Bathymetric Position Index Research Articles

Biogeophysical influence of large-scale bathymetric habitat types on mesophotic and upper bathyal demersal fish assemblages: a Hawaiian case study

Seamounts, pinnacles, and crests are abrupt seafloor features that modify physical processes and ecological patterns. Fishers often target these local bathymetric highs, which can have high catch-per-unit-effort. Increases in the abundance of target species has been qualitatively noted around these features and promontories, however, a quantitative evaluation of local highs as preferred habitat for fishes is still lacking. Here, we used an extensive database of fish abundances (N = 2381) from mesophotic and upper bathyal depths (40-300 m) gathered over 8 yr around the Main Hawaiian Islands to evaluate the effects of macro-scale habitat categorized by combining bathymetric position index (BPI) and slope. A numerical model simulating physical ocean processes was used to test the hypothesis that local highs, herein called crests, are distinct and preferred habitat for many species due to their modified flow conditions. We show that crests host a unique, diverse fish assemblage with double the abundance relative to other habitats. Therefore, fishes are concentrated at crests rather than being uniformly distributed along the island shelf at preferred depths. These habitats are characterized by enhanced current amplitudes and convergence zones. Direct correlations between fish abundance, convergence, and current amplitude strongly suggest that flow-enhanced food availability is likely the driver of habitat-related changes in fish assemblage. These results have important implications for conservation and management. We identify a simple and informative method to classify habitat, quantitatively link bathymetry-induced flow alterations to fish abundances, and provide information for refining definitions of essential fish habitat for species that are important commercial targets worldwide.

Submarine landslides: mapping the susceptibility in European seas

A map of susceptibility to submarine landslides in European seas has been developed using the maximum entropy model (MaxEnt) and landslide cartography acquired from European Marine Observation and Data Network (EMODnet) Geology ( https://www.emodnet-geology.eu/ ). A total of 15% landslide points were set aside and used as test data, while the remaining 85% were used for model training. Based on EMODnet bathymetry, 33 environmental maps including bathymetric position index (BPI), slope, features, flat curvature and profile curvature, all calculated at different spatial scales, were processed. In an iterative process, all the variables that were highly collinear and those that did not contribute significantly to the model were eliminated. In the end, the model was constructed using only bathymetry and the slope of the seabed. The elaborated model has an area under the ROC (receiver operating characteristic) curve (AUC) of 0.910 calculated on the training set and 0.911 on the test set, and the ROC curves are coincident. The slope is the variable that gives the greatest contribution to the model (82%), but without the contribution of depth (18%) the results degrade significantly. The susceptibility map correctly identifies all the main structures where the presence of landslides is known. The model shows a certain sensitivity to bathymetric acquisition noise. Thematic collection: This article is part of the Mapping the Geology and Topography of the European Seas (EMODnet) collection available at: https://www.lyellcollection.org/cc/EMODnet

Distribution and Suitable Habitat of the Cold-Water Corals Lophelia pertusa, Paragorgia arborea, and Primnoa resedaeformis on the Norwegian Continental Shelf

Cold-water corals are habitat-forming species that are also classified as indicators of Vulnerable Marine Ecosystems (VMEs) due to the threat of various anthropogenic impacts e.g. fisheries and oil/mineral exploration. To best protect VMEs, knowledge of their habitat requirements and distribution is essential. However, comprehensive sampling of the deep sea is difficult due to access and cost constraints, so species distribution modeling (SDM) is often used to predict overall distributions and ecological preferences of species based on limited data. We used Maximum Entropy (Maxent) modeling to predict the probability of presence of the reef-building scleractinian Lophelia pertusa and the octocorals Paragorgia arborea and Primnoa resedaeformis using a total of 2149 coral presence points and 15 environmental predictor variables. The environmental variables used in the analysis were processed to 176m resolution and included bathymetry, depth, geomorphometric characteristics (slope, aspect and bathymetric position index (BPI)), oceanography (temperature, salinity, current directions and speed), surface chlorophyll a concentration, sediment type, and marine landscape type. Comparing presence points with environmental data showed that the temperature and depth range for Lophelia was narrower compared to the gorgonians, and it occurred in shallower, warmer water. Observations showed that Lophelia had a broad, bimodal response to Broad BPI, while the predicted model indicated a more narrow response. Paragorgia tolerated the greatest range of sloping according to the model. All three species were observed with a bimodal pattern along a wide range of mean current speed, while the models indicated a high response to faster current speed. Jackknife tests showed that sediment type was an important predictor for gorgonian corals, while BPI and minimum temperature were more important for Lophelia. The spatial precision of the models could be further increased by applying environmental layers with a higher and uniform spatial resolution. The predicted distribution of corals and their relation to environmental variables provides an important background for prioritizing areas for detailed mapping surveys and will aid in the conservation efforts for these VMEs in Norwegian waters and beyond.

