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Physiculus cynodon is a member of the Moridae family and possesses a ventral bioluminescent organ. Although it has been captured by commercial vessels for decades, our understanding of its biology and ecology remains fragmented. This paper provides data on the species’ spatial and vertical distributions; age and growth; size, age, sex compositions; and sex ratio in the waters around the Emperor Seamounts and the northwestern Hawaiian Ridge. This information is based on the analysis of multi-year Russian data obtained from scientific surveys and observations on commercial fishing vessels. The northernmost capture of this species has been recorded at Nintoku Seamount. Additionally, this species was regularly encountered at depths ranging from 53 to 900 m on seamounts such as Lira (Annei), Koko, Milwaukee (Yuryaku and Kammu), Colahan, and C-H of the Emperor Seamounts and Hancock, Zapadnaya, and Academician Berg of the northwestern Hawaiian Ridge. Catch rates of P. cynodon gradually decreased in a southeastern direction. Notably, the relative abundance of this species in bottom trawl catches significantly surpasses that in pelagic catches. The age of the fish in the catch varied from 9 to 37 years, and its growth is described by the VBGF equation with the following coefficients: L∞ = 858.6, k = 0.030, t0 = 3.5. While the growth patterns for males and females were similar, it is worth mentioning that males rarely survive beyond the age of 25 years.

Detailed descriptions of morphological features, morphometrics, neurocranium anatomy, clasper structure and egg case descriptions are provided for the thickbody skate Amblyraja frerichsi; a rare, deep-water species from Chile, Argentina and Falkland Islands. The species diagnosis is complemented from new observations and aspects such as colour, size and distribution are described. Geographic and bathymetric distributional ranges are discussed as relevant features of this taxons biology. Additionally, the conservation status is assessed including bycatch records from Chilean fisheries.

Abstract The discharge of hydrothermal vents on the seafloor provides energy sources for dynamic and productive ecosystems, which are supported by chemosynthetic microbial populations. These populations use the energy gained by oxidizing the reduced chemicals contained within the vent fluids to fix carbon and support multiple trophic levels. Hydrothermal discharge is ephemeral and chemical composition of such fluids varies over space and time, which can result in geographically distinct microbial communities. To investigate the foundational members of the community, microbial growth chambers were placed within the hydrothermal discharge at Axial Seamount (Juan de Fuca Ridge), Magic Mountain Seamount (Explorer Ridge), and Kamaʻehuakanaloa Seamount (Hawai'i hotspot). Campylobacteria were identified within the nascent communities, but different amplicon sequence variants were present at Axial and Kamaʻehuakanaloa Seamounts, indicating that geography in addition to the composition of the vent effluent influences microbial community development. Across these vent locations, dissolved iron concentration was the strongest driver of community structure. These results provide insights into nascent microbial community structure and shed light on the development of diverse lithotrophic communities at hydrothermal vents. Microbial diversity is quickly established in growth chambers incubated at hydrothermal vents and nascent communities are driven by chemistry and location.

We present new observations on the dynamics and locations of deep mantle reservoirs derived from the ages and compositions of Voyager Seamount Chain lava flows. The previously unexplored Voyager Seamount Chain trends NW–SE between the Mid‐Pacific Mountains and the Northwestern Hawaiian Ridge. Volcanic samples were recovered from the chain during the Ocean Exploration Trust expedition NA134. The lava flows are alkalic to highly alkalic in composition. Ages ranged from 81 to 86 Ma (n = 8), with the oldest ages in the NW and an age‐progression toward the SE. The Voyager age‐progression continues southward through the Northern Line Islands region until at least 69 Ma. Mantle flowlines using absolute plate motion models indicate that the Voyagers were emplaced near the modern Marquesas Hotspot location approximately 86–69 Ma. The Sr‐Nd‐Pb‐Hf isotope systematics show the influence of an EMII component and overlap the compositions of Pliocene volcanism from the Marquesas Islands, consistent with the plate motion age model. These data imply a long‐lived plume as the source of the Voyager seamounts and the Marquesas. However, the lack of a clear and continuous seamount chain between the 86–69 Ma Voyager Seamount Chain and the 6–0 Ma Marquesas Islands implies that the mantle plume displays variable buoyancy flux over time. The surface expression of this mantle reservoir experienced a potential hiatus of up to ∼60 m.y. These new data indicate that the mantle beneath the Marquesas Islands region has been discontinuously producing age‐progressive, EMII‐like hotspot volcanism since at least the Late Cretaceous.

