Habitat variability and faunal zonation at the Ægir Ridge, a canyon-like structure in the deep Norwegian Sea

Abstract

The Ægir Ridge System (ARS) is an ancient extinct spreading axis in the Nordic seas extending from the upper slope east of Iceland (∼550 m depth), as part of its Exclusive Economic Zone (EEZ), to a depth of ∼3,800 m in the Norwegian basin. Geomorphologically a rift valley, the ARS has a canyon-like structure that may promote increased diversity and faunal density. The main objective of this study was to characterize benthic habitats and related macro- and megabenthic communities along the ARS, and the influence of water mass variables and depth on them. During the IceAGE3 expedition (Icelandic marine Animals: Genetics and Ecology) on RV Sonne in June 2020, benthic communities of the ARS were surveyed by means of a remotely-operated vehicle (ROV) and epibenthic sledge (EBS). For this purpose, two working areas were selected, including abyssal stations in the northeast and bathyal stations in the southwest of the ARS. Video and still images of the seabed were usedtoqualitatively describebenthic habitats based on the presence of habitat-forming taxa and the physical environment. Patterns of diversity and community composition of the soft-sediment macrofauna, retrieved from the EBS, were analyzed in a semiquantitative manner. These biological data were complemented by producing high-resolution bathymetric maps using the vessel’s multi-beam echosounder system. As suspected, we were able to identify differences in species composition and number of macro- and megafaunal communities associated with a depth gradient. A biological canyon effect became evident in dense aggregates of megafaunal filter feeders and elevated macrofaunal densities. Analysis of videos and still images from the ROV transects also led to the discovery of a number ofVulnerable Marine Ecosystems (VMEs) dominated by sponges and soft corals characteristic of the Arctic region. Directions for future research encompass a more detailed, quantitative study of the megafauna and more coherent sampling over the entire depth range in order to fully capture the diversity of the habitats and biota of the region. The presence of sensitive biogenic habitats, alongside seemingly high biodiversity and naturalness are supportive of ongoing considerations of designating part of the ARS as an “Ecologically and Biologically Significant Area” (EBSA).

Beyond the tip of the seamount: Distinct megabenthic communities found beyond the charismatic summit sponge ground on an arctic seamount (Schulz Bank, Arctic Mid-Ocean Ridge)

“…the summit, though further investigation is needed. These geodiid-dominated walls of Schulz Bank resemble similar communities observed around Mohn's Treasure (73 • 44 ′ N 7 • 27 ′ E), an inactive sulphide mound on AMOR just south of the Schulz Bank (Ramirez-Llodra et al, 2020), and on the AEgir Ridge System (Brix et al, 2022), a rift valley with a canyon-like structure extending from 700 m to 3800 m depth. On Mohn's Treasure, the bedrock walls were dominated by similar sponges (with a density of 22.4 ind.…”

“…m − 2 ), crinoids and decapods to those observed on Schulz Bank (Ramirez-Llodra et al, 2020). On AEgir Ridge, geodiid-dominated communities covered the steeply sloping area of the ridge, where consolidated sediment layers were present (Brix et al, 2022). It is interesting to note that the main structure-forming demosponge taxa found on the lower slopes of Schulz Bank, Mohn's Treasure, and AEgir Ridge are the same that form the summit sponge grounds found on seamounts in the Central Arctic Ocean (Morganti et al, 2022).…”

Variations in Volcanism and Tectonics Along the Hotspot‐Influenced Reykjanes Ridge

“…Despite suggested excess magmatism, and hence, heat input into the ridge system, the Reykjanes Ridge is characterized by an apparent paucity of high‐temperature hydrothermal vents with presently only two known vent fields: the Steinahóll (∼63°06′N) and IceAGE (∼60°N) hydrothermal fields (Brix et al., 2020; German et al., 1994; J. Taylor et al., 2021).…”

A new deep-sea species of Halirages Boeck, 1871 (Crustacea: Amphipoda: Calliopiidae) inhabiting sponges

“…A remotely operated vehicle (GEOMAR ROV KIEL 6000) captured in situ video footage images of the abyssal plain at station 37 (3700-3450 m) from the sedimented plain in the median valley towards the rise of the Aegir Ridge System (Ránarhryggur) northwest of Iceland by RV Sonne in 2020 (Brix et al 2020). The transect showed a highly sedimented habitat with sparse rocky outcrops in the abyssal plain area (Brix et al 2022). Occasional rocks were colonized by the glass sponge Caulophacus arcticus (Hansen, 1885) (Brix et al 2022).…”

“…The transect showed a highly sedimented habitat with sparse rocky outcrops in the abyssal plain area (Brix et al 2022). Occasional rocks were colonized by the glass sponge Caulophacus arcticus (Hansen, 1885) (Brix et al 2022). The colonies of C. arcticus provide a habitat for aggregations of caridean shrimp (Bythocaris cf.…”