Nearshore Sandbar Classification of Sabaudia (Italy) with LiDAR Data: The FHyL Approach

An application of the FHyL (field spectral libraries, airborne hyperspectral images and topographic LiDAR) method is presented. It is aimed to map and classify bedforms in submerged beach systems and has been applied to Sabaudia coast (Tirrenyan Sea, Central Italy). The FHyl method allows the integration of geomorphological observations into detailed maps by the multisensory data fusion process from hyperspectral, LiDAR, and in-situ radiometric data. The analysis of the sandy beach classification provides an identification of the variable bedforms by using LiDAR bathymetric Digital Surface Model (DSM) and Bathymetric Position Index (BPI) along the coastal stretch. The nearshore sand bars classification and analysis of the bed form parameters (e.g., depth, slope and convexity/concavity properties) provide excellent results in very shallow waters zones. Thanks to well-established LiDAR and spectroscopic techniques developed under the FHyL approach, remote sensing has the potential to deliver significant quantitative products in coastal areas. The developed method has become the standard for the systematic definition of the operational coastal airborne dataset that must be provided by coastal operational services as input to national downstream services. The methodology is also driving the harmonization procedure of coastal morphological dataset definition at the national scale and results have been used by the authorities to adopt a novel beach management technique.

A preliminary study on spatial assessment using conservation metrics for intertidal oyster reefs at the Hab River mouth in Pakistan

The oyster reefs in Pakistan are on the verge of extinction as a consequence of environmental and anthropogenic factors. A qualitative survey of oyster reef habitat was conducted from March-2017 to February-2018 in the Hab River Delta along the Balochistan coast (Arabian Sea), Pakistan. A combination of field survey and Geographical Information System (GIS) based approach (reef categorization, universal metrics and habitat suitability analysis), universal environmental variables, restoration goal-based metrics, sounding, condition indices, grain size composition and oyster spat-fall were determined for planning future oyster reef restoration efforts. The reefs were categorized into three main groups as dispersed, patch and continuous on the basis of fragmented spatial geometry. Dispersed reefs were more numerous than continuous and patch categories. The differences between morphometric measurements and density of oysters amongst reefs types were statistically insignificant. Habitat suitability analysis was done by ‘Benthic Terrain Modeler’ using ArcGIS software. The moderate, positive values of Bathymetric Position Index (BPI) of the oyster reef indicate an area of high or open slope with sea bottom (-2 to 6). The area of reef location shows high to moderate values of rugosity (0.7 to 0.9), indicates good to intermediate conditions; whereas, the aspect analysis showed slope orientation in the Northeast direction but mostly flat area. The environmental and restoration goal-based metrics were favorable for oyster growth and survival. The dispersed reefs showed lowest bathymetry points compared to patch and continuous reefs. The values of condition indices reveal not significant difference among reef types (continuous, dispersed and patch). Fine sand has the highest percentage (71%) followed by silt/clay fraction (18%). The higher density and spat size were recorded in monsoon (June to September) season. The current study suggests that the present reefs are viable and have potential for successful restoration and may be converted into a sizeable ecologic sanctuary.