[This corrects the article DOI: 10.1371/journal.pbio.3000366.].

The formerly continuous Vitiaz Arc broke into its Vanuatu and Fijian portions during a reversal of subduction polarity in the Miocene. Basaltic volcanism in Fiji that accompanied the breakup ranged from shoshonitic to low‐K and boninitic with increasing distance from the broken edge of the arc that, presumably, marks the broken edge of the slab. The Sr‐Pb‐Nd isotope ratios of the slab‐derived component in the breakup basalts most closely match those of the isotopically most depleted part of the Samoan seamount chain on the Pacific Plate that was adjacent to the site of breakup at 4–8 Ma, and differ from those of subsequent basalts in spreading segments of the surrounding backarc North Fiji and Lau Basins. Subduction of the Samoan Chain along the Vitiaz Trench Lineament may have controlled the limit of polarity reversal and, hence, where the double saloon doors (Martin, 2013) opened. Prior to breakup, Fijian volcanics were more similar isotopically to the Louisville Seamount Chain. Plain Language Summary The subduction zone that included Tonga and Fiji was once connected to Vanuatu. We attribute the arc breakup to subduction of the Samoan Seamount Chain. Volcanism in Fiji accompanying breakup ranges from shoshonitic closest the tear in the arc, to low‐K and boninitic farthest from it. The ambient mantle source of magma during breakup was the same as earlier in arc history but the slab‐derived component changed during breakup. Post‐breakup volcanism came from different mantle unaffected by subduction and derived from beneath the Pacific Plate. Key Points The breakup between Fiji and Vanuatu may have been triggered by subduction of Samoan seamounts Shoshonitic to low‐K and boninitic volcanism accompanied breakup with increasing distance from the break The mantle source of later basalts in surrounding backarc basins and islands came from beneath the Pacific Plate north of the breakup site

Seamounts are isolated elevations in the seafloor with circular or elliptical plans, comparatively steep slopes, and relatively small summit area (Menard, 1964). The vertical gravity gradient (VGG), which is the curvature of the ocean surface topography derived from satellite altimeter measurements, has been used to map the global distribution of seamounts (Kim & Wessel, 2011, https://doi.org/10.1111/j.1365-246x.2011.05076.x). We used the latest grid of VGG to update and refine the global seamount catalog; we identified 19,325 new seamounts, expanding a previously published catalog having 24,643 seamounts. Seven hundred thirty‐nine well‐surveyed seamounts, having heights ranging from 421 to 2,500 m, were used to estimate the typical radially symmetric seamount morphology. First, an Empirical Orthogonal Function (EOF) analysis was used to demonstrate that these small seamounts have a basal radius that is linearly related to their height—their shapes are scale invariant. Two methods were then used to compute this characteristic base to height ratio: an average Gaussian fit to the stack of all profiles and an individual Gaussian fit for each seamount in the sample. The first method combined the radial normalized height data from all 739 seamounts to form median and median‐absolute deviation. These data were fit by a 2‐parameter Gaussian model that explained 99.82% of the variance. The second method used the Gaussian function to individually model each seamount in the sample and further establish the Gaussian model. Using this characteristic Gaussian shape we show that VGG can be used to estimate the height of small seamounts to an accuracy of ∼270 m. Key Points We used the latest vertical gravity gradient maps to update and refine a global seamount catalog, finding 19,325 new seamounts Smaller seamounts (<2,500 m tall) having good bathymetry coverage (739) were modeled with a radially symmetric Gaussian function Two modeling approaches show that smaller seamounts have a sigma to height ratio of 2.4 which agrees with an earlier study by Smith (1988)

