How Deep-Sea Wood Falls Sustain Chemosynthetic Life

Abstract

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.

Ecological succession leads to chemosynthesis in mats colonizing wood in sea water

“…to convert the refractory wood carbon into labile organic matter (Voight, 2015). New fermentative niches can be created within macrofaunal feces (Purchon, 1941;Fagervold et al, 2014) that could result in high hydrogen sulfide concentration after 1 year (Bienhold et al, 2013). These environmental chemical conditions are similar to the ones found in other deep-sea sulfidic habitats where microbial mats colonize exposed surfaces.…”

“…The proportion of dsr and apr genes increased at the end of the experiment supporting the hypothesis of the presence of sulfate-reducing Desulfovibrio-related bacteria (Otu3), which quickly dominated the wood mat community. The common presence of Desulfovibrio in wood falls (Bienhold et al, 2013;Fagervold et al, 2013;Pradel et al, 2013;Kalenitchenko et al, 2015) and measures of hydrogen sulfide pulses on wood surfaces after 1 month (Yücel et al, 2013;Kalenitchenko et al, 2015) suggests the importance of this genera for the production of hydrogen sulfide from wood falls. In addition, the bacterial community's potential to use hydrogen sulfide as electron donor was confirmed by the detection of the sulfur oxidation protein coding gene soxB.…”

Characteristics of meiofauna in extreme marine ecosystems: a review

“…Bones are then colonised by microorganisms or chemoautotrophs using sulphur as respiratory metabolites (Smith and Baco 2003;Fujiwara et al 2007), as well as by specialised bone-eating polychaetes of the genus Osedax (Rouse et al 2004) and, finally, by suspension feeders. Sunken wood is widely distributed in the oceans and constitutes a microhabitat suitable for sulphide-oxidising symbioses due to the sulphides produced from the decomposition of the wood in seawater (Laurent et al 2009;Bienhold et al 2013). …”

Paleocene methane seep and wood-fall marine environments from Spitsbergen, Svalbard

“…The large surface area of wood chips was likely a favourable substrate for the development of wood-degrading bacteria, which could contribute to the formation of sulphide (e.g. Bienhold et al, 2013;Fagervold et al, 2014). In marine settings, decaying wood can generate sulphide which usually attains higher concentrations only in the inner parts of the wood; the sulphide at the surface of the wood is present only occasionally (e.g.…”

“…On the other hand, if wood chips accumulated close to the surface of the sediment they could inhibit the gas exchange between the sediment and the overlying marine water similar to the manner xylophagain fecal pellets imped gas exchange in the sediment around infested wood logs (e.g. Bienhold et al, 2013). We also speculate that in addition to wood, which is the main terrestrial plant material delivered to the sea (West et al, 2011), investigated sandstone bed could initially comprise bark, twigs and leaves which in modern seas can cover the seabed close to the areas rich in vegetation even in relatively deep waters (Wolff, 1979), but are less likely to become fossilized.…”