Patterns in Bathyal Demersal Biodiversity and Community Composition Around Archipelagos in the Tropical Eastern Pacific

Deep-sea fauna of the Tropical Eastern Pacific (TEP) have remained largely un-described because exploration has historically been a challenge in these remote locations. Consequently, little is currently known about deep-ocean biodiversity in the TEP. An enriched understanding of biogeographic patterns and the factors that influence them is crucial to the success of efforts to conserve deep-sea communities. The objectives of this research were to provide the first assessment of biodiversity and community composition of bathyal demersal (200 - 3,000m) fauna across multiple ocean/island archipelagos in the TEP. To better understand biodiversity and its drivers in the region, we tested the hypotheses that biodiversity and faunal assemblage composition vary with location and environmental drivers (e.g bathymetry, oxygen concentration). Using Deep-Ocean Dropcams, we collected video footage from Clipperton, Galapagos, Revillagigedos, and Malpelo, in depths ranging from 200 to 3,000 m. Taxa richness, Shannon diversity, and Simpson diversity were calculated for each location. In general, biodiversity values were high closer to the equator and closer to the continent, and low in the locations farther north and farther west. Fish family biodiversity was highest in the Galapagos, followed by Malpelo. In contrast, Clipperton had significantly lower fish family richness compared to all other locations. For invertebrate orders, the Revillagigedos were significantly lower in biodiversity compared to the Galapagos and Malpelo. Broad-scale Bathymetric Position Index (BPI) and dissolved oxygen had a positive effect on fish diversity metrics. Both fish and invertebrate assemblages were significantly different among locations. Around each of the island groups are vastly different current patterns, which likely accounts for some of the variation we observed in biodiversity and community composition. Due to the longitudinal East Pacific Rise, which limits population connectivity by creating a spatial barrier to gene flow and dispersal among marine organisms, the TEP is largely isolated from the wider Pacific. The islands and archipelagos likely represent important stepping-stones and corridors for species connectivity across the TEP and the wider Pacific. Therefore, the preservation of these intact ecosystems is crucial for maintaining biodiversity both within the TEP as well as across the wider Pacific region.

Generating higher resolution regional seafloor maps from crowd-sourced bathymetry.

Seafloor mapping can offer important insights for marine management, spatial planning, and research in marine geology, ecology, and oceanography. Here, we present a method for generating regional bathymetry and geomorphometry maps from crowd-sourced depth soundings (Olex AS) for a small fraction of the cost of multibeam data collection over the same area. Empirical Bayesian Kriging was used to generate a continuous bathymetric surface from incomplete and, in some areas, sparse Olex coverage on the Newfoundland and Labrador shelves of eastern Canada. The result is a 75m bathymetric grid that provides over 100x finer spatial resolution than previously available for the majority of the 672,900 km2 study area. The interpolated bathymetry was tested for accuracy against independent depth data provided by Fisheries and Oceans Canada (Spearman correlation = 0.99, p<0.001). Quantitative terrain attributes were generated to better understand seascape characteristics at multiple spatial scales, including slope, rugosity, aspect, and bathymetric position index. Landform classification was carried out using the geomorphons algorithm and a novel method for the identification of previously unmapped tributary canyons at the continental shelf edge are also presented to illustrate some of many potential benefits of crowd-sourced regional seafloor mapping.

Characterization and Mapping of a Deep-Sea Sponge Ground on the Tropic Seamount (Northeast Tropical Atlantic): Implications for Spatial Management in the High Seas