Vulnerable marine ecosystems (VMEs) are ecosystems at risk from the effects of fishing or other kinds of disturbance, as determined by the vulnerability of their components (e.g., habitats, communities or species). Habitat suitability modelling is being used increasingly to predict distribution patterns of VME indicator taxa in the deep sea, where data are particularly sparse, and the models are considered useful for marine ecosystem management. The Louisville Seamount Chain is located within the South Pacific Regional Fishery Management Organisation (SPRFMO) Convention Area, and some seamounts are the subject of bottom trawling for orange roughy by the New Zealand fishery. The aim of the present study was to produce high-resolution habitat suitability maps for VME indicator taxa and VME habitat on these seamounts, in order to evaluate the feasibility of designing within-seamount spatial closures to protect VMEs. We used a multi-model habitat suitability mapping approach, based on bathymetric and backscatter data collected by multibeam echo sounder survey, and data collected by towed underwater camera for the stony coral and habitat-forming VME indicator species Solenosmilia variabilis, as well as two taxa indicative of stony coral habitat (Brisingida, Crinoidea). Model performance varied among the different model types used (Boosted Regression Tree, Random Forest, Generalized Additive Models), but abundance-based models consistently out-performed models based on presence-absence data. Uncertainty for ensemble models (combination of all models) was lower overall compared to the other models. Maps resulting from our models showed that suitable habitat for Solenosmilia variabilis is distributed around the summit-slope break of seamounts, and along ridges that extend down the seamount flanks. Only the flat, soft sediment summits are predicted to be unsuitable habitat for this stony coral species. We translated a definition for stony coral-reef habitat into a Solenosmilia variabilis abundance-based threshold in order to use our models to map this VME habitat. These maps showed that coral-reef occurred in small and isolated patches, and that most of the seabed on these seamounts is predicted to be unsuitable habitat for this VME. We discuss the implications of these results for spatial management closures on the Louisville Seamount Chain seamounts and the wider SPRFMO.

Volcanic seamount chains on the flanks of mid‐ocean ridges record variability in magmatic processes associated with mantle melting over several millions of years. However, the relative timing of magmatism on individual seamounts along a chain can be difficult to estimate without in situ sampling and is further hampered by Ar40/Ar39 dating limitations. The 8°20’N seamount chain extends ∼170 km west from the fast‐spreading East Pacific Rise (EPR), north of and parallel to the western Siqueiros fracture zone. Here, we use multibeam bathymetric data to investigate relationships between abyssal hill formation and seamount volcanism, transform fault slip, and tectonic rotation. Near‐bottom compressed high‐intensity radiated pulse, bathymetric, and sidescan sonar data collected with the autonomous underwater vehicle Sentry are used to test the hypothesis that seamount volcanism is age‐progressive along the seamount chain. Although sediment on seamount flanks is likely to be reworked by gravitational mass‐wasting and current activity, bathymetric relief and Sentry vehicle heading analysis suggest that sedimentary accumulations on seamount summits are likely to be relatively pristine. Sediment thickness on the seamounts' summits does not increase linearly with nominal crustal age, as would be predicted if seamounts were constructed proximal to the EPR axis and then aged as the lithosphere cooled and subsided away from the ridge. The thickest sediments are found at the center of the chain, implying the most ancient volcanism there, rather than on seamounts furthest from the EPR. The nonlinear sediment thickness along the 8°20’N seamounts suggests that volcanism can persist off‐axis for several million years. Plain Language Summary Most of the volcanism on Earth happens in the oceans, at mid‐ocean ridges where plates spread apart. In some places, however, chains of volcanoes that extend over distances of hundreds of kilometers long can form away from the ridge axis. The formation of these volcanic chains, called off‐axis seamounts, is poorly understood, yet understanding their origins will help learn about processes taking place deep inside Earth's mantle. We used a sonar carried by an underwater robot in water depths of ∼3 km to measure the thickness of sedimentary mud on top of a seamount chain in the eastern Pacific Ocean at 8°20’N. The thicker the sediment, the greater the time that has passed since the last volcanic eruption. We found that sediments do not simply thicken with seafloor age, implying that volcanoes in these types of seamount chains can remain active over millions of years. Key Points Regional bathymetry and near‐bottom sonar surveys investigate the structure and history of the 8°20’N seamount chain, west of the East Pacific Rise (EPR) Sediment thickness from autonomous underwater vehicle subbottom compressed high‐intensity radiated pulse images are used to estimate the relative age of magmatism at nine seamounts along chain Sediment thickness does not increase with distance from the EPR axis, implying that magmatism was episodic and prolonged

