. Rapid climate change is impacting Canada's northern coastlines, including northern fish, benthic ecosystems, and ecosystem services. Ongoing environmental pressures continue to influence the social, cultural, and physiological well-being of Labrador Inuit, who are intrinsically linked with the marine environment. Collaborating closely with the Nunatsiavut Government, this research presents a detailed map of benthic faunal assemblages in an understudied northern inshore system, providing essential information on benthic habitats and incorporating community-identified fishing locations for ogak (Greenland cod). A total of 75 drop-camera transects unveiled 44,809 organisms belonging to 50 morphotaxa clustered into three distinct faunal assemblages. Fishing locations were represented in two of three assemblages, which were heterogeneous and composed mainly of pebbles, boulders, and rhodolith beds. The unrepresented assemblage was homogeneous and composed entirely of fine sediments. Numerous benthic taxa, potentially sensitive to environmental disturbances, were identified, including tube-dwelling anemones, large sea squirts, erect bryozoans, and extensive rhodolith beds. Insufficient data on benthic species and their associated habitats limit our comprehension of species distributions, abundances, and functional roles in northern waters, creating obstacles for effective self-governance. This research identifies the distribution and structure of benthic habitats in a culturally and economically important region of the Labrador coast, feeding directly into conservation and management strategies for marine habitats in Nunatsiavut facing increasing pressures from climate change.

iKaluk, Inuttitut for Arctic charr (Salvelinus alpinus), holds significant commercial and cultural value for Inuit communities throughout Nunatsiavut. Studies evaluating iKaluk habitat associations in freshwater are plentiful; however, there is limited information on the ecological makeup and sediment characteristics of anadromous charr habitats in marine environments. This study investigated the benthic associations of Arctic charr during their marine residency period in Nain, Nunatsiavut, using underwater videos, harvester-identified fishing locations, and acoustic telemetry. Drop-camera surveys were deployed on previously placed hydrophone acoustic receivers and within harvester-identified fishing locations to describe and quantify available benthic habitats in the study area. Telemetry information was used to identify charr occupancy hotspots, and calculate habitat suitability indices. A total of 248,056 benthic organisms belonging to 63 morphotaxa were identified within the 125 video drops used for benthic community characterization and these represented five faunal assemblages. Marine phase charr occupied estuaries to a greater degree than other fjord or coastal headland environments and these habitats were typically characterized by fine sediments covered by high densities of brittle stars (Ophiuroidea spp.) and benthic diatom mats. The consistent presence of diatomaceous sediments is indicative of abundant foraging opportunities. The importance of these habitats to iKaluk, need to be considered in future marine planning given the cultural and ecological value of this species to many northern communities that face growing threats from environmental change.

