice analysis19.
    DL has also been applied to various coral reef studies, in which it was used to discriminate among benthos types: sand, urchins, and three types of branched corals: brain coral, massive favids, and dead coral20, as well as to distinguish between healthy and bleached corals (see, e.g.,21,22). Shihavuddin et al.20 demonstrated the capability of DL to identify five coral genera from large assemblages of underwater images. In a recent study identification among branched and brain corals, was reported23.
    In their research, Gómez Ríos et al.23 also distinguished among favids, brain coral, and three branched coral types: I, II, and III (an urchin, dead corals, and pavements based on an image mosaic).
    Among DL studies at species level discrimination the following datasets are noteworthy:
    The first dataset is the Pacific Labelled Corals (PLC) dataset, which contains 5,090 images from four locations: 1. Mo’orea (French Polynesia), 2. Northern Line Islands, 3. Nanwan Bay (Taiwan), and 4. Heron Reef (Australia). The PLC dataset contains: 251,988 annotations from these four locations made by a coral reef expert using a random point tool. In addition, six experts cross-annotated 200 images from each location21.
    The second dataset is the Mo’orea Labeled Corals (MLC) dataset that includes five coral classes: Acropora, Pavona, Montipora, Pocillopora, and Porites, and four non-coral classes: crustose coralline algae, turf algae, macroalgae and sand. The MLC dataset contains over 400,000 human expert annotations of 2055 Mo’orea island survey images (https://vision.ucsd.edu/datasetsAll).
    To apply DL to a coral reef dataset, there is no need to sample small fragments of corals for the subsequent tedious identification in the laboratory. DL enables direct classification of a large amount of photographs, in minimum time.
    The novelty of the present study is the application of a fully-automated DL-based methodology to an imaging dataset, for the classification of 11 common coral types from the set of species reported in the Gulf of Eilat11. We applied DL to over 5,000 underwater images taken specifically by us from a shallow reef in the Gulf of Eilat, with the aim of documenting the distribution of the test types in the sample reef.
    We demonstrated the power of DL, using shallow coral reefs in the Gulf of Eilat for comparison with its efficiency in other reef sites. That site allowed us to compare our DL data with the detailed manual coral surveys previously conducted on these reefs.
    Corals and reefs
    The nature and global importance of corals and the rapid destructive impact of Global Climate Change call for extensive and fast indexing and monitoring. Coral reefs cover less than 1% of the total area of the oceans and seas, yet they are the main repository of oceanic biodiversity (25% of all marine species)24. Extant hermatypic (reef-building) coral species are estimated at 3,23524, of which 100 were recorded in Eilat, Gulf of Aqaba, Northern Red Sea10. Hexacorals, based on six fold symmetry, or scleractinian corals are the most important hermatypic organisms25.
    The decline of reefs leads to the collapse of their entire complex ecosystem depending on the calcium carbonate skeletons of the corals intricate reef structures, for food and shelter. Hermatypic corals are home to symbiotic algae living within their cells in specialized organelles, the symbiosomes. Called zooxanthellae by their first reporter, Brandt26, these greenish microalgae limited to sunlit shallow waters (~ 0–120 m), provide the corals with energy through their photosynthesis27,28, which also stimulates calcification29.
    In most corals, the tentacles are retracted by day and spread out at night30 to catch plankton and other small organisms, while avoiding diurnal coral-feeding predators. This behaviour also optimizes the supply of oxygen for nocturnal respiration.
    Unlike in shallow water, corals satisfy their energy needs in the deep water and dim light by zooplankton consumption, as an energy supplement to the algal light-limited photosynthetic products (see review by Dubinsky and Iluz28).
    The photosynthetic activity of the zooxanthellae, raises the internal pH of the coral facilitating the skeletal calcification by “light enhanced calcification”31,32, a paradigm recently challenged by Cohen et al.33. Conversely, ocean acidification makes coral calcification more difficult.
    The future of coral reefs
    Coral reefs are exposed to many dangers because of global climate-change effects34,35, blast and cyanide fishing36, coral collection by the marine coral aquarium trade37, sunscreen use38, and light pollution interference with lunar cycle reproduction timing39. SCUBA diving pressure40. Anthropogenic eutrophication, acts synergistically with all the above listed detrimental factors, stimulating fast seaweed growth, that easily outcompete the slowly growing corals. The ensuing algal blooms, smother the coral colonies and prevent the settlement of juveniles41. Kaneohe Bay, a coral reef ecosystem at Oahu, Hawaii, illustrates the sensitivity of coral reefs to nutrient enrichment resulting from treated sewage disposal, leading to the reversible proliferation of seaweeds42. Fish cage farming released nutrients that affected the coral reefs in Eilat by causing deterioration in water quality due to eutrophication and by promoting seaweed growth and phytoplankton proliferation reducing the Gulf’s water transparency, thus reducing light necessary for symbiont photosynthesis, interfering with reproduction, increasing bio-erosion and epizootic infestation14.
    Coral species differ in their tolerance to climate change and coral bleaching43. Corals experience bleaching as water temperature increases and causes loss of the zooxanthellae, and subsequently of live coral tissue, resulting in wide spread coral mortality followed by reef destruction. Unless the algal population recovers within weeks, the bleaching results in widespread reef mortality44. The ongoing increase in atmospheric carbon dioxide since the industrial revolution leads to ocean acidification or lowering of ocean pH, and affects corals negatively by shifting the balance from skeletal aragonite deposition toward its dissolution4. In addition, light pollution by artificial light, even at the weakest intensities45,46, can cause the disruption of coral reproduction that is controlled by lunar periodicity47,48. The planned Red Sea–Dead Sea Conveyance49 will cause a change in the regime of the Gulf currents50. Such a change could reduce the supply of larvae of corals and other reef organisms, and have a far-reaching deleterious impact on reef systems.
    The real-time characteristics of DL tools are crucial for the rapid detection of reef damage allowing implementation of bioremediation measures. The DL characteristics are valuable tools assuring the health and long-term survival of the coral reefs in the Gulf of Eilat and worldwide.
    Deep learning
    The efficiency of the methodology of DL-based classification of coral species consists of efficient algorithms that reveal and extract common-patterns and features from large image datasets. Two popular schemes applied to coral reef data are the convolutional neural network (CNN)21 and deep belief net (DBN)21. A generic structure of CNN is a multi-layer, feed-forward, supervised neural network that recognizes objects from spatial-based images with little or no pre-processing. It consists of: (1) feature extraction (convolution layer); (2) distortion invariance (sub-sampling layer); and (3) classification (output layer). A DBN, consists of probabilistic models composed of multiple layers of random variables51.
    Any coral-reef classification should consist of five main steps:
    1.
    Taking sufficient high quality underwater images.

