Description: The Scotian Shelf harbors unique aggregations of the glass sponge Vazella pourtalesii providing an important habitat for benthic and pelagic fauna. Recent studies have shown that these sponge grounds have persisted in the face of strong inter-annual and multi-decadal variability in temperature and salinity. However, little is known of the environmental characteristics on hourly-seasonal time scales. This study presents the first hydrodynamic observations and associated (food) particle supply mechanisms for the Vazella sponge grounds, highlighting the influence of natural variability in environmental conditions on sponge growth and resilience. Near-bottom environmental conditions were characterized by high temporal resolution data collected with a benthic lander, deployed during a period of 10-months in the Sambro Bank Sponge Conservation Area. The lander was equipped with temperature and oxygen sensors, a current meter, a sediment trap and a video camera. In addition, water column profiles of temperature and salinity were recorded along a transect, conducted in a gradient from high to lower sponge presence probability. Over the course of the lander deployment, temperature fluctuated between 8.8-12 °C with an average of 10.6 °C ± 0.4 °C. The water contained on average 6.3 mg l-1 oxygen and near bottom current speed was on average 0.12 m/s, with peaks up to 0.47 m/s. Semi-diurnal tidal flow was observed to result in constant resuspension of particulate matter in the benthic boundary layer. Surface storm events episodically caused extremely turbid conditions on the seafloor that persisted for several days, with particles being resuspended to more than 13 m above the seabed. The carbon flux in the near-bottom sediment trap peaked during storm events and also after a spring bloom in April, when fresh phytodetritus was observed in the bottom boundary layer. While resuspension events can represent a major stressor for sponges, limiting their filtration capability and remobilizing them, episodes of strong currents and lateral particle transport likely play an important role in food supply and the replenishment of nutrients and oxygen. Our results contextualize human-induced threats such as bottom fishing and climate change by providing more knowledge of the natural environmental conditions under which sponge grounds persist.

Description: The Scotian Shelf harbors unique aggregations of the glass sponge Vazella pourtalesii providing an important habitat for benthic and pelagic fauna. Recent studies have shown that these sponge grounds have persisted in the face of strong inter-annual and multi-decadal variability in temperature and salinity. However, little is known of the environmental characteristics on hourly-seasonal time scales. This study presents the first hydrodynamic observations and associated (food) particle supply mechanisms for the Vazella sponge grounds, highlighting the influence of natural variability in environmental conditions on sponge growth and resilience. Near-bottom environmental conditions were characterized by high temporal resolution data collected with a benthic lander, deployed during a period of 10-months in the Sambro Bank Sponge Conservation Area. The lander was equipped with temperature and oxygen sensors, a current meter, a sediment trap and a video camera. In addition, water column profiles of temperature and salinity were recorded along a transect, conducted in a gradient from high to lower sponge presence probability. Over the course of the lander deployment, temperature fluctuated between 8.8-12 °C with an average of 10.6 °C ± 0.4 °C. The water contained on average 6.3 mg/l oxygen and near bottom current speed was on average 0.12 m/s, with peaks up to 0.47 m/s. Semi-diurnal tidal flow was observed to result in constant resuspension of particulate matter in the benthic boundary layer. Surface storm events episodically caused extremely turbid conditions on the seafloor that persisted for several days, with particles being resuspended to more than 13 m above the seabed. The carbon flux in the near-bottom sediment trap peaked during storm events and also after a spring bloom in April, when fresh phytodetritus was observed in the bottom boundary layer. While resuspension events can represent a major stressor for sponges, limiting their filtration capability and remobilizing them, episodes of strong currents and lateral particle transport likely play an important role in food supply and the replenishment of nutrients and oxygen. Our results contextualize human-induced threats such as bottom fishing and climate change by providing more knowledge of the natural environmental conditions under which sponge grounds persist.