Cold-water coral reefs and communities can be locally important calcium carbonate factories in continental shelf and slope environments. Cold-water coral mounds dominated by Desmophyllum pertusum (=Lophelia pertusa) occur within Bay of Biscay submarine canyons. Here we present a late Holocene record of coral carbonate accumulation through a colonial scleractinian coral mound in the 750-850 m depth range in Guilvinec Canyon, northern Bay of Biscay. Guilvinec Canyon, like most submarine canyons of the Bay of Biscay, is a dominantly siliciclastic sandy environment, with occasional coral gardens. Maximum live coral cover in the area surveyed in Guilvinec Canyon was about 9%, measured close to the site of the sediment core analyzed.A 2011 sediment core through the mound recovered 1.18 m of sediment, consisting of mostly siliciclastic silty sand and coral gravel, strongly dominated by Lophelia pertusa fragments. In addition to standard geophysical, grain size, and mineralogical analyses, the core was analyzed by CT-scan. The number of coral calices visible per cm3 was counted, and the core was subsampled for coral calice abundance and mass in 5 mm increments, calculating the number of calices and mass of coral carbonate skeletons per cm3 subsample. An age model from previous 14C and U/Th ages of coral fragments in the core yielded a long-term average coral carbonate accretion rate of 78 g CaCO3 m-2 y-1 over the past ~2150 y, divided into two phases: 40.8 g CaCO3 m-2 y-1 (from core-bottom to -59 cm, approximately 685 ybp), and 156.2 g CaCO3 m-2 y-1 in the upper half of the core. Coarse coral-dominated gravel in the core-catcher contained coral fragments approximately 7 ka in age, indicating a long hiatus before the renewal of coral growth at this site. Aragonite % in the fine sediment was not correlated with coral abundance in the core. A second core recovered nearby was composed of siliciclastic silty sand, but contained almost no coral fragments. The large variation between the two cores indicates high levels of local heterogeneity in sediment accumulation patterns, apparently much greater than the variation in live coral cover at the surface.Coral carbonate accumulation rates in Guilvinec Canyon were 1-2 orders of magnitude lower than coral carbonate accumulation estimates from Lophelia pertusa reefs on the Norwegian Margin. Nonetheless, coral carbonate accumulation rates in the core were an order of magnitude higher than Recent coral carbonate production rates based on ROV-video estimates of coral biomass and published growth rates. This difference may be attributable to time-averaging, local heterogeneity, changes in sedimentation or current regime, or to late-20th century decline in coral abundance resulting from a variety of anthropogenic pressures. Recent threats to Bay of Biscay cold-water coral reefs include increased sediment mobilization from bottom trawling near the heads of submarine canyons, rising seawater temperatures, and declining aragonite saturation. New field and lab experiments on coral growth rates and skeletal degradation may help to disentangle anthropogenic pressures and project the fate of Bay of Biscay cold-water coral reefs in the face of climate change and ocean acidification.

Acanella arbuscula is a common deep-water bamboo coral in the Northwest Atlantic and is considered a Vulnerable Marine Ecosystems indicator. Growth rates and ages of A. arbuscula have not been confirmed, despite the importance of these metrics to understand the species recovery potential when disturbed. One-hundred and fifteen A. arbuscula samples were analyzed to examine the relationship between age, location, and depth, and how environmental conditions influence growth rates. Colonies were collected during scientific trawl or remotely operated vehicle surveys from the SW Grand Banks, Northern Labrador shelf, and SE Baffin shelf from depths of 178-1354 m. Skeletons were cross-sectioned at the proteinaceous nodes and examined under reflected light and fluorescence microscopy to quantify growth rings and determine age and growth rates. The species exhibited both major and minor growth rings. Major growth rings were confirmed to represent annual growth by comparing size metrics and age from a previously bomb-14C dated specimen of A. arbuscula versus specimens aged by growth rings. Minor (sub-annual) growth rings were not consistently observed across specimens and the cause of their formation is unknown. Ages ranged from 8 to 29 years, with radial growth rates of 0.025-0.160 mm/year and axial growth rates of 1.87-16.1 mm/year. Longevity for A. arbuscula is lower than the bamboo coral Keratoisis grayi in the NW Atlantic, but growth rates were consistent with other documented bamboo corals. Multiple regressions revealed that age influenced radial and axial growth rates, with no significant influence of bottom temperature or chlorophyll-a observed for radial growth rates. This study confirms frequency of ring formation in A. arbuscula and that growth rates for the species do not vary significantly based on geographic or bathymetric location.