Ferromanganese crusts occurring on seamounts are a potential resource for rare earth elements that are critical for low-carbon technologies. Seamounts, however, host vulnerable marine ecosystems (VMEs), which means that spatial management is needed to address potential conflicts between mineral extraction and the conservation of deep-sea biodiversity. Exploration of the Tropic Seamount, located in an Area Beyond National Jurisdiction (ABNJ) in the subtropical North Atlantic, revealed large amounts of rare earth elements, as well as numerous VMEs, including high-density octocoral gardens, Solenosmilia variabilis patch reefs, xenophyophores, crinoid fields and deep-sea sponge grounds. This study focuses on the extensive monospecific grounds of the hexactinellid sponge Poliopogon amadou (Thomson, 1878). Deep-sea sponge grounds provide structurally complex habitat, augmenting local biodiversity. To understand the potential extent of these sponge grounds and inform spatial management, we produced the first ensemble species distribution model and local habitat suitability maps for P. amadou in the Atlantic employing Maximum Entropy (Maxent), General Additive Models (GAMs), and Random Forest (RF). The main factors driving the distribution of the sponge were depth and maximum current speed. The sponge grounds occurred in a marked bathymetric belt (2,500 – 3,000 m) within the upper North Atlantic Deep Water mass (2.5∘C, 34.7 psu, O2 6.7–7 mg ml-1), with a preference for areas bathed by moderately strong currents (0.2 – 0.4 ms-1). GAMs, Maxent and RF showed similar performance in terms of evaluation statistics but a different prediction, with RF showing the highest differences. This algorithm only retained depth and maximum currents whereas GAM and Maxent included bathymetric position index, slope, aspect and backscatter. In these latter two models, P. amadou showed a preference for high backscatter values and areas slightly elevated, flat or with gentle slopes and with a NE orientation. The lack of significant differences in model performance permitted to merge all predictions using an ensemble model approach. Our results contribute toward understanding the environmental drivers and biogeography of the species in the Atlantic. Furthermore, we present a case toward designating the Tropic Seamount as an Ecologically or Biologically Significant marine Area (EBSA) as a contribution to address biodiversity conservation in ABNJs.

Using the random forest algorithm to integrate hydroacoustic data with satellite images to improve the mapping of shallow nearshore benthic features in a marine protected area in Jamaica

Hydroacoustic and optical remote sensing have been commonly used to map shallow nearshore benthic features. However, the number, type, scale, and accuracy of the mapping products that can be obtained from the two sensors differ; as such, there can be limited agreement between their mapping products. These differences can be further accentuated if the hydroacoustic data are interpolated to produce a map. Interpolation introduces spatial uncertainty and reduces map accuracy. Consequently, maps generated from the two sensors may provide dissimilar spatial and temporal representations of the same benthic features. We therefore compared the performance of a random forest regression (RFr) and a universal kriging (UK) interpolation method and a post-classification enhancement that can be used to increase the accuracy and complementarity of benthic habitat maps derived from hydroacoustic data. First, we used single beam echosounder (SBES) survey bathymetry data from the Bluefields Bay marine protected area (MPA) in western Jamaica (13.82 km2 in size), to create a bathymetric surface model (BSM), from which rugosity and bathymetric position index (BPI) maps were generated. Next, the RFr was used to create submerged aquatic vegetation (SAV) percentage cover maps from the SBES SAV cover data by predicting cover at un-sampled locations. Predictors included auxiliary data such as depth, BPI, survey points coordinates and radiometrically corrected, deglinted and water column corrected image reflectance index values from each of the following: WorldView-2, Geoeye-1 and Landsat 8. Additionally, a SAV map was created using the UK. The most accurate SAV cover thresholds were identified and were used to create binary maps from the RFr and UK maps. A rugosity derived coral reef map was then added to the binary maps. The resulting benthic habitat maps had comparable accuracies and class coverage to benthic maps classified from GeoEye-1 and WorldView-2 images using pixel and object-based classifiers. However, map accuracies were calculated using a suboptimal number of reference points (<50) for two of the benthic map classes (SAV absent and coral reef). This was not considered to be problematic as the addition of the coral reef class to the binary maps resulted in a significant decrease in uncertainty (standard error and confidence interval width of the overall accuracy) and a significant increase in the user’s accuracy of the SAV absent map class. Also, the difference in uncertainty and accuracy between the map classes did not change. The methods used in this study can therefore be used to increase the accuracy (and to decrease the uncertainty) and the complementarity of maps derived from hydroacoustic data.

