Fig 1.
A regional map showing the location of Cobb Seamount (46° 44 N, 130° 48' W), approximately 500 km off the west coast of Canada and the USA, in the international waters of the Northeast Pacific Ocean.
The exclusive economic zones are outlined. Map produced using www.geomapapp.org and the global multi-resolution topography synthesis [22].
Fig 2.
The location of submersible-collected images (circles) on Cobb Seamount.
The imagery of the shallow seamount summit (<211 m) was collected using a remotely operated vehicle (ROV) while the imagery of the deeper flanks was collected using an autonomous underwater vehicle (AUV). Point locations of the images analysed are overlaid on shaded multibeam bathymetry where contour lines represent 100 m depth intervals.
Fig 3.
Representative photographs of the nine Cobb Seamount communities.
(1) The hard substrate of the pinnacle carpeted in epifauna, including Desmarestia viridis macroalgae and Mesocentrotus franciscanus sea urchins. (2) Shallow, hard substrates with dense assemblages of Florometra serratissima crinoids on encrusting Corallinales spp. algae and Halichondria panicea sponge. (3) Hard substrates with a mix of Corallinales spp. and Stylaster spp. hydrocorals, supporting a rich assemblage of Sebastes spp. rockfishes. (4) Bare, hard substrate with small patches of the Laqueus californianus lamp shells and schools of the large Sebastes and S. melanostictus rockfishes (indistinguishable from images; recorded as one taxon). (5) A mix of hard and fine substrates, both covered in Stylaster spp. (living corals on hard, dead pieces and rubble on sand). (6) The flat, sandy edge of the seamount summit, with patches of Ophiura sarsii and Asteronyx loveni brittle stars, and Pagurus kennerlyi hermit crabs. (7) Sand and gravel on the seamount flanks, with sparse Actiniaria sp. anemones and Sebastolobus spp. thornyheads. (8) Exposed hard substrate on the deep flanks, with high-density Alcyonacea corals (e.g., Paragorgia sp.) and Hexactinellida sponges (e.g., Pinulasma fistulosoma). (9) Deep bedrock and gravel supporting a variety of Antipatharia spp. corals (e.g., Lillipathes cf lillei and Bathypathes sp.). Photo credit: DFO Pacific Biological Station ROV team, NOAA Northwest Fisheries Science Center and the Pacific Islands Fisheries Science Center AUV team.
Table 1.
The ecological summary statistics of the nine Cobb Seamount communities identified by the present study.
Table 2.
Taxon richness and number of unique taxa of the nine Cobb Seamount communities.
Table 3.
The frequency of each collection dive and each substrate type observed (as a percentage of the images that recorded each community), and the mean and range of the four environmental variables measured at the sample (i.e., image) locations for each community on Cobb Seamount.
Fig 4.
The environmental data (depth, slope, and small- and large-scale ACR rugosity) at the image locations for each of the nine Cobb Seamount communities.
The boxes represent the inter-quartile interval, circles represent outliers, stars represent extreme outliers, and horizontal lines represent the median. The superscript letters represent the output of the Mann-Whitney U tests, where community locations that are significantly different to each other do not share a common letter.
Fig 5.
Non-metric multidimensional scaling (NMDS) ordination plots showing the ecological and environmental (dis)similarity between and within nine communities on Cobb Seamount.
NMDS plots were generated from Bray-Curtis similarity matrices of the faunal data for (A) all nine communities, (B) Communities 1 to 6, and (C) Communities 7 to 9. Similarly, NMDS plots were generated from Euclidian similarity matrices of the environmental data for (D) all nine communities, (E) Communities 1 to 6, and (F) Communities 7 to 9. Faunal data were for the presence-absence of 74 taxa, while environmental data include depth, slope, and small- and large-scale rugosity. Each community is represented by a different symbol and encircled by 95% similarity ellipses. The NMDS axes are unique for each plot.
Fig 6.
Outputs from the Random Forest modelling.
(A) The predicted distributions of the nine communities, plus the hypothesized Lophelia pertusa bioherm community, and (B) the degree of model uncertainty. Model resolution is 20 by 20 m, thin black lines represent 100 m depth contours, the thick black line represents 1200 m (the approximate depth limit of the image surveys). (A) Each community is represented by a different colour, (B) white circles represent image locations, hatching represents the depth gap not surveyed (211 to 472 m), and dark gray shading represents extrapolated areas (i.e., areas where one or more environmental variable is beyond the sampled range).
Table 4.
A summary of the distributional and environmental characteristics of ten communities on Cobb Seamount based on a predicted distribution model (Fig 6A), and a hypothesized unsampled Lophelia pertusa Bioherm community.