    2.
    Detecting the chosen coral and cropping its image.

    3.
    Downscaling the cropped images to 200 × 200 pixels.

    4.
    Preprocessing the images to compensate for different imperfections (e.g., blurring, colour change, sunlight wave patterns, sky colour, nekton scattering effects etc.).

    5.
    Labelling each one of the coral species is labelled.

    In case of an automatic model, Steps 3 and 4 may not be required.
    Traditional machine learning methods need extensive domain expertise, human intervention, and are only capable of what they were originally designed for.
    Additional works on growth modelling and quantification of morphological variation in coral types are due to, Kruszyński et al.52 and Chindapol et al.53. The former focused on the analysis of three-dimensional (3D) coral images scanned by X-ray tomography, and the latter, modelled the effects of flow on colony growth and shape, using analyzed advection–diffusion equations.
    The increased interest in DL has also been recently reflected in the analysis of previously published coral datasets. Specifically, recent work22 has demonstrated the efficiency of neural networks and DL in distinguishing among various marine benthos components such as bare ground, seagrass meadows, algal cover, sponges, and identified some coral species. Additional recent work has shown the capability of neural networks and DL to distinguish among coral species and live corals from bleached colonies (see, e.g.,21,22).
    Mahmood et al.22 combined CNN representations with manually obtained colony parameters. Their algorithms, based on image information, extract CNN images obtained from the deep VGGnet network with a 2-layer multilayer perceptron (MLP) classifier (trained on the MLC dataset). They achieved 77.9% accuracy.
    Mahmood et al.54, reviewed the power of DL for machine monitoring of coral reefs.
    Mahmood et al. (2016a)55 reported a decrease trend in coral density and species numbers in the reefs of Abrolhos Islands. Their analysis was based on CNN images obtained from VGGnet. They proved the reliability of their classifier on unlabelled coral image mosaics.
    Mahmood et al. (2018)56 used CNN-based features and ResFeats to annotate corals and demonstrated the temporal changes in their association. They applied generic features from VGGnet and ResNet to classify corals and non-corals. They analysed unlabeled coral mosaics of three Abrolhos Island sites generating maps for the aforementioned mosaics.
    Mahmood et al. (2020)57 applied computerized DL characterization of annotated kelp species. They presented an automatic hierarchical classification method to classify kelps in collected images. Their study summarises the considerable advantages of using deep residual networks (ResNets) over traditional, manual classifications of the same reefs. They showed that the sibling hierarchical training approach outperforms the traditional parallel multi-class classifications by a significant margin (90.0% vs. 57.6% and 77.2% vs. 59.0%) on Benthoz15 and Rottnest datasets, respectively. They used an application to study the changes in kelp cover over time for annually repeated AUV surveys.
    Mahmood et al. (2020)58 evaluated how well features extracted from deep neural networks transfer to underwater image classification. They investigated the effectiveness of transfer learning of the ResFeats. They proposed applying new image features (called ResFeats) extracted from the different convolutional layers of a deep residual network pre-trained on ImageNet to the MLC, Benthoz15, EILAT and RSMAS datasets.
    Gómez-Ríos et al.23 included more corals than previous studies by applying three CNNs: Inception v359, ResNet60, and DenseNet61 (see Supplementary Table 1).
    Two datasets were analysed: Both the EILAT and RSMAS were analysed. These datasets comprise patches of coral images discriminating branched and massive colonies. The EILAT dataset contains 1123 images of eight classes (sand, urchin, branched type I, II, and III corals, brain coral, favid coral, and dead coral) and the RSMAS dataset contains 776 images of 14 classes, including 9 classes of the following scleractinian coral species: Acropora cervicornis, Acropora palmata, Diploria strigosa, Montastraea cavernosa, Meandrina meandrites, Montipora spp., Siderastrea sidereal, Colpophyllia natans (a boulder brain coral), and the colonial fire coral Millepora alcicornis (a species of hydrozoa with a calcareous skeleton). The other five classes included in the RAMAS dataset are non-coral species: Diadema antillarum is a sea urchin, Gorgonians are a genus of soft corals in the family Gorgoniidae, Palythoas palythoa is a genus of anthozoans in the order Zoantharia, and sponge fungus and tunicates are marine invertebrates of the subphylum Tunicata.