Valdivia Bank is an oceanic plateau in the South Atlantic formed by hot spot magmatism at the Mid‐Atlantic Ridge during the Late Cretaceous. It is part of the Walvis Ridge, an aseismic ridge and seamount chain widely considered to be formed by age‐progressive volcanism from the Tristan‐Gough plume. To better understand the formation and history of this edifice, we developed a bathymetric map of Valdivia Bank by merging available multibeam echosounder data sets with a bathymetry grid based mainly on satellite altimetry (SRTM15+). The bathymetric map reveals previously unresolved features including extensive rift grabens, volcanic mounds and knolls, and large‐scale sediment transport systems. After Valdivia Bank was emplaced and probably eroded at sea level, it underwent a period of rifting, followed by a secondary magmatic pulse that caused regional uplift to sea‐level, followed by subsidence to current depths. Shallow banks at depths of ∼1,000 m are the result of a thick sediment pile atop uplifted volcanic crust. Several shallower mounds (∼1,000–520 m) and a guyot (∼220 m) likely resulted from coral reef growth atop one or more volcanic pedestals formed during the younger Cenozoic magmatic event. As sediments accumulated on the shallow platforms, sediment transport systems developed as gullies, channels and mass transport deposits carved valleys and troughs, shedding sediment into abyssal fans at the plateau base. The new bathymetric map demonstrates that oceanic plateaus are geologically active long after initial emplacement. Plain Language Summary Valdivia Bank is an oceanic plateau in the South Atlantic that was formed as part of Walvis Ridge by hot spot volcanism at the Mid‐Atlantic Ridge. Walvis Ridge topography is more complex than that of simple hot spot tracks. Moreover, younger‐than‐expected ages from dredge samples suggest a second phase of volcanism. To better understand the development of this plateau, we created a detailed bathymetry map by compiling available multibeam echosounder data with satellite‐altimetry‐based depth estimates. The map reveals previously unseen features including rifts, volcanic mounds, and submarine slides and sediment drainage features. These suggest that after Valdivia Bank formed, it underwent faulting, followed by volcanism that raised the plateau to sea level. Subsequently, the plateau subsided while accumulating a thick sediment cover. Shallow banks resulted from thick sediments atop the uplifted basement. Several shallower mounds likely resulted from coral reef growth atop a volcanic base formed during the later stage of volcanism. As sediments accumulated atop the plateau, they were shed through gullies, channels and submarine slides, carving valleys and troughs, and then deposited around the plateau base. Our findings demonstrate that oceanic plateaus can be geologically active long after their formation. Key Points A bathymetry map was constructed for Valdivia Bank from multibeam data merged with satellite altimetry‐predicted depths Valdivia Bank experienced extension, forming rifts, and secondary volcanism, uplift, and exposure, then was capped by carbonate sediments Valdivia Bank shows evidence of mass wasting, partly triggered by Cenozoic uplift and erosion, but also owing to sediment cap instability