Description: The Scotian Shelf harbors unique aggregations of the glass sponge Vazella pourtalesii providing an important habitat for benthic and pelagic fauna. Recent studies have shown that these sponge grounds have persisted in the face of strong inter-annual and multi-decadal variability in temperature and salinity. However, little is known of the environmental characteristics on hourly-seasonal time scales. This study presents the first hydrodynamic observations and associated (food) particle supply mechanisms for the Vazella sponge grounds, highlighting the influence of natural variability in environmental conditions on sponge growth and resilience. Near-bottom environmental conditions were characterized by high temporal resolution data collected with a benthic lander, deployed during a period of 10-months in the Sambro Bank Sponge Conservation Area. The lander was equipped with temperature and oxygen sensors, a current meter, a sediment trap and a video camera. In addition, water column profiles of temperature and salinity were recorded along a transect, conducted in a gradient from high to lower sponge presence probability. Over the course of the lander deployment, temperature fluctuated between 8.8-12 °C with an average of 10.6 °C ± 0.4 °C. The water contained on average 6.3 mg l-1 oxygen and near bottom current speed was on average 0.12 m/s, with peaks up to 0.47 m/s. Semi-diurnal tidal flow was observed to result in constant resuspension of particulate matter in the benthic boundary layer. Surface storm events episodically caused extremely turbid conditions on the seafloor that persisted for several days, with particles being resuspended to more than 13 m above the seabed. The carbon flux in the near-bottom sediment trap peaked during storm events and also after a spring bloom in April, when fresh phytodetritus was observed in the bottom boundary layer. While resuspension events can represent a major stressor for sponges, limiting their filtration capability and remobilizing them, episodes of strong currents and lateral particle transport likely play an important role in food supply and the replenishment of nutrients and oxygen. Our results contextualize human-induced threats such as bottom fishing and climate change by providing more knowledge of the natural environmental conditions under which sponge grounds persist.

Description: Seamounts represent ideal systems to study the influence and interdependency of environmental gradients at a single geographic location. These topographic features represent a prominent habitat for various forms of life, including microbiota and macrobiota, spanning benthic as well as pelagic organisms. While it is known that seamounts are globally abundant structures, it still remains unclear how and to which extend the complexity of the seafloor is intertwined with the local oceanographic mosaic, biogeochemistry and microbiology of a seamount ecosystem. Along these lines, the present study aimed to explore whether and to which extend seamounts can have an imprint on the microbial community composition of seawater and of sessile benthic invertebrates, sponges. For our high-resolution sampling approach of microbial diversity (16S rRNA gene Amplicon sequencing) along with measurements of inorganic nutrients and other biogeochemical parameters, we focused on the Schulz Bank seamount ecosystem, a sponge ground ecosystem which is located on the Arctic Mid-Ocean Ridge. Seawater samples were collected at two sampling depths (mid-water: MW, and near-bed water: BW) from a total of 19 sampling sites. With a clustering approach we defined microbial micro-habitats within the pelagic realm at Schulz Bank, which were mapped onto the seamount's topography, and related to various environmental parameters (such as suspended particulate matter (SPM), dissolved inorganic carbon (DIC), silicate (SiO4−), phosphate (PO43−), ammonia (NH4+), nitrate (NO32−), nitrite (NO2), depth, and dissolved oxygen (O2)). The results of our study reveal a seamount effect (sensu stricto) on the microbial mid-water pelagic community up to approximately 200 m above the seafloor. Further, we observed a strong spatial heterogeneity in the pelagic microbial landscape across the seamount, with planktonic microbial communities reflecting oscillatory and circulatory water movements, as well as processes of bentho-pelagic coupling. Depth, NO32−, SiO4−, and O2 concentrations differed significantly between the determined pelagic microbial clusters close to the seafloor (BW), suggesting that these parameters were presumably linked to changes in microbial community structures. Secondly, we assessed the associated microbial community compositions of three sponge species along a depth gradient of the seamount. While sponge-associated microbial communities were found to be mainly species-specific, we also detected significant intra-specific differences between individuals, depending on the pelagic near-bed cluster they originated from. The variable microbial phyla (i.e. phyla which showed significant differences across varying depth, NO32−, SiO4−, O2 concentrations and different from local seawater communities) were distinct for every sponge-species when considering average abundances per species. Variable microbial phyla included representatives of both, those taxa traditionally counted to the variable community fraction, as well as taxa counted traditionally to the core community fraction. Microbial co-occurrence patterns for the three examined sponge species Geodia hentscheli (demosponge, HMA), Lissodendoryx complicata (demosponge, most likely LMA), and Schaudinnia rosea (Hexactinellida, most likely LMA) were distinct from each other. Over all, this study shows that topographic structures such as the Schulz Bank seamount can have an imprint (seamount effect sensu lato) on both, the microbial community composition of seawater and of sessile benthic invertebrates such as sponges by an interplay between the geology, physical oceanography, biogeochemistry and microbiology of seamounts.