    CoralNet (https://coralnet.ucsd/edu), conceived by Beijbom et al.9,62, uses deep neural networks for fully- or semi-automated image annotation. It also serves as a convenient, user-friendly collaboration platform. In early 2019, Williams et al.63 in a large study showed that the automated annotations for CoralNet Beta, produced benthic cover estimates comparable to controls gathered by human annotation.
    Hoegh-Guldberg states that “CoralNet will allow the world’s scientists to quickly assess the health of endangered coral reefs at scales never dreamed of before”, in (https://blogs.nvidia.com/blog/2016/06/22/deep-learning-save-coral-reefs/).
    The BenthoBox image labelling system for ecologists allows storing images of the dataset.
    The software uses learning algorithms to recognise ‘tagged’ seabed features such as sand, algae, sponges and corals.
    History of coral classification in the Gulf of Eilat
    Traditional methods have been used in Gulf of Eilat research studies for coral classification since the pioneering work by Loya and Slobodkin10. Some 100 coral species were listed in their study.
    Whenever confronted with doubt concerning the species of a certain coral underlying a transect, a small piece was sampled and manually identified by a taxonomist11, a tedious and destructive practice based on limited sample size.
    These surveys were based on colour photographs taken by a camera with a flash attachment. Close-ups were taken by a Rolleiflex camera. A measuring tape was spread over the reef, and the divers recorded the projected length of all the organisms and substrates underneath the line transect to a resolution of 1 cm. Photographs were taken at 1 m intervals along the transect. This study was based on permanent transects photographed over a period of 20 months that yielded about 3,000 photographs of corals belonging to Loya’s11 list of approximately 100 species. However, the author noted that many cryptic species do not show up in the photographs.
    Similar additional surveys were conducted following various disturbances that affected the coral reefs of the Gulf: the 1970 low tide64, the repeated oil spills65, the Pinatubo eruption of 199166, and the fish farming episode of 1995–200814.
    Diver-based methods for classifying corals are almost impossible underwater, and require time-consuming expertise. Furthermore, coral pigmentation and morphology are plastic changes in response to environmental forcing functions such as light and current, eliciting wide phenotypic variability28,67. Ever since the National Monitoring Program (https://www.iuieilat.ac.il/Research/NMPmeteodata.aspx) of the Eilat reefs was initiated (2003), annual surveys by divers have been conducted.
    The images are taken at a fixed area at six reef sites, namely the North Beach, the Dekel Beach, the Eilat Ashkelon Pipeline Co. Ltd. (EAPC), the coral reserve, the Interuniversity Institute for Marine Sciences in Eilat (IUI) marine laboratory, and Taba. Each site has fixed camera brackets for five cameras, and each of these takes four images. In this way, 20 pictures are taken at each site, and 120 pictures are taken for quantitative analysis of the changes at the various sites. Monitoring is done once a year in early summer. Corals were identified as far as possible at the species level, and were also classified according to functional groups. The results are presented graphically following statistical processing. Due the disintegration of the rock to which the cameras were attached, some new sites had to be added68.
    Automated DL seeks to avoid these difficulties, profiting from the latest advances in computerized handling of large quantities of visual images9. Indeed, these novel developments have been increasingly applied to the survey and analysis of coral reefs in the studies listed in Supplementary Table 2. Since all previous surveys, as well as those of the current monitoring program of the Gulf of Eilat reefs, were based on the manual and visual analysis of large numbers of photographs, we present here a first example at using automated machine-based analysis for the red sea coral reef. More