Cold-water coral reefs and communities can be locally important calcium carbonate factories in continental shelf and slope environments, including submarine canyons. Here we present short-term and long-term estimates of coral carbonate production by colonial scleractinian coral communities in the 750-850 m depth range in Guilvinec Canyon, northern Bay of Biscay. Short-term (annual-decadal) estimates were calculated using local coral skeletal biomass, estimated as a product of coral size and abundance from ROV video surveys, a locally generated species-specific regression between coral colony size and wet weight, and published daily or annual percent growth rates for Lophelia pertusa and Madrepora oculata. A long-term (century-millennial) estimate of carbonate accretion for the same reef was derived from a piston core through the same coral community. Average live colonial scleractinian skeletal biomass in the Guilvinec Canyon coral mounds was 153.9 +/- 39.4 g CaCO3 m(-2). Applying published growth rates, the average annual gross carbonate production was 6.85 +/- 1.79 g CaCO3 m(-2) y(-1), range 0-30.2 g CaCO3 m(-2) y(-1). This carbonate production rate was about one order of magnitude lower than previous estimates from the Norwegian shelf. A 2011 piston core through the mound was analyzed by CT-scan and subsampled for coral abundance. An age model from previous C-14 and U/Th ages of coral fragments in the core yielded a long-term average coral carbonate accretion rate of 78 g CaCO3 m(-2) y(-1) over the past similar to 2150 y, range 40.8 (core-bottom) to 148.5 g CaCO3 m(-2) y(-1) in the upper half, about 1-2 orders of magnitude lower than previous estimates from other regions. Low carbonate accretion rates observed in the Guilvinec Canyon mounds could be attributable to recent declines in live coral cover, indicated by low abundance of live corals in ROV surveys from this site, compared to other regions of the Northeast Atlantic.

Live and sub-fossil deep-sea solitary scleractinian corals (Desmophyllum dianthus) were collected at Orphan Knoll and Flemish Cap, in the southern Labrador Sea (LS), at depths ranging 1600-2200 m, thus encompassing the maximum convection depth of the modern Labrador Sea Water (LSW) and slightly above the modern Northeast Atlantic Deep-Water mass, the two upper components of the North Atlantic Deep Water (NADW). U-series and C-14 ages allowed the assignment of the fossil specimens to the mid-to late Holocene, the Marine Isotope Stages (MIS) 5c, and 7 (likely 7a). The research objective was to document the specificity of the neodymium isotope recordings of water masses occupying the Labrador Sea during these time windows, with special attention to possible convection in this basin, thus to production of the intermediate Labrador Sea Water (LSW). Live-collected specimens and ambient seawater fit with a epsilon Nd value of - 14, assigned to the modern NADW, indicating that the coral skeletons reliably capture the isotopic composition of dissolved Nd. During the midHolocene, they recorded an epsilon Nd-shift from similar to -18 to similar to -14, this latter value since remaining practically unchanged, pointing to a late attainment of modern like conditions in the Labrador Sea. A similar value (similar to-14) was also recorded by a B empty set lling-Aller empty setd pseudo-colony. The MIS 7a specimens yielded a lesser radiogenic value, close to that of the early Holocene (epsilon Nd similar to -18 vs -19), recording the influence of Greenland and Canadian shield lithogenic unradiogenic sources on the open North Atlantic water masses bearing a more radiogenic epsilon Nd-signature. With epsilon Nd-values ranging from -20 to -26, the MIS 5c cluster illustrates a drastically distinct and unstable situation that we associate with sporadically-enhanced overflows of Baffin Bay water and/or the partial dissolution of dolostones linked to hypopycnal sporadic plumes deposited along the Labrador Slope. So far, only the late Holocene and B empty set lling-Aller empty setd corals (eNd similar to -14) point to a modern-like situation with convection down to about 2000 m in the basin, thus LSW production, linked to the advection of more salty and more radiogenic epsilon Nd-bearing North Atlantic water masses, i.e., a full integration of the Labrador Sea into the Atlantic Meridional Overturning Circulation.