Benthic habitat modelling and mapping as a conservation tool for marine protected areas: A seamount in the western Mediterranean

Abstract An ecologically representative, well‐connected, and effectively managed system of marine protected areas (MPAs) has positive ecological and environmental effects as well as social and economic benefits. Although progress in expanding the coverage of MPAs has been made, the application of management tools has not yet been implemented in most of these areas. In this work, distribution models were applied to nine benthic habitats on a Mediterranean seamount within an MPA for conservation purposes. Benthic habitat occurrences were identified from 55 remotely operated vehicle (ROV) transects, at depths from 76 to 700 m, and data derived from multibeam bathymetry. Generalized additive models (GAMs) were applied to link the presence of each benthic habitat to local environmental proxies (depth, slope, backscatter, aspect, and bathymetric position index, BPI). The main environmental drivers of habitat distribution were depth, slope, and BPI. Based on this result, five different geomorphological areas were distinguished. A full coverage map indicating the potential benthic habitat distribution on the seamount was obtained to inform spatial management. The distribution of those habitats identified as vulnerable marine ecosystems (VMEs) was used to make recommendations on zonation for developing the management plan of the MPA. This process reveals itself as an appropriate methodological approach that can be developed in other areas of the Natura 2000 marine network.

Predicting important rockfish (Sebastesspp.) habitat from large-scale longline surveys for southern British Columbia, Canada

Rockfish, particularly yelloweye (Sebastes ruberrimus) and quillback (Sebastes maliger), are vulnerable to overfishing because they mature late and have affinity for shallow water (50–200 m) habitats. Because studies relating habitat characteristics with the distribution and presence of rockfishes at large scales (100s of kilometres) remain scarce, we sought to investigate the relationships between benthic characteristics with the presence–absence and abundance of rockfishes caught in longline surveys in nearshore waters of southern British Columbia. Habitat parameters were calculated from a 20 m resolution bathymetry layer. Yelloweye and quillback were examined separately and combined with 19 other rockfish species in a species aggregate (total rockfish); occurrence data were fitted with generalized linear mixed effects models, and abundance data were fitted with zero-inflated mixed effects models. The relationship between rockfish abundance with presence–absence and slope, distance to rocky habitat, and fine bathymetric position index suggests that these species prefer rocky, steep habitat. While underwater visual observation data offer measures of visual fish habitat and abundance, longline surveys may be a more cost-effective method for large-scale studies.

Classification of Coral Reefs in the South China Sea by Combining Airborne LiDAR Bathymetry Bottom Waveforms and Bathymetric Features

Geographic information describing coral reefs plays an important role in constructing electronic chart systems and protecting the ecological environment of the ocean. To derive geographic information of coral reefs more effectively, this paper proposes a methodology to detect coral reefs by combining airborne LiDAR bathymetry (ALB) bottom waveform and bathymetric feature data. A feature vector was established by deriving bottom waveform variables (the peak amplitude, pulsewidth, area, skewness, kurtosis, and backscatter cross section) and bathymetric variables (the depth standard deviation, slope, bathymetric position index, Gaussian curvature, mean curvature, and roughness). Using a support vector machine classifier, coral reefs were detected by distinguishing two classes (coral reefs and others) on the seafloor. To evaluate the classification performance of coral reefs, the developed method was applied to Yuanzhi Island, South China Sea surveys, and verified by field data (aerial digital camera images and underwater video images). The results showed that the classification overall accuracy of coral reefs can be greatly improved from 80.59%/90.31% when ALB bottom waveform or bathymetric variables features were used separately to 93.57% when using a combination of ALB bottom waveform and bathymetric features. In addition, the kappa coefficient can also be greatly improved from approximately 0.61/0.80 to 0.87. And the new proposed method performs better compared to the current classification method using ALB data to detect coral reefs with an overall accuracy of 90.92% and Kappa of 0.81. This highlights the potential of ALB data, combining waveform data and bathymetric data, for precisely detecting coral reefs in shallow water areas.

