Rare earth and trace elements in deep-sea sponges of the North Atlantic.

The available data on trace elements (TE) of deep-sea organisms is scarce and nonexistent for rare earth elements (REE). Hence, this study characterizes REE and TE in five porifera genera (Jaspis, Geodia, Hamacantha, Leiodermatium, Poliopogon) collected in deep-sea areas (between 481 and 2656 m) of the North Atlantic. Aluminium was the most common TE while lead was the less abundant. These sponges showed an increased accumulation of TE compared with other probably influenced by volcanic activity. Poliopogon amadou sampled at the deepest location presented the highest concentration of all REE. All studied species exhibited a Light REE enrichment in comparison to Heavy REE and showed a negative Ce anomaly with a less conspicuous Eu depletion. Besides the establishment of a baseline for future comparisons, this study provides the first record of REE in a sessile deep-sea marine invertebrate group.

Dense cold-water coral garden of Paragorgia johnsoni suggests the importance of the Mid-Atlantic Ridge for deep-sea biodiversity.

Mid-ocean ridges generate a myriad of physical oceanographic processes that favor the supply of food and nutrients to suspension- and filter-feeding organisms, such as cold-water corals and deep-sea sponges. However, the pioneering work conducted along the Mid-Atlantic Ridge failed to report the presence of large and dense living coral reefs, coral gardens, or sponge aggregations. Here, we describe the densest, near-natural, and novel octocoral garden composed of large red and white colonies of Paragorgia johnsoni Gray, 1862 discovered at 545-595 m depth on the slopes of the Mid-Atlantic Ridge, in the Azores region. This newly discovered octocoral garden is a good candidate for protection since it fits many of the FAO criteria that define what constitutes a Vulnerable Marine Ecosystem. The observations described here corroborate the existence of a close relationship between the octocoral structure and the ambient currents on ridge-like topographies, providing new insights into the functioning of mid-ocean ridges' ecosystems. The ubiquitous presence of biogenic and geological topographies associated with mid-ocean ridges, which could act as climate refugia, suggests their global importance for deep-sea biodiversity. A better understanding of the processes involved is, therefore, required. Our observations may inspire future deep-sea research initiatives to narrow existing knowledge gaps of biophysical connections with benthic fauna at small spatial scales along mid-ocean ridges.

Area Estimation of Deep-Sea Surfaces from Oblique Still Images.

Estimating the area of seabed surfaces from pictures or videos is an important problem in seafloor surveys. This task is complex to achieve with moving platforms such as submersibles, towed or remotely operated vehicles (ROV), where the recording camera is typically not static and provides an oblique view of the seafloor. A new method for obtaining seabed surface area estimates is presented here, using the classical set up of two laser devices fixed to the ROV frame projecting two parallel lines over the seabed. By combining lengths measured directly from the image containing the laser lines, the area of seabed surfaces is estimated, as well as the camera's distance to the seabed, pan and tilt angles. The only parameters required are the distance between the parallel laser lines and the camera's horizontal and vertical angles of view. The method was validated with a controlled in situ experiment using a deep-sea ROV, yielding an area estimate error of 1.5%. Further applications and generalizations of the method are discussed, with emphasis on deep-sea applications.

Marine litter distribution and density in European seas, from the shelves to deep basins.

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.