Although northern Baffin Bay is recognized as one of the most active seismic zones in Canada, there is limited evidence of Holocene earthquake-triggered mass transport deposits (MTDs) or turbidites in the marine record. Here, we present a record of MTDs and turbidites in two areas of Baffin Bay where earthquakes are the most likely triggering mechanism. Our study focuses on a submarine channel system in Scott Trough (proximal to the Baffin Bay seismic zone – BBSZ) and on MTDs identified from the Home Bay slope, distal to the BBSZ. The channel system in Scott Trough is a sediment-starved relict system from deglaciation, which is now at 200 m water depth, precluding many turbidity current triggers normally associated with active submarine channels. Instead, we propose that the Holocene turbidites in Scott Trough are a result of seismic activity. This hypothesis is further supported by the presence of a turbidite dated at ca 1933 CE resulting from an M 7.4 earthquake. Three other turbidites are recorded in the Scott Trough channel system at ca 9.3, 4.3-3.6 and 2.4 cal ka BP. In Home Bay, two distinct MTDs were dated at just older than 9.1 cal ka BP, which suggests they were triggered by an earthquake during post-glacial, glacio-isostatic adjustment. There is limited evidence for more recent Holocene MTDs in Home Bay, which is consistent with lower seismic activity in the region when compared to Scott Trough. These results provide convincing evidence for a marine record of Holocene earthquakes but should be considered an initial study upon which future Holocene sediment records can be compared.

Ocean warming and Arctic sea-ice decline are expected to affect the biological pump efficiency by altering the timing, quantity, quality, and composition of export production. However, the origins and composition of sinking organic matter are still generally understudied for the oceans, especially in ice-covered areas. Here, we use the compound-specific isotope analysis (CSIA) of amino acids (AAs) to investigate the sources and composition of exported organic matter from a sediment-trap-derived time series of sinking particles collected at depths of 469 and 915 m at the edge of Saglek Bank in the northwestern Labrador Sea from October 2017 to July 2019. The outer edge of Saglek Bank is located at the confluence of cold and fresh Arctic outflow and relatively warmer Atlantic waters. The area is subject to seasonal sea-ice cover and is a biological hotspot for benthic organisms, including deep-sea corals and sponges. Sea ice was present for ∼ 50 % to 60 % of the deployment days in both cycles. Phytoplankton blooms at our study site co-occurred with the onset of sea-ice melt. Microalgal taxonomy indicated the presence of ice-associated diatoms in the sinking particles during the spring bloom in 2018, confirming that sea-ice algae contributed to the organic particle export at our study site. The presence of abundant copepods and copepod nauplii caught in the sediment traps was consistent with a high abundance of copepods in overlying epipelagic waters. Stable carbon isotopes (δ13C) of essential amino acids (EAAs) of the sinking particles revealed a potentially important contribution of sea-ice algae as a carbon source at the base of the food web to sinking particles, with only minor modification by microbial resynthesis. Stable nitrogen isotopes (δ15N) of AAs of sinking particles provided independent evidence of the minor bacterial degradation, and Bayesian mixing models based on normalized δ15N-AA values revealed the dominant contribution of fecal pellets (76 %–96 %) to the sinking particles. Our study demonstrates the importance of sea-ice algae and fecal pellets to the biological pump in the seasonally ice-covered northwestern Labrador Sea, with sea-ice algae exported either directly via passive sinking or indirectly via zooplankton grazing and with fecal pellets dominating the organic particle fluxes.