Description: Deep-sea sponge grounds are hotspots of benthic biomass and diversity. To date, very limited data exists on the range of environmental conditions in areas containing deep-sea sponge grounds and which factors are driving their distribution and sustenance. We investigated oceanographic conditions at a deep-sea sponge ground located on an Arctic Mid-Ocean Ridge seamount. Hydrodynamic measurements were performed along CTD transects and a lander was deployed within the sponge ground that recorded near-bottom physical properties as well as vertical fluxes of organic matter over an annual cycle. The data demonstrate that the sponge ground is found at water temperatures of -0.5 to 1 °C and is situated at the interface between two water masses at only 0.7° equatorward of the turning point latitude of semidiurnal lunar internal tides. Internal waves supported by vertical density stratification interact with the seamount topography and produce turbulent mixing as well as resuspension of organic matter with temporarily very high current speeds up to 0.72 m s-1. The vertical movement of the water column delivers food and nutrients from water layers above and below towards the sponge ground. Highest organic carbon flux was observed during the summer phytoplankton bloom period, providing fresh organic matter from the surface. The flux of fresh organic matter is unlikely to sustain the carbon demand of this ecosystem. Therefore, the availability of bacteria, nutrients and dissolved and particulate matter, delivered by tidally-forced internal wave turbulence and transport by horizontal mean flows, likely plays an important role in meeting ecosystem-level food requirements.

Description: Deep-sea sponge grounds are hotspots of benthic biomass and diversity. To date, very limited data exists on the range of environmental conditions in areas containing deep-sea sponge grounds and which factors are driving their distribution and sustenance. We investigated oceanographic conditions at a deep-sea sponge ground located on an Arctic Mid-Ocean Ridge seamount. Hydrodynamic measurements were performed along CTD transects and a lander was deployed within the sponge ground that recorded near-bottom physical properties as well as vertical fluxes of organic matter over an annual cycle. The data demonstrate that the sponge ground is found at water temperatures of -0.5 to 1 °C and is situated at the interface between two water masses at only 0.7° equatorward of the turning point latitude of semidiurnal lunar internal tides. Internal waves supported by vertical density stratification interact with the seamount topography and produce turbulent mixing as well as resuspension of organic matter with temporarily very high current speeds up to 0.72 m s-1. The vertical movement of the water column delivers food and nutrients from water layers above and below towards the sponge ground. Highest organic carbon flux was observed during the summer phytoplankton bloom period, providing fresh organic matter from the surface. The flux of fresh organic matter is unlikely to sustain the carbon demand of this ecosystem. Therefore, the availability of bacteria, nutrients and dissolved and particulate matter, delivered by tidally-forced internal wave turbulence and transport by horizontal mean flows, likely plays an important role in meeting ecosystem-level food requirements.

Description: The genus Sebastes is a morphologically and ecologically diverse genus of rockfish characterized by high longevity, late-maturity, and low natural mortality. On the northwest Atlantic continental shelf, the Acadian redfish (Sebastes fasciatus) is the most common rockfish species above 300 m depth. This species has been widely exploited resulting in the depletion or collapse of most of its stocks. Management of long-lived species with intricate life-history characteristics is challenging and requires highly integrated biological and oceanographic monitoring, which allow the identification of environmental drivers and demographic and behavioural trends. The present study uses high temporal resolution imaging and environmental data, acquired with an autonomous lander deployed for 10-months at the Sambro Bank Sponge Conservation Area (Scotian Shelf) to elucidate S. fasciatus temporal dynamics and behavioural trends in response to near-bed environmental conditions. S. fasciatus, mostly displayed passive locomotion and static behaviours, in common with other shelf-dwelling Sebastes species. Hydrodynamics appear to act as a synchronizing factor conditioning its swimming behaviour. S. fasciatus total counts exhibited a seasonal shift in rhythm's phase likely reflecting changes in lifestyle requirements.