This Week in the Deep

New and noteworthy publications in deep-sea science for the week of December 31st, 2012.

PLoS One: How Deep-Sea Wood Falls Sustain Chemosynthetic Life

Large organic food falls to the deep sea – such as whale carcasses and wood logs – are known to serve as stepping stones for the dispersal of highly adapted chemosynthetic organisms inhabiting hot vents and cold seeps. Here we investigated the biogeochemical and microbiological processes leading to the development of sulfidic niches by deploying wood colonization experiments at a depth of 1690 m in the Eastern Mediterranean for one year. Wood-boring bivalves of the genus Xylophaga played a key role in the degradation of the wood logs, facilitating the development of anoxic zones and anaerobic microbial processes such as sulfate reduction. Fauna and bacteria associated with the wood included types reported from other deep-sea habitats including chemosynthetic ecosystems, confirming the potential role of large organic food falls as biodiversity hot spots and stepping stones for vent and seep communities. Specific bacterial communities developed on and around the wood falls within one year and were distinct from freshly submerged wood and background sediments. These included sulfate-reducing and cellulolytic bacterial taxa, which are likely to play an important role in the utilization of wood by chemosynthetic life and other deep-sea animals

Journal of Experimental Marine Biology and Ecology: Effect of a physical disturbance event on deep-sea nematode community structure and ecosystem function

Numerous studies have been conducted on the effect of physical disturbance on shallow water benthic communities, but there is a paucity of data from deep-sea environments. We conducted a laboratory experiment using undisturbed sediment cores from Chatham Rise (water depth = 345 m), Southwest Pacific, to investigate the effects of a physical disturbance event (resuspension of surface sediments) on sediment characteristics (sediment grain size, pigment content), nematode community attributes (abundance, diversity, community structure) and ecosystem function (sediment community oxygen consumption (SCOC)) over a period of 9 days. Disturbance did not have any noticeable impact on sediment characteristics, SCOC, or nematode species richness, but led to changes in vertical distribution patterns and shifts in nematode community structure. The magnitude of disturbance-related effects was, however, much smaller than the effect of sediment depth (0–1, 1–3, and 3–5 cm), and the main impact of disturbance on nematode vertical distribution patterns and community structure appeared to be related to a vertical re-shuffling of nematodes in the sediments rather than mortality. We did not observe substantial increases in the abundance of nematode genera generally regarded as disturbance-tolerant, such as Sabatieria. The worst-affected species belongs to the Stilbonematinae, a group of typically long and slender nematodes that may be easily damaged by physical disturbance. The limited impact of physical disturbance on benthic community structure and function suggests that the Chatham Rise nematode community is relatively resilient to sediment resuspension. This resilience may have arisen from frequent exposure to disturbance in the field (e.g., from strong currents), or may be a more widespread feature of nematode communities.

Systematics and Biodiversity: Molecular taxonomy reveals broad trans-oceanic distributions and high species diversity of deep-sea clams (Bivalvia: Vesicomyidae: Pliocardiinae) in chemosynthetic environments

Large vesicomyid clams are common inhabitants of sulphidic deep-sea habitats such as hydrothermal vents, hydrocarbon seeps and whale-falls. Yet, the species- and genus-level taxonomy of these diverse clams has been unstable due to insufficiencies in sampling and absence of detailed taxonomic studies that would consistently compare molecular and morphological characters. To clarify uncertainties about species-level assignments, we examined DNA sequences from mitochondrial cytochrome-c-oxidase subunit I (COI) in conjunction with morphological characters. New and published COI sequences were used to create a molecular database for 44 unique evolutionary lineages corresponding to species. Overall, the congruence between molecular and morphological characters was good. Several discrepancies due to synonymous species designations were recognized, and acceptable species names were rectified with published COI sequences in cases where morphological specimens were available. We identified seven species with trans-Pacific distributions, and two species with Indo-Pacific distributions. Presently, 27 species have only been documented from one region, which might reflect limited ranges, or insufficient geographical sampling. Vesicomyids exhibit the greatest species diversity along the northwest Pacific ridge systems and in the eastern Pacific, along the western America margin, where depth zonation typically results in segregation of closely related species. The broad distributions of several vesicomyid species suggest that their required chemosynthetic habitats might be more common than previously recognized and occur along most continental margins.

BBC: Prospects for underwater goldmine in Pacific decline

A London-listed company’s plans to create the world’s first underwater goldmine on the Pacific seabed have hit the rocks.