Deep-sea corals and sponges form ecologically significant habitats that support biodiversity hotspots and contribute to important ecosystem functions such as carbon and nutrient cycling as well as benthic-pelagic coupling. However, quantifying their contributions to ecosystem functioning requires examination not only of the fine spatial distribution of community composition but also community size structure, because larger individuals are expected to contribute more to ecosystem functions than smaller ones. Here we create novel cumulative abundance profiles (CAPs) by combining body size structure with species abundance data to identify ecological drivers of sponge and coral community composition and size structure. Data were collected from 226 drop camera images captured near Saglek Bank, on the northern Labrador shelf and upper slope in the northwest Atlantic. The density of four coral and 17 sponge morphospecies were recorded from each image. The surface area covered by coral and sponge specimens was measured (1458 measurements in total) and converted to size estimates using data from live specimens collected with a rock dredge. Cumulative abundance profiles were then constructed and combined with cluster analysis to identify distinct community assemblages. In addition, distance-based redundancy analysis was used to identify environmental drivers influencing cluster community composition and/or size structure. Finally, organic carbon turnover was calculated for each cluster using published respiration data. Three assemblages were identified with differing composition and size structures. One of these was characterized by large coral and sponge morphospecies and individuals. The spatial distribution of this cluster was controlled by interactions between substrate type, terrain position index (TPI) and orientation of the slope (eastness). When analysing composition or size structure separately, dissolved oxygen and current speed respectively were also identified as key parameters. This finding indicates that substrate type and TPI influence the presence of coral and sponges in the study area, while dissolved oxygen may constrain which morphospecies are present and bottom currents restrict the size of individuals. As predicted, high levels of carbon turnover were driven by large sponge and coral individuals, likely maintained in part by the sponge loop in which sponges recycle dissolved organic matter into particulate organic matter. This study gives the first demonstration of how CAPs can be used to analyse spatial variation in deep-sea benthic community composition and size structure and appropriately quantify contribution to ecosystem functions such as carbon turnover.

Corals and sponges are considered foundational species and can create biodiversity hotspots in the deep sea, yet little is known of their competitive interactions, particularly with respect to resource partitioning among benthic fauna. Here we report on the feeding ecology of deep-water corals, sponges, ascidians, and anemones from a similar to 450 m deep submarine canyon wall off Nova Scotia, Canada. Analysis of bulk stable isotopes of carbon and nitrogen confirms isotopic niche partitioning between species despite their physical proximity. Compound-specific nitrogen isotopes of amino acids (delta N-15-AA) separated the taxa along continua of trophic position and benthic-pelagic coupling and resolve the conspicuously enriched bulk nitrogen patterns commonly observed in sponges. Radiocarbon dating (as Delta C-14) of tissue samples, particulate organic matter (POM) and dissolved inorganic carbon (DIC) from the Scotian Slope sheds light on food provenance and distinguishes diets dominated by older, recalcitrant forms of organic matter versus surface-derived POM. Our results reveal significant differences in resource utilisation among sympatric corals, sponges, ascidians, and anemones and highlight that organisms capable of feeding on more recalcitrant resources will likely play a greater role in supporting deep-water habitats where the quality and flux of fresh POM may be diminished.

Benthic species assemblages are groups of species that co-occur on the seafloor. Linking assemblages to physical environmental features allows for understanding and predicting their spatial distribution. Species identity and abundance are commonly quantified using a taxonomic approach to assess benthic diversity, yet functional traits that describe the behavior, life history, and morphology of a species may be equally or more important. Here, we investigate the biodiversity of five benthic species assemblages in relation to their habitat and environmental conditions in an Ecologically and Biologically Significant Area (EBSA) along Canada’s east coast, using both a taxonomic approach and biological traits analysis. Random Forest regression was applied to map spatial patterns of functional and taxonomic diversity metrics, including richness, Shannon index, and Rao’s quadratic entropy. We evaluate discrepancies between related taxonomic and trait measures, and the community-weighted mean of trait data was calculated to characterize each assemblage. Taxonomic and functional richness – representing the number of species and the species community volume in the trait space, respectively – showed similar spatial patterns. However, when considering diversity, which also accounts for the relative abundance and differences among species or traits, these patterns diverged. Taxonomically different assemblages exhibited similar trait compositions for two assemblages, indicating potential trait equivalencies, while one assemblage exhibited traits potentially indicating sensitivity to human activity. The taxonomic and functional metrics of richness and diversity were low close to the coast, which could be indicative of disturbance. Consideration of functional metrics can support spatial planning and prioritization for management and conservation efforts by assessing the sensitivity of traits to different stressors.

