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Determining the lipid content and fatty acid (FA) composition of aquatic organisms has been of major interest in trophic ecology, aquaculture, and nutrition for over half a century. Although protocols for lipid analysis are well-described, their application to aquatic sciences often requires modifications to adapt to field conditions and to sample type. Here, we present the current state of knowledge of methods dedicated to both marine and freshwater lipid analyses, from sampling to data treatment. We review: (i) sample preservation, storage and transport protocols, and their effects on lipids, (ii) lipid extraction, separation of polar and neutral lipids, derivatization, and detection methods, and (iii) available tools for the statistical analysis of FA data. We provide recommendations for best practices in field situations and advocate for protocol standardization and interlaboratory calibration.

The Whittard Canyon (NE Atlantic) is one of the largest canyon systems on the northern Bay of Biscay margin. It likely receives a high input of organic matter from the productive overlying surface waters, and part of this organic matter may eventually be transferred down the canyon into the Whittard Channel extending from the canyon mouth onto the Biscay Abyssal Plain. To establish if substantial transport of organic matter takes place from the canyon into the deep-sea channel we: (1) deployed a benthic lander in the Whittard Channel for a period of one year to measure near-bottom particulate matter transport and deposition rates; (2) collected surface sediment samples from the Whittard Channel and adjacent areas to assess possible organic matter enrichment in the channel (3) surveyed transects across the channel and adjacent areas with towed video camera to assess distribution of benthic megafauna potentially indicating enhanced flux of fresh organic material. The video surveys revealed massive occurrence of elpidiid holothurians in the proximal Whittard Channel, whilst only low numbers were counted further down the channel and on areas adjacent to the channel. We speculate that these deposit-feeding holothurians were attracted by the elevated content of relatively fresh organic matter in surface sediments of the proximal channel, as indicated by analysis of the surface sediment samples. Yet, whilst we expected that organic matter enrichment in the channel could be attributed to down-canyon transport through the Whittard Canyon, this could not be confirmed by data recorded by the benthic lander. During most of the 1-year deployment period, the net near-bottom currents and suspended particulate matter transport was directed in up-channel direction. During two sediment-gravity flow events recorded in March and July 2011, most likely originating from the Whittard Canyon, substantial deposition of particulate matter did occur in the Whittard Channel. However, the mater

Discussing submarine canyons dynamics through a multidisciplinary approach allowed to identify both advances in knowledge and remaining gaps concerning the controlling factors underlying the formation, development, ecological functioning and vulnerability of canyons at various time scales. As a result, we identified a number of recommendations for future research and actions that the interested reader will discover in this synthetic chapter, drafted as a collective effort in the months following our meeting. The subsequent chapters, each written by a workshop participant, detail the specificities and dynamics of of submarine canyons within and beyond the Mediterranean domain.

Anthropogenic litter is present in all marine habitats, from beaches to the most remote points in the oceans. On the seafloor, marine litter, particularly plastic, can accumulate in high densities with deleterious consequences for its inhabitants. Yet, because of the high cost involved with sampling the seafloor, no large-scale assessment of distribution patterns was available to date. Here, we present data on litter distribution and density collected during 588 video and trawl surveys across 32 sites in European waters. We found litter to be present in the deepest areas and at locations as remote from land as the Charlie-Gibbs Fracture Zone across the Mid-Atlantic Ridge. The highest litter density occurs in submarine canyons, whilst the lowest density can be found on continental shelves and on ocean ridges. Plastic was the most prevalent litter item found on the seafloor. Litter from fishing activities (derelict fishing lines and nets) was particularly common on seamounts, banks, mounds and ocean ridges. Our results highlight the extent of the problem and the need for action to prevent increasing accumulation of litter in marine environments.

