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: Flatfishes have been the subject of scientific research since the beginning of the 19th century but information on the specific habitat requirement of the adult life stages is largely anecdotal. Detailed knowledge of flatfish habitats however is a precondition for a more ecosystem orientated approach to fisheries management. Here the association between benthic habitat and the adult life stage of three flatfish species plaice (Pleuronectes platessa), sole (Solea solea) and lemon sole (Microstomus kitt) was investigated in the English Channel. Data from groundfish surveys spanning a period of 9 years was used to identify three distinct site groups: sites where a species occurred in consistently high abundances, sites of variable or low abundance and sites at which none were caught. Following the supposition of habitat selection theories such as the ideal free distribution theory these three sites groups should represent a gradient in habitat suitability from highly suitable to less suitable and unsuitable respectively. Habitat parameters and features for the three site groups and species were described and analysed. In particular sediment type and the importance of structuring epifauna for adult flatfish was investigated. Overall plaice and sole showed very similar trends for abiotic environmental parameters such as depth, temperature, salinity and tidal currents. Lemon sole was found over distinctly different habitats which may indicate a stronger niche partitioning of this species. Sediment associations differed between the three species with plaice predominantly occurring over sandy substrates with little mud and gravel content, while sole was found over a wider range of muddy to sandy substrates. Lemon sole was predominantly found over sand however containing a higher percentage of gravel than plaice. Structuring emergent epifauna was related positively to plaice and lemon sole abundances. These structures might be important as they tend to harbour larger numbers of epibenthic species upon which adult plaice and lemon sole prey. No such trend was found for the tactile feeding sole which mainly forages on infaunal polychaetes and molluscs.