Sustainable coastal social–ecological systems rely on healthy ecosystems known to provide benefits to both nature and people. A key ecosystem found globally is seagrass, for which maps at a scale relevant to inform conservation and management efforts are often missing. Eelgrass (Zostera marina), a species of seagrass found throughout the northern hemisphere, has been declining in Placentia Bay, an ecologically and biologically significant area of Canada’s east coast subject to an increasing human impact. This research provides baseline information on the distribution of eelgrass meadows and their anthropogenic stressors at seven sites of Placentia Bay and three sites of the adjacent Trinity Bay, on the island of Newfoundland. High-resolution maps of eelgrass meadows were created by combining ground-truth underwater videos with unmanned aerial vehicle imagery classified with an object-based image analysis approach. Visual analyses of the imagery and underwater videos were conducted to characterize sites based on the presence of physical disturbances and the semi-quantitative cover of epiphytes, an indication of nutrient enrichment. A total eelgrass area of ~1 km2 was mapped across the 10 sites, with an overall map accuracy of over 80% for 8 of the 10 sites. Results indicated minimum pressures of physical disturbance and eutrophication affecting eelgrass in the region, likely due to the small population size of the communities near the eelgrass meadows. These baseline data will promote the sustainability of potential future coastal development in the region by facilitating the future monitoring and conservation of eelgrass ecosystems.

Many fish species undergo ontogenetic habitat shifts as they grow to fulfill new biological, ecological and environmental requirements. While relationships between fishes and large hard-substrate cold-water corals (CWC) (e.g., Desmophyllum pertusum reefs) have frequently been studied, there are relatively fewer studies examining the relationships of fish with habitats specifically provided by smaller corals (e.g., sea pens) in softbottom environments. Despite this knowledge gap around soft-bottom corals, growing evidence of their importance has nonetheless justified their inclusion as conservation targets in numerous Marine Protected Areas (MPA), including the Canadian Laurentian Channel MPA. Here, we performed ROV and near-seabed drift-camera system surveys within the Laurentian Channel MPA in 2017 and 2018 to assess the influence of fish body size and habitat type on fish small-scale distribution in a low-relief deep-sea soft-sediment environment. We compared the local size structure of the four most abundant deep-sea demersal fish taxa of the channel (Redfish (Sebastes spp.), Witch Flounder (Glyptocephalus cynoglossus), Marlin-Spike Grenadier (Nezumia bairdii) and Longfin Hake (Phycis chesteri)) across one barren and five structural benthic habitats defined by the presence of nine dominant epibenthic invertebrates (actiniarians and CWCs). We used generalized additive models to identify biotic (benthic habitats) and abiotic (depth, bottom types) covariates of size for each taxon. We observed 15,381 fish within the 43.6-ha study area, of which 7,511 fish were measured. Juveniles represented 99% of all fish measured, with a notable increase in average fish size in 2018. While we did not find any associations between benthic habitats and fish life stages, the analysis revealed a significant increase in fish size within sea pen habitats for all four taxa. Conversely, we found a taxon-specific influence of bottom type on fish size for all taxa. In addition, Redfish and Longfin Hake size was positively correlated with depth. For deep-sea demersal fish taxa of the MPA, our results suggest that 1) sea pens provide nursery habitat for early-life stages, 2) fish undergo ontogenetic shifts in microhabitat use and specialization, and 3) fish-habitat associations appear to be facultative rather than obligate. Through the use of in-situ video data, this study provided evidence that small and large fish do not use the same micro-habitats, and that sea pens contribute significantly to fish habitat despite providing less habitat heterogeneity than reef-forming scleractinians or large gorgonians. These results contribute to empirical understanding of fish-habitat relationships at different fish life stages and may inform fisheries management, as well as monitoring efforts in the MPA and other protected deep-sea environments.