The macrofaunal assemblages from three Portuguese submarine canyons, Nazare, Cascais and Setubal were studied from samples collected at their upper (900-1000 m), middle (3200-3500 m) and lower sections (4200-4500 m) and at the adjacent open slopes (similar to 1000 m), during the HERMES cruises D297 (R.R.S. Discovery, 2005) CD179 (R.R.S. Charles Darwin, 2006) and 64PE252 (R.V. Pelagia, 2006). The taxonomic composition and patterns in biodiversity, abundance and community structure of the benthic macrofauna were described. Annelida (42.1% of total abundance; 137 species) and Arthropoda (20.6%; 162 species) were, respectively, the most abundant and the most species-rich Phyla among the 342 taxa identified during this study. Multivariate analyses showed significant differences between and within canyons and between canyons and open slope assemblages. At their upper section, canyons supported higher macrofauna abundance but slightly lower biodiversity than the adjacent slopes at similar depth. In all canyons abundance reached the highest value in the middle section and the lowest in the upper section, with marked fluctuations in Nazare (474-4599 ind. m(-2)) and lower variability in Cascais (583-1125 ind. m(-2)). The high abundance and dominance of the assemblages in the middle section of Nazare and Setubal was accompanied by depressed biodiversity, while in Cascais, Hurlbert's expected species richness showed increasing values from the upper to the middle canyon, and maintained the high values at the lower section. Overall, the Nazare Canyon showed the lowest expected species richness (ES(100): 16-39) and the Cascais Canyon the highest (39-54). There was a significant negative Kendall's correlation between total organic carbon concentrations in the superficial sediments and ES(100) and a significant positive correlation between total nitrogen and macrofauna density. The influences of organic enrichment, sediment heterogeneity and hydrodynamic regime on the abundance, div

Megafaunal organisms play a key role in ecosystem functioning in the deep-sea through bioturbation, bioirrigation and organic matter cycling. At 3500 m water depth in the Nazaré Canyon, NE Atlantic, very high abundances of the infaunal holothurian Molpadia musculus were observed. To quantify the role of M. musculus in sediment cycling, sediment samples and holothurians were collected using an ROV and in situ experiments were conducted with incubation chambers. The biochemical composition of the sediment (in terms of proteins, carbohydrates and lipids), the holothurians' gut contents and holothurians' faecal material were analysed. In the sediments, proteins were the dominant organic compound, followed by carbohydrates and lipids. In the holothurian's gut contents, protein concentrations were higher than the other compounds, decreasing significantly as the material passed through the digestive tract. Approximately 33±1% of the proteins were digested by the time sediment reached the mid gut, with a total digestion rate equal to 67±1%. Carbohydrates and lipids were ingested in smaller amounts and digested with lower efficiencies (23±11% and 50±11%, respectively). As a result, the biopolymeric C digestion rate was on average 62±3%. We estimated that the population of M. musculus could remove approximately 0.49±0.13 g biopolymeric C and 0.13±0.03 g N m−2 d−1 from the sediments. These results suggest that M. musculus plays a key role in the benthic tropho-dynamics and biogeochemical processes in the Nazaré Canyon.

A sharp regime shift from a brittle star Amphiura filiformis dominated state to a burrowing mud shrimp Callianassa subterranea dominated situation was observed in a region of the North Sea known as the Frisian Front in the mid-1990s. No indications exist that food levels or other relevant conditions in this part of the North Sea had changed significantly. However, the new state has persisted until the present. This could suggest that this regime shift represents a transition between alternative stable community states. We propose a potential explanation for the existence of 2 stable states, which agrees with experimental and field observations. We demonstrated experimentally that sediments inhabited by burrowing shrimps are more susceptible to sediment resuspension by tidal currents and wave forces than sediments inhabited by brittle stars. Although the burrowing shrimps apparently thrive under these conditions, successful recruitment of brittle stars may be hampered on such unstable frequently resuspended sediments. This implies a positive feedback; brittle stars promote sediment stability, which favors their persistence. We created a model to demonstrate that this feedback between the benthic community and sediment stability may cause both the shrimp dominated state and the brittle star dominated state to be stable under the same external conditions.