Description: In this paper, we present two innovative optical systems dedicated to deep sea observation. The instrumentation and associated methodology are developed in the context of European project EXOCET/D (FP6-GOCE-CT-2003-505342, http://w3.ifremer.fr/exocetd) [SAR04]. The general objective of the project focuses on the design, the implementation and the test of specific instruments to explore, study and quantify biodiversity in the deep sea. The relationship between habitats and environmental dynamics is also an important issue of the project. The presented development takes benefit of work carried out at Ifremer for several years in the field of underwater imaging and measurement [CAD04].One specific target is to set up a complete methodology to make a 3D reconstruction of small scale scenes using stereovision techniques. To meet this scientific requirement, a new system, called IRIS (Invariant 3D Reconstruction by Instrumented Stereovision), has been specified and is under development. It includes the design of a stereovision head and the associated methods for data processing.For an operational use in an underwater environment, the stereovision head will be operated by Ifremers deep scientific Remotely Operated Vehicle victor 6000. The ROV is landed on the seafloor to keep a fixed and stable attitude, a small region of interest (around 1m3) is investigated by the stereovision rig mounted at the tip of victor 6000s instrumented robotic arm MAESTRO.

Description: In 1999, the AWI deep-sea research group established the first and only long-term deep-sea observatory beyond the polar circle, 'Hausgarten' (see Soltwedel et al.). Footage from underwater camera transects has shown that demersal fish largely belonging to the eelpout family (Zoarcidae) constitute an important fraction of the benthic fauna. Despite their numerical abundance, little is known about their biology and functional ecological role.Here, we used baited traps and trawls to sample the demersal ichthyofauna at six stations that constitute the shallower end of the Hausgarten depth transect (1200-3200m). Stomach contents analysis showed that trawled eelpout chiefly fed on small crustaceans (cumaceans, amphipods, isopods) and polychaetes whereas trap-caught fish fed largely on scavenging amphipods.Results from radio stable isotope analysis indicate that starfish (Hymenaster pellucidus, Poraniomorpha cf. tumida, Bathybiaster vexillifer) followed by scavenging amphipods (Eurythenes gryllus) occupied the highest trophic level at most stations (δ15N 11.9-24.6). Fish had an intermediate trophic position (Lycodes spp. δ15N 12.8-13.7), reflecting their preference for macrofaunal invertebrates. The lowest trophic level at different stations was occupied by various taxonomic groups due to differences in the composition of species sampled. Assuming a stepwise δ15N enrichment of 3.8 per trophic level, the benthic food web sampled at stations along the depth gradient ranged from four to six trophic levels. This large figure may be indicative of a complex food web structure caused by intense recycling of nutrients which is characteristic for food-limited deep-sea environments. Food limitation may be even stronger at high latitudes due to reduced primary productivity caused by seasonal ice coverage.

Description: Deep-sea research is expensive and depends heavily on technological progress much in the same way as the exploration of space. In addition, the reduced size of extreme or punctual deep-sea ecosystems make them difficult to study with conventional instrumentations deployed from surface vessels as it is done in sedimentary ecosystems.In 2004, the European Commission therefore funded a three-year project, EXOCET/D, to develop, implement and test specific instruments aimed at exploring, describing, quantifying and monitoring biodiversity in deep-sea fragmented habitats as well as at identifying links between community structure and environmental dynamics. Another objective is to develop novel data integration tools and to improve payload inter-operability. EXOCET/D involves partners from ten European research institutions and three small and medium enterprises.Here, we present the programme of the seven work packages. The working fields include: video and acoustic imagery, _in situ_ analysis of physico-chemical factors, quantitative sampling of macro- and micro-organisms, _in vivo_ experiments, integration of multidisciplinary data and implementation on European submersibles. Experimental devices onboard will complement the approach, enabling experiments on species physiology. In August 2006, the project will go into a final phase of technical and scientific field validation during the MoMARETO cruise to the Azores Triple Junction.

Description: Large-scale spatial surveys of fish species in relation to habitat have tended to focus on depth, sediment type and temperature as descriptors of fish habitats. At a smaller scale, habitat parameters such as the relief of the sea floor, the presence of structuring fauna and prey availability may have a large influence on fish distribution, but often are not considered. In the present study we used video survey techniques to study habitat components in areas of the English Channel that were known to support consistently high densities of adult plaice. Habitat features were quantified and related to the density of adult plaice caught within the same study areas. To focus the study on habitat components other than sediment type all sites chosen had sandy substrata. The scale and spatial distribution and heterogeneity of physical and biological structures were quantified for each site and correlated to plaice densities. Plaice densities correlated with the abundance of benthic fauna recorded. In particular the emergent tube-dwelling polychaetes Lanice conchilega and Cheatopterus spp., that are a valuable food source for plaice dominated some sites. Abiotic habitat features and habitat heterogeneity showed no clear relationships with respect to plaice densities at the scale of our surveys. This indicated that prey availability might be the driving force for habitat selection of adult plaice within sandy habitats and that other habitat descriptors assume lesser importance at smaller spatial scales.

Description: The deep sea represents the largest ecosystem on earth. Due to its enormous dimensions and inaccessibility, the deep-sea realm is the worlds least known habitat. To understand ecological ties, the assessment of temporal variabilities is essential. Only long-term investigations at selected sites, describing seasonal and interannual variations, can help to identify changes in environmental settings determining the structure, the complexity, and the development of deep-sea communities. The opportunity to measure processes at sufficient time scales will also help to differentiate between natural variabilities and environmental changes due to anthropogenic impacts.High latitudes are amongst the most sensitive environments in respect to climate change, a fact urgently demanding the assessment of time-series in Polar Regions. The deep-sea long-term station Hausgarten of the Alfred Wegener Institute for Polar and Marine Research, Germany, was established in summer 1999 in the eastern Fram Strait off Spitsbergen. Beside a central experimental area at 2500 m water depth, we defined 9 stations along a depth transect between 1000-5500 m, and additional 6 stations along a latitudinal transect crossing the central Hausgarten station, which will be revisited yearly to analyse seasonal and interannual variations in biological, geochemical and sedimentological parameters.Moorings carrying current meters and sedimentation traps are used to assess hydrographic conditions in the area and to characterise and quantify organic matter fluxes to the seafloor. The exchange of solutes between the sediments and the overlaying waters are studied to investigate major processes at the sediment-water-interface. Vertical gradients of nutrients, organic carbon contents, C/N ratios, porosity and other geochemical parameters are determined to characterize the geochemical milieu of the upper sediment layers. Biogenic sediment compounds are analysed to estimate activities and total biomass of the smallest sediment-inhabiting organisms. The quantification of benthic organisms from bacteria to megafauna is a major goal in biological investigations.