Vast amounts of methane (CH4) stored in submarine sediments are susceptible to release in a warming Arctic, further exacerbating climate change in a positive feedback. It is therefore critical to monitor CH4 over pan-regional scales to detect early signs of CH4 release. However, our ability to monitor CH4 is hampered in remote northern regions by sampling and logistical constraints, and few good baseline data exist in many areas. From high-resolution atmospheric CH4 measurements and discrete surface water samples, we estimated instantaneous sea-air CH4 fluxes at various locations. We also created a baseline study of current background levels of CH4 in North Atlantic waters based on the atmospheric CH4 data over 22 d in summer 2021 on a roughly 5100 km voyage in the northern Labrador Sea and Baffin Bay between 55 and 72 degrees N. In addition, we measured CH4 concentrations across the water column at various stations. Measured atmospheric mixing ratios of CH4 ranged from 1944 to 2012 ppbv, with a mean of 1966 +/- 8 ppbv and a baseline of 1954-1981 ppbv. Dissolved CH4 concentrations in the near-surface water peaked at 5.3 nmol L-1 within 1 km down-current of a known cold seep at Scott Inlet and were consistently oversaturated throughout the water column in Southwind Fjord, which is an area that has been recently affected by submarine landslides. Local sea-air CH4 fluxes ranged from 0.003-0.119 mu molm(-2) d(-1), indicating that the ocean released only small amounts of CH4 to the atmosphere at all stations. Atmospheric CH4 levels were also driven by meteorological, spatial, and temporal variations, and both onshore and ocean-based contributions to atmospheric CH4 mixing ratios are likely. Coupled high-resolution measurements of marine and atmospheric CH4 data have the potential to provide ongoing monitoring in a region susceptible to CH4 releases, as well as critical validation data for globalscale measurements and modelling.

In the deep-sea, cold-water corals (CWCs) and other structure-forming fauna locally increase habitat complexity and are host to many fish species. While many studies have focused on hard-bottom CWCs, very little is known about fish associations with soft-bottom CWC habitats. To understand the small-scale linkages between fish, benthic and non-bio-structural habitats in a soft-sediment deep-sea environment, we analysed remotely operated vehicle (ROV) survey videos and recorded the occurrence of fish, invertebrate habitat-forming species and substratum along transects, in the Laurentian Channel Marine Protected Area (MPA) in the Canadian Northwest Atlantic. Almost 13,300 individual fish were recorded, of which all but 65 specimens were identified to family or lower taxonomic rank. The five numerically dominant fish taxa were Redfish (Sebastes spp.), Witch Flounder (Glyptocephalus cynoglossus), Marlin-Spike Grenadier (Nezumia bairdii), Longfin Hake (Phycis chesteri) and one Teleostei morphotype. Teleostei sp1 represents three fish genera (Sandlance (Ammodytes spp.) and two Barracudinas (Arctozenus sp. and Paralepis spp.)) morphologically difficult to differentiate on video footage. Multivariate analysis revealed four habitats based on epibenthic invertebrate densities and diversity. These were dominated by various combinations of sea anemones (Actiniaria), nephtheid soft coral, solitary cup corals (Scleractinia) and three taxa of sea pen (Pennatula spp., Kophobelemnon sp. and Anthoptilum spp.). Univariate analyses performed on dominant fish densities revealed the local influence of hard-bottom substrates and the common influence of soft-sediment micro-features for three fish taxa. All fish densities were correlated with invertebrate density, negatively for Redfish and positively for all other taxa. Our models also predicted the association of four fish taxa with one to two benthic habitats within their preferred depth range. Our results suggest that small-scale habitat heterogeneity in a low relief soft-sediment environment, provided by both physical and biological structures, has a measurable species-specific influence on fish communities. This influence was weaker than typical fish-habitat relationships found in hard-bottom systems, suggesting fish-invertebrate relationships are not obligate. Additionally, we provided evidence that Redfish continue occupying sea pen habitats months after spawning. Our study supports the necessity to continue monitoring the MPA using in-situ video systems to understand the links between fish and habitats in the Laurentian Channel.

