Description: This is the first study to present the patterns and environmental controls of benthic biomass size spectra, carbon demand, and production along the entire bathymetric gradient from the shelf to the abyssal depths in the Arctic Ocean. The materials were collected at 17 stations (76 - 5561 m) in the eastern Fram Strait, in the Atlantic passage to the Arctic Ocean, in the vicinity of the productive Marginal Ice Zone, with concentrations of sediment-bound chloroplastic pigments (indicating food availability from phytodetritus sedimentation) higher than in other deep-sea localities at similar depths. Meiobenthic and macrobenthic individuals were measured using image analysis to assess their biovolume, biomass, annual production, and carbon demand. Benthic biomass in the area was clearly higher than that in the High Arctic locations and comparable to that in the lower-latitude North Atlantic. Biomass and annual production were significantly negatively correlated with water depth, with stronger bathymetric clines in macrofauna than in meiofauna and the increasing dominance of meiofauna with increasing depth. A bimodal shape in the size spectra was observed only at the shallow stations, while at depths below 2000 m, an additional trough was present in the macrofaunal part of the spectrum. The entire range of the spectra (i.e., the number of size classes) decreased with increasing depth, especially in the macrofaunal part of the spectrum. Similar slope values in the normalized spectra indicated that the distribution of the biomass across the present size classes was consistent from the shelf to the abyssal depths, irrespective of the decreasing amount of food availability. The fragmented macrofaunal size spectra documented at the two stations were probably due to physical disturbances at the sediment-water interface (e.g., intense bioturbation of holothurians and strong near-bottom currents). Benthic carbon demand declined from 50.7 gC m-2 y-1 at the shelf to 11.5 gC m-2 y-1 at the slope to 2.2 gC m-2 y-1 at the abyssal depths, and its partitioning among meiofauna and macrofauna changed with water depth, with meiofauna contributions increasing from 50 % at the shelf to over 90 % at the deepest station. The estimated total benthic carbon demand exceeded the vertical Corg fluxes, suggesting that the studied system can be particularly sensitive to future changes in productivity regimes and associated organic matter fluxes.

Description: Poliometra prolixa is a common species of comatulid crinoid in the Arctic deep sea. In this study, we characterize the ontogenetic development through the cystidean and pentacrinoid stages, using specimens from the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in Fram Strait, Arctic Ocean. While embryos and early larval stages (e.g., the doliolaria) were not observed, adult P. prolixa were observed on a moored experimental platform at 2500 m water depth, suggesting that P. prolixa larvae do not disperse far from their mothers; doliolaria may have an abbreviated pelagic duration period or may be brooded in this species. The cystidean has a short, translucent stalk with a star-shaped attachment disc and a diamond-shaped translucent head. Metamorphosis from the cystidean to the pentacrinoid is characterized by the formation of brachial ossicles from oral ossicles and by fusion of the basal and radial ossicles to form the calyx. The pentacrinoid stalk is more opaque and develops synarthrial joints first at the distal end. Late pentacrinoids have a xenomorphic stalk, bifurcated arms with pinnules, and cirri. We discuss the niche of Poliometra prolixa and also consider the question of whether cystidean and pentacrinoid stages of comatulid crinoids should be considered larval forms.

Description: Invertebrates in polar and deep-sea environments that have complex life histories are exposed to unique environmental conditions that may favor non-pelagic development and K-strategist reproduction. Although many polar species follow this strategy, the numerically most abundant species tend to have more r-strategist life-history characteristics. We deployed artificial substrata over 3 years in the Arctic deep sea and collected hundreds of specimens of the athecate hydroid Bouillonia cornucopia. While this species has previously been described as rare, we report dense, patchy recruitment on artificial substrata, suggesting that B. cornucopia is highly opportunistic. This species has rapid growth compared to other sessile invertebrates in the study area, high fecundity, and continuous reproduction—all characteristics of an r-selected life history. The species’ gonophores are simple, lacking an obvious spadix or radial canals. We observed nurse cells in histological sections of female gonophores, but no male gonophores were observed. Gonophores break away from the blastostyles in mature specimens and appear to have fertilization envelopes, suggesting that each gonophore is composed of a single oocyte and that embryological evelopment occurs in the water column. Hydroids are typically the first invertebrates to recruit to substrata in the Arctic but are easily overgrown. The opportunistic life histories of B. cornucopia and other hydroids may be adaptive for maintaining populations in the face of high mortality. Our study demonstrates the utility of artificial substrata for collections of otherwise rare opportunistic species.

Description: To overcome the lack of year-long profiling data of upper ocean layers in remote areas, a Subsea Winched Profiling System (SWIPS) was developed at the Alfred Wegener Institute. As a top of a scientific mooring it is able to winch a profiling unit equipped with various sensors from depths up to 200 m to the surface. The whole construction was deliberately designed to be compact and lightweight in order to simplify handling and improve performance in the water. Profiler and winch unit are connected by an electro-mechanical cable, which is used for a communication link between these two components. This allows the position of the profiling unit to be controlled and the measured data to be stored in the winch unit as a safety backup. The cable also supplies the profiling unit with power. Several tests and demonstration deployments have shown the operational readiness of the system.