Geodiversity evaluation of the Słupsk Bank boulder area

The Słupsk Bank is a seascape area of high nature value, that consists of boulders related to glacial and post-glacial formation and a variety of underwater landforms, that form the habitat for numerous plants and animals. The aim of this paper was to evaluate geodiversity using geoinformation analysis consecutive steps, such as preparation of factor maps, map algebra etc. The resulting geodiversity map was based on a bathymetric relief energy map, a geomorphological map based on expert classification using the Bathymetric Position Index (BPI), and a lithological map showing average texture classes of sediments). Maps of geodiversity support the identification and delimitation of the geodiversity hotspots for nature protection, as well as the directions for management of valuable natural areas.

AUV-based classification of benthic communities of the Ningaloo shelf and mesophotic areas

Despite a growing understanding of the importance of mesophotic ecosystems, they remain relatively unexplored globally, and particularly in the Indian Ocean. The composition of benthic communities of the Ningaloo Marine Park in deeper water (> 20 m) was determined using autonomous underwater vehicles (AUVs). Environmental variables collected by the AUVs as well as geomorphological variables derived from high-resolution multibeam bathymetry were used to explain the distribution of these communities. Imagery was classified for benthic biota, and non-hierarchical k-means clustering was used to identify community groups. Overall, 12 community groups were identified which fell into three broad categories: (1) coral-dominated, (2) CCA-dominated; and (3) macroalgae- and filter-feeder-dominated. Specific deeper water communities (> 50 m) were characterised by the presence of sponges or other non-photosynthetic filter feeders. Corals were confined to depths < 40 m, and cover was high (29–40%). Generalised additive models identified the importance of substrate (cover of sand, rock, and gravel/pebbles), geomorphological variables (slope and bathymetric position index) and temperature in the distribution of communities.

Geomorphology and Late Pleistocene–Holocene Sedimentary Processes of the Eastern Gulf of Finland

In 2017, a detailed study of the Eastern Gulf of Finland (the Baltic Sea) seafloor was performed to identify and map submerged glacial and postglacial geomorphologic features and collect data pertinent to the understanding of sedimentation in postglacial basins. Two key areas within the Gulf were investigate using a multibeam echosounder, SeaBat 8111 and an EdgeTech 3300-HM acoustic sub-bottom profiling system. High-resolution multibeam bathymetric data (3-m resolution) were used to calculate aspect, slope, terrain ruggedness and bathymetric position index using ArcGIS Spatial Analyst and the Benthic Terrain Modeler toolbox. These data and resultant thematic maps revealed, for the first time, such features as streamlined till ridges, end-moraine ridges, and De Geer moraines that are being used for the reconstruction of the deglaciation in the Eastern Gulf of Finland. This deglaciation occurred between 13.8 and 13.3 ka BP (Pandivere–Neva stage) and 12.25 ka BP (Salpausselkä I stage). Interpretations of the seismic-reflection profiles and 3D models showing the surfaces of till, and the identification of the Late Pleistocene sediment and modern bottom relief, indicate deep relative water-level fall in the Early Holocene and, most likely, several water-level fluctuations during this time.

Quantitative characterization of subaqueous landslides in Lake Zurich (Switzerland) based on a high-resolution bathymetric dataset

Abstract New high-resolution surveying techniques allow subaqueous geomorphology to be investigated in great detail. Such analyses are important as the morphologies are often indicative of past processes, including mass movements. For peri-alpine Lake Zurich, many mass-wasting events have occurred in the past millennia. While the ages of these events are known from past studies on the respective deposits in the lake basin, the surface expressions and distribution of the respective features on the slopes have not been extensively described. Here we quantitatively characterize the morphologic features on the entire lake floor. A total of 50 subaqueous landslides are morphologically identified in a high-resolution digital bathymetric model (DBM), mapped and characterized using a geographic information system (GIS). Many slides show relatively small erosion areas (&lt;0.05 km 2 ) and are located in shallow water (&lt;10 m water depth). The roughness of the individual landslide-translation areas is quantified using the standard deviation of a measure called bathymetric position index (BPI) and related to the slides ages. The DBM allows the detection of traces of mass-movements dating back to c. 5000 cal years BP. Our results demonstrate that morphometric analyses on a high-resolution DBM can contribute to a better understanding of sublacustrine mass movements.