Coastal habitats have the potential to be biodiversity hotspots that provide important ecosystem services, but also hotspots for human development and exploitation. Continued use of coastal ecosystem services requires establishing baselines that capture the present state of the benthos. This study employs habitat mapping to establish a baseline describing the spatial distribution of benthic organisms along the western coast of Placentia Bay, an Ecologically and Biologically Significant Area (EBSA) in Newfoundland, Canada. The influence of seafloor characteristics on the distribution of four dominant epifaunal assemblages and two macrophyte species were modelled using two machine learning techniques: the well-established Random Forest and the newer Light Gradient Boosting Machine. When investigating model performance, the inclusion of fine-scale (<1 m) substrate information from the benthic videos was found to consistently improve model accuracy. Predictive maps developed here suggest that the majority of the surveyed areas consisted of a species-rich epifaunal assemblage dominated by ophiuroids, porifera, and hydrozoans, as well as prominent coverage by Agarum clathratum and non-geniculate crustose coralline algae. These maps establish a baseline that enables future monitoring of Placentia Bay’s coastal ecosystem, helping to conserve the biodiversity and ecosystem services this area provides.

Seafloor habitat maps are an important management tool used to delineate distinct regions of the seabed based on their biophysical properties. Spatially continuous bathymetry and backscatter-derived terrain features are commonly used as proxies for environmental conditions and processes that affect species distributions. Multi-scale approaches are increasingly applied to assess the relevant scales at which species co-occur. As the optimal scale(s) may be unknown, features can be calculated at multiple successive scales, yet this results in numerous highly correlated features that may negatively impact model interpretability. To address this increased dimensionality, feature selection approaches can be used to identify the most relevant features. Here, filter and wrapper approaches are assessed to select features from a highly dimensional multi-scale dataset. Terrain features describing the seabed were calculated across ten scales at two coastal sites in Placentia Bay, Newfoundland, Canada. Five species assemblages were identified using ground-truth underwater video sampling. Features predicting the presence of assemblages were assessed using the two selection methods, and the set of chosen features was modelled using three machine learning algorithms: extreme gradient boosting (XGB), random forest (RF), and support vector machines (SVM). The XGB model with features selected by scale-factor from the Boruta wrapper algorithm had the highest accuracy according to cross-validation- (61.67%, kappa 0.49). Bathymetry and terrain attributes were the most important predictors of assemblage occurrence across various analysis scales encompassing both broader and fine-scale variability of the seabed. The proposed feature reduction and selection approach improved the overall accuracy of predictions, and the resulting biological complexity captured in our habitat maps established baseline data for an ecologically significant coastal region.

The Charlie-Gibbs Fracture Zone (CGFZ) is a prominent geological feature offsetting the Mid-Atlantic Ridge (MAR), consisting of two parallel fractures, creating a highly variable seafloor bathymetry. It has been defined as the most important latitudinal biodiversity transitional zone on the MAR. Despite this recognition, the faunal communities living on the fracture zone have not been extensively described. A remotely operated vehicle (ROV) was utilised during the TOSCA (Tectonic Ocean Spreading at the Charlie-Gibbs Fracture Zone) survey. The survey included five ROV video transects at depths between 560 and 2900 m. The objectives of the study were to use this video footage to quantify benthic megafaunal density and biodiversity patterns on the CGFZ and their environmental drivers. Species accumulation curves and generalised additive modelling show that depth and the presence of hard substrates play an important role in explaining species richness and abundance at the CGFZ. Coral taxa showed highest abundance between depths of 1500 and 2000 m, while sponge taxa were more abundant between 1750 and 2250 m. A dense sponge aggregation was identified on a ridge feature at 2250 m depth. The high biodiversity and presence of dense sponge aggregations and coral gardens found in this study highlight the need for detailed surveys to help support decisions made by governing bodies on the protection status of the CGFZ.