Rybakova E et al. (2020), Vertical distribution of megafauna on the Berin...

ECB-ART-48520

PeerJ 2020 Jan 01;8:e8628. doi: 10.7717/peerj.8628.

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Vertical distribution of megafauna on the Bering Sea slope based on ROV survey.

Rybakova E , Galkin S , Gebruk A , Sanamyan N , Martynov A .

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Video surveys were carried out during the 75th cruise of the RV Akademik M.A. Lavrentyev (June 2016) along the northern slope of the Volcanologists Massif, in the south-western Bering Sea. The seafloor was explored using the ROV Comanche 18. Seven dives were performed in the depth range from 4,278 m to 349 m. Overall, about 180 species of megafauna were recognised. Fifteen types of megafauna communities corresponding to certain depth ranges were distinguished based on the most abundant taxa. Dominance changed with depth in the following order: the holothurian Kolga kamchatica at the maximum depth (4,277-4,278 m); the holothurian Scotoplanes kurilensis at 3,610-2,790 m; the ophiuroid Ophiura bathybia at 3,030-2,910 m; benthic shrimps of the family Crangonidae at 2,910-2,290 m; the holothurian Paelopatides solea at 2,650-2,290 m; benthic jellyfish from the family Rhopalonematidae at 2,470-2,130 m; the enteropneust Torquaratoridae at 2,290-1,830 m; the holothurian Synallactes chuni and the ophiuroid of the genera Ophiura and Ophiocantha at 1,830-1,750 m. At depths 1,750-720 m most of the megafauna was associated with live or dead colonies of the sponge Farrea spp. Depths 720-390 m were dominated by the coral Heteropolypus ritteri and/or Corallimorphus pilatus. At 390-350 m depth, the shallowest depth range, the dominant taxon was the zoantharian Epizoanthus sp. Soft sediment megafauna communities dominated by torquaratorid enteropneusts to our knowledge have not been observed before in the deep-sea, the same as communities with a dominance of benthopelagic rhopalonematid jellyfish. The depths of the largest community changes, or the largest turnover of dominant species, were revealed at ∼2,790 m between the bathyal and abyssal zones and ∼1,750 m and ∼720 m within the bathyal zone.

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Genes referenced: LOC100887844 LOC105441782

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	Figure 1. The tracks of the 7 ROV Comanche 18 dives on the northern slope of the Volcanologists Massif, in the south-west Bering Sea (75th cruise of RV Akademik M.A. Lavrentyev, June 2016).Five of the dives are broken up further into quantitative transects as explained in Table 1.
	Figure 2. The results of the cluster analysis of soft sediment communities (from quantitative transects) based on the Bray–Curtis similarity index.The colour indicates the depth range of clustered transects. The black dotted horizontal line corresponds to the 56% similarity level—the level at which the distinct groups of megafauna communities were distinguished. Transects that cannot be significantly differentiated based on SIMPROF tests were connected by red dotted lines (p < 0.05).
	Figure 3. The contribution to total abundance (in %) of the most abundant taxa in each of the clustered depth zones.
	Figure 4. Images of dominant megafauna at different depths.(A) 4,277–4,278 m, the holothurian Kolga kamchatica. (B) 3,610–3,450 m, the holothurian Scotoplanes kurilensis. (C) 3,030–2,910 m, the ophiuroid Ophiura bathybia and the holothurian S. kurilensis. (D) 2,910–2,790 m, the holothurian S. kurilensis, the ophiuroid O. bathybia and the shrimp Crangonidae gen. sp. (E) 2,790–2,650 m, the shrimp Crangonidae gen.sp. (F) 2,650–2,470 m, the holothurian Paelopatides solea and the shrimp Crangonidae gen. sp.
	Figure 5. Images of dominant megafauna at different depths (continued).(A) 2,470–2,290 m, the holothurian Paelopatides solea, the shrimp Crangonidae gen. sp. and the jellyfish Rhopalonematidae gen. sp. (B) 2,290–2,130 m, the jellyfish Rhopalonematidae gen. sp. and the enteropneust Torquaratoridae gen. sp. (C) 2,130–1,830 m, the enteropneust Torquaratoridae gen. sp. (D) 1,830–1,750 m, the holothurian Synallactes chuni and the ophiuroid (Ophiura spp. and Ophiocantha spp.). (E) 1,750–1,370 m, ophiuroids, the holothurian S. chuni and the glass sponge Farrea spp. (F) 1,370–720 m, the sponge Farrea spp. and ophiuroids. (G) 720–440 m, the cnidarian Heteropolypus ritteri. (H) 440–390 m, the cnidarian H. ritteri and Corallimorphus pilatus. (I) 390–350 m, the cnidarian Epizoanthus sp.
	Figure 6. The bathymetric distribution of the dominant megafaunal species.Each symbol corresponds to the occurrence of a species at a certain depth based on video. The three types of markers show the species status according to the following scale: “dominant”—was more abundant than any other species, “common”—occurred often and was relatively abundant and “rare”—was only met a few times). The dotted lines show the depths with the largest megafauna community changes (the depths of the largest turnover of dominant taxa).
	Figure 7. The number of identified species, aggregated into several major taxonomic groups, that occur between depths with the largest community changes.

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Grange, High Abundance of the Epibenthic Trachymedusa Ptychogastria polaris Allman, 1878 (Hydrozoa, Trachylina) in Subpolar Fjords along the West Antarctic Peninsula. 2017, Pubmed