Deep-sea biodiversity at the extremes of the Salas y Gómez and Nazca ridges with implications for conservation

Pacific [41]. Given the high rate of discovery of new species, this region may well harbor many more undiscovered marine species [51, 52]. Depth, crust age, broad-scale BPI, and nitrate explained the most variation in both inverte- brate and fish assemblages on our camera deployments, and our findings are largely consistent with other studies [45, 82, 87]. Community composition on seamounts is depth stratified, reflecting environmental gradients that correlate with depth, such as temperature, oxygen con- centration, food availability, and pressure [32]. The high habitat heterogeneity on seamounts, quantified by BPI, combined with the biological effects of depth, increases local biodiversity by Table 2. SIMPER for fish families most responsible for the percent dissimilarities between subregions using Bray-Curtis similarity analysis of hierarchical agglom- erative group average clustering. Families Des RN/SyG Diss. Contrib% Cum% Squalidae 2.26 (2.49) 0.21 (0.54) 16.63 (0.89) 18.27 18.27 Moridae 0.63 (1.04) 0.26 (0.56) 7.27 (0.69) 7.98 26.25 Macrouridae 0.37 (0.69) 0.53 (1.02) 6.65 (0.68) 7.31 33.56 Halosauridae 0.41 (0.97) 0.37 (0.68) 6.25 (0.63) 6.87 40.43 Synaphobranchidae 0.30 (0.67) 0.47 (0.70) 6.18 (0.64) 6.80 47.22 Pentacerotidae 1.04 (2.9) - 5.65 (0.39) 6.21 53.43 Gempylidae - 0.58 (0.90) 5.57 (0.55) 6.12 59.55 Cheilodactylidae 0.85 (3.05) - 3.12 (0.27) 3.42 62.97 Carangidae 0.28 (1.53) 0.16 (0.97) 2.97 (0.32) 3.27 66.24 Etmopteridae 0.22 (0.42) - 2.50 (0.47) 2.75 68.99

Chimaeridae 0.07 (0.27) 0.16 (0.50) 2.45 (0.40) 2.69 71.68 Sebastidae 0.37 (1.18) - 2.33 (0.30) 2.56 74.24 Ophidiidae 0.30 (1.20) - 2.19 (0.26) 2.41 76.65 Serranidae 0.30 (1.35) 0.53 (2.29) 2.14 (0.35) 2.35 79.00 Labridae 0.15 (0.77) 0.16 (0.69) 1.58 (0.23) 1.74 80.73 Lutjanidae - 0.58 (2.29) 1.53 (0.31) 1.68 82.41 Triglidae 0.26 (0.53) - 1.45 (0.45) 1.59 84.00 Polymixiidae 0 (0) 0.16 (0.50) 1.39 (0.29) 1.52 85.53 Monocentridae 0.22 (0.64) - 1.21 (0.34) 1.32 86.85 Myctophidae 0.07 (0.27) 0.05 (0.23) 1.12 (0.35) 1.23 88.08 Alepocephalidae 0.07 (0.27) - 1.05 (0.24) 1.15 89.23 Hexanchidae - 0.11 (0.46) 0.98 (0.22) 1.08 90.31 Average dissimilarity = 91.08%. Values are average MaxN with one standard deviation of the mean in parentheses. DES = Desventuradas, Diss. = dissimilarity, Contrib % = percent contribution to dissimilarity, Cum% = cumulative percent contribution to dissimilarity. https://doi.org/10.1371/journal.pone.0253213.t002 Table 3. Distance-based linear model for fish assemblages and environmental variables. Sequential tests Multiple partial correlations Variable AICc SS(trace) Pseudo-F P Prop. Cumul. dbRDA1 dbRDA2 Depth 371.18 39264 12.903 0.001 0.227 0.227 0.947 -0.006 Salinity 369.90 10021 3.479 0.001 0.058 0.285 0.264 -0.384 Crust age 369.08 8370 3.044 0.002 0.048 0.333 -0.033 -0.81 Nitrate 368.34 7924 3.020 0.003 0.046 0.379 0.166 0.385 BPI broad 367.83 7136 2.842 0.007 0.041 0.420 0.076 0.217

Multiple partial correlations are the relationships between dbRDA coordinate axes and orthonormal X variables. Prop. = proportion of variation explained. Cumul. = cumulative proportion variation explained. https://doi.org/10.1371/journal.pone.0253213.t003 PLOS ONE Deep-sea biodiversity along the Salas y Go´ mez and Nazca ridges PLOS ONE | https://doi.org/10.1371/journal.pone.0253213 June 30, 2021 16 / 27