Santa Maria di Leuca Province (Mediterranean Sea): Identification of Suitable Mounds for Cold-Water Coral Settlement Using Geomorphometric Proxies and Maxent Methods

The Santa Maria di Leuca (SML) cold-water coral province (northern Ionian Sea) has the largest occurrence of a living white coral community currently known in the Mediterranean Sea. Madrepora oculata and Lophelia pertusa, identified as marking sensitive habitats of relevance by the General Fisheries Commission for the Mediterranean, have been observed heterogeneously distributed on the summits of several mounds. This particularly patchy and uneven distribution in addition to their importance for regional biodiversity highlights the need to better understand their environmental preferences and predict their distribution. Bathymetric data (40m resolution) was used to derive the seafloor characteristics. A fine scale index quantifying the landscape elevation (Bathymetric Position Index at 120m resolution) was used to select all the elevated features considered as candidate morphologies for potential coral mounds. Statistics on 22 known coral topped mounds were computed. Two statistical methods were then used to identify other potential coral mounds based on predictive variables. The first method, the Geomorphometric proxies method, consists in computing basic statistics of terrain variables, using them for a step-by-step classification in a quantitative approach to select a subset of candidate morphologies. The second method consists in using a predictive Habitat Suitability Model (Maxent model). The Geomorphometric proxies method identified 736 potential coral mounds while the Maxent method predicted 1252 potential coral mounds. A subset of 517 potential coral mounds was common to both methods. The analysis of the contribution of each variable with the Maxent method showed that the variable "Vector Ruggedness Measure" at a resolution of 5 pixels (200 m) contributed to 53% of the final Maxent model, followed by the "Terrain Texture" index (31%) at a resolution of 11 pixels (440 m). The common potential coral mounds are mainly located in an area characterized by a mass transport deposit, also called the mounds area because of the roughness of the seafloor, in accordance with the high proportional contribution of the noticeable first roughness index to the Maxent model. The results highlight the importance of the global conservation of the entire Province, with white coral probably widespread over the entire 600 km² SML area.

Hard-bottom bathyal habitats and keystone epibenthic species on Le Danois Bank (Cantabrian Sea)

“El Cachucho” Marine Protected Area (MPA), which comprises Le Danois Bank and its intraslope basin, was included during 2008 in the Nature 2000 network mainly because of the presence of the habitat “1170 Reefs” according to the EU Habitat Directive. To review the effectiveness of existing management measures, several activities aimed at characterizing the most structurally complex hard-bottom habitats were planned and carried out during the ESMAREC 0514 survey. For identification of these habitats, several transects using the photogrammetric towed sled Politolana were carried out on Le Danois Bank, in the depth range between 427 and 1379m, searching for the sea beds with higher values of slope and backscatter. Photogrammetric techniques were used for image scaling, so we could determine the surface areas of different substrata types (facies) and their species densities. A total area of 28,762m2 was analyzed in the still images of 23 transects, verifying that 85% of the substrata of our study area are occupied by 4 different facies: Bedrock, bedrock with mixed sediments, mixed sediments with pebbles and boulders, and mixed sediments. Acoustic data and ground-truth visual data were combined to evaluate distinctive benthic scenarios. The relative abundances of the 123 epibenthic species identified by image analyses show that the most abundant are sponges (29%), cnidarians (26%), crustaceans (26%) and echinoderms (14%), i.e. mostly sessile species or those with low mobility. The keystone species of the “1170 Reefs” habitat are 3 cnidarians: Callogorgia verticillata, Paramuricea cf. placomus and Dendrophyllia cornigera, and 3 sponges, Asconema setubalense, Geodia msp.1 and Phakellia robusta. Eight new habitats (biotopes) have been identified on Le Danois Bank, six of which occur on the hard bottoms, with depth, substratum, BPI (Bathymetric Position Index) and slope as determining environmental variables that explain their spatial distributions.

