Oasis of the deep: cold-water corals of the South China Sea-supporting information

HD video data were split into several frame sequences, which were used to evaluate the occurrence, density, and distribution of coral communities. Poor quality video data, including duplicates, out-of-focus video, or video with poor visibility, were removed from the image analysis process. Species were enumerated and identified to the lowest possible taxon or morphology based on visual observation. Morphologically similar corals that could not be identified from the records were grouped at higher taxonomic levels. Unfortunately, identification from images was difficult when diagnostic characters were not conspicuous. The correspondence between the visual assignment of an individual to a particular coral species and its actual taxonomic classification was verified through the collection of samples. Three major anthozoan taxonomic groups (gorgonians, black corals, and stony corals) were observed in our study, and these taxa were the most conspicuous and easily identified by imaging. Each coral species was identified and calculated for each still frame when the individual coral was completely in the field of view. The visual field of the video images covered an average area of 2.4 m2 when the submersible maintained an average altitude of 2 m above the seafloor. However, the width of the field of view varies with the tilt angle of the camera, which may affect the accurate estimation of the field of view.CWC communities were classified according to (i) habitat, (ii) substrate type, (iii) depth layer, (iv) temperature layer, (v) salinity layer, and (vi) size class to be used for statistical analyses. To characterize the coral colonies, most transects of dives focused on the northwestern ridge of these habitats. The depth data were divided into distinct layers with a 100 m depth interval based on the depth of the dominant coral communities. Observations of CWCs during the submersible survey were plotted as different groups corresponding to temperature (from 2 to 10.0°C) and salinity (from 34.33 to 34.60 psu). A total of 30 layers were divided according to depths between 300 and 3900 m, and 14 and 10 different layers based on temperature and salinity, respectively. To further describe and analyze the distribution structure of coral communities, corals were classified according to size as small (< 30 cm), medium (30–50 cm), medium to large (50–100 cm), and large (>100 cm).The relative abundance of different CWC species was estimated by dividing the total counts of individual coral species covered per 100 m depth interval by the sum of individual species. Moreover, the relative abundance of individual coral species in different habitats was also calculated by dividing total counts of individual coral species covered per habitat by the total number of the coral species in the habitat. The relative abundance of individual coral species according to sizes or substrates was evaluated in a similar manner. Density was calculated for CWCs by dividing the total number of individuals by the total area covered.