Strong currents are a key component of benthic habitats by supplying food and nutrients to filter-feeding organisms such as cold-water corals. Although field measurements show that cold-water coral habitats exist in areas of elevated bottom currents, flume studies show that cold-water corals feed more effectively at lower flow speeds. This research aims to explore this disconnect in situ by utilising high spatial resolution ROV photogrammetric data coupled with high temporal resolution in situ acoustic doppler current profile measurements at seven study sites within the upper Porcupine Bank Canyon (uPBC), NE Atlantic. Object-based image analysis of photogrammetric data show that coral habitats vary considerably within the upper canyon. Although there is a regional hydrodynamic trend across the uPBC, this variation is likely driven locally by topographic steering. Although live coral tends not to face directly into the prevailing current direction, preferring lower local flows speeds, they can tolerate exposure to high-flow speeds of up to 114 cm s−1, the highest recorded in a Desmophyllum pertusum habitat. Not only do these high flow speeds supply food and nutrients, they may also help contribute to coral rubble production through physical erosion. These results can be incorporated into simulations of future deep-water habitat response to changing environmental conditions while extending the upper current speed threshold for cold-water corals.

Submarine canyons support high biomass communities as they act as conduits where sediments, nutrients, and organic matter from continental shelves, or those that are carried along by slope currents, are transported into the abyssal zone. The Porcupine Bank Canyon (PBC), located on the Irish continental margin and isolated from terrigenous inputs, reveals a complex terrain and substrate variation that affect the distribution of benthic fauna. Here, ROV-based benthic video, conductivity-temperaturedepth (CTD), current velocity profiles, suspended particulate organic matter (POM) and bathymetric data were assessed to determine the controls on the distribution of benthic megafauna throughout the canyon. Multivariate analysis of the benthic community reveals significant differences in community structure among habitats and site locations throughout the canyon. Furthermore, these results show that non-reef habitats exhibit more variation in the composition of benthic taxa than coral reef and rubble habitats, with the following species contributing most to the structural differentiation between habitats: Leiopathes glaberrima (12.46%), Hexadella dedritifera (10.37%), Cidaris cidaris (9.31%), Aphrocallistes beatrix (9.33%), Araeosoma fenestratum (9.11%), Stichopathes cf. abyssicola (7.39%), Anthomastus grandiflorus (4.66%), and Benthogone rosea (3.84%). In addition, greater diversity, taxa evenness and high abundance of motile fauna were observed in non-reef habitat and the canyon flank. Seabed terrain features (depth, slope) are the most important environmental drivers that affect benthic taxa distribution while site locations and habitat type are the categorical variables that influence taxa distribution in the PBC. The highest mean current speed was observed on the canyon flank where the highest Shannon's diversity was recorded while mean current speed ranged from 18.2-31.3 cm s −1. As the PBC is cut off from direct terrigenous input, this research contributes to understanding cold-water coral habitat responses to natural

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The “Little MonSta” benthic lander array consists of 8 ROV-deployable (remotely operated vehicle) instrumented lander platforms for monitoring physical and chemical oceanographic properties and particle sampling developed as part of the MMMonKey_Pro program (mapping, modeling, and monitoring key processes and controls in cold-water coral habitats in submarine canyons). The Little MonStas offer flexible solutions to meet the need to monitor marine benthic environments during a historically unprecedented time of climate-driven oceanic change, develop an understanding of meso-scale benthic processes (natural and man-made), and to calibrate geological environmental archives. Equipped with acoustic Doppler current profilers (ADCPs), sediment traps, nylon settlement plates and homing beacons, the compact and upgradable lander platforms can be deployed by ROVs to precise locations in extreme terrains to a water depth of 3000 m. The array allows cluster-monitoring in heterogeneous environments or simultaneous monitoring over wider areas. A proof-of-concept case study was presented from the cold-water coral habitable zone in the upper Porcupine Bank Canyon, where the Little MonStas collected 868.8 h of current speed, direction, temperature, and benthic particulate flux records, as well as 192 particle samples subsequently analyzed for particular organic carbon (POC), lithic sediment, live foraminifera, and microplastics. The potential to upgrade the Little MonStas with additional sensors and acoustic releases offers greater and more flexible operational capabilities.

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