Multisource multibeam backscatter data: developing a strategy for the production of benthic habitat maps using semi-automated seafloor classification methods

The establishment of multibeam echosounders (MBES) as a mainstream tool in ocean mapping has facilitated integrative approaches towards nautical charting, benthic habitat mapping, and seafloor geotechnical surveys. The bathymetric and backscatter information generated by MBES enables marine scientists to present highly accurate bathymetric data with a spatial resolution closely matching that of terrestrial mapping, and can generate customized thematic seafloor maps to meet multiple ocean management needs. However, when a variety of MBES systems are used, the creation of objective habitat maps can be hindered by the lack of backscatter calibration, due for example, to system-specific settings, yielding relative rather than absolute values. Here, we describe an approach using object-based image analysis to combine 4 non-overlapping and uncalibrated (backscatter) MBES coverages to form a seamless habitat map on St. Anns Bank (Atlantic Canada), a marine protected area hosting a diversity of benthic habitats. The benthoscape map was produced by analysing each coverage independently with supervised classification (k-nearest neighbor) of image-objects based on a common suite of 7 benthoscapes (determined with 4214 ground-truthing photographs at 61 stations, and characterized with backscatter, bathymetry, and bathymetric position index). Manual re-classification based on uncertainty in membership values to individual classes—especially at the boundaries between coverages—was used to build the final benthoscape map. Given the costs and scarcity of MBES surveys in offshore marine ecosystems—particularly in large ecosystems in need of adequate conservation strategies, such as in Canadian waters—developing approaches to synthesize multiple datasets to meet management needs is warranted.

Processing and performance of topobathymetric lidar data for geomorphometric and morphological classification in a high-energy tidal environment

Abstract. The transition zone between land and water is difficult to map with conventional geophysical systems due to shallow water depth and often challenging environmental conditions. The emerging technology of airborne topobathymetric light detection and ranging (lidar) is capable of providing both topographic and bathymetric elevation information, using only a single green laser, resulting in a seamless coverage of the land–water transition zone. However, there is no transparent and reproducible method for processing green topobathymetric lidar data into a digital elevation model (DEM). The general processing steps involve data filtering, water surface detection and refraction correction. Specifically, the procedure of water surface detection and modelling, solely using green laser lidar data, has not previously been described in detail for tidal environments. The aim of this study was to fill this gap of knowledge by developing a step-by-step procedure for making a digital water surface model (DWSM) using the green laser lidar data. The detailed description of the processing procedure augments its reliability, makes it user-friendly and repeatable. A DEM was obtained from the processed topobathymetric lidar data collected in spring 2014 from the Knudedyb tidal inlet system in the Danish Wadden Sea. The vertical accuracy of the lidar data is determined to ±8 cm at a 95 % confidence level, and the horizontal accuracy is determined as the mean error to ±10 cm. The lidar technique is found capable of detecting features with a size of less than 1 m2. The derived high-resolution DEM was applied for detection and classification of geomorphometric and morphological features within the natural environment of the study area. Initially, the bathymetric position index (BPI) and the slope of the DEM were used to make a continuous classification of the geomorphometry. Subsequently, stage (or elevation in relation to tidal range) and a combination of statistical neighbourhood analyses (moving average and standard deviation) with varying window sizes, combined with the DEM slope, were used to classify the study area into six specific types of morphological features (i.e. subtidal channel, intertidal flat, intertidal creek, linear bar, swash bar and beach dune). The developed classification method is adapted and applied to a specific case, but it can also be implemented in other cases and environments.