Deep-sea wood is the term for wood which sinks to the ocean floor. These wood-falls develop

deep sea The deep sea is broadly defined as the ocean depth where light begins to fade, at an approximate depth of 200 metres (656 feet) or the point of transition from continental shelves to continental slopes. Conditions within the deep sea are a combin ...

ecosystems. Deep-sea wood supports unique forms of deep sea community life including chemo-synthetic

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. Sources of carbon for these deep sea ecosystems are not limited to sunken wood, but also include

kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwat ...

and the remains of

whales Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...

. Much of what is known about deep-sea wood is obtained from experiments by marine biologists, in which wood is forced to the bottom of the ocean for a set amount of time and is then collected later for sampling.

Organisms present

Wood boring bivalves

Colonization experiments revealed the presence of wood boring bivalves that belong to the subfamily Xylophagainae, such as ''Xylophaga dorsalis'', or other species recently described from deep-sea canyons. They range in shell size from 1-10mm. These bivalves are able to digest wood with the help of symbiotic bacteria in their gills.

Chemosyntheic fauna

Chemosyntheic muscles identified as ''Idas modiolaeformis'' were also found in deep sea wood when organic matter settled for at least one year. They are slightly smaller than the bivalves found and range in length from 1-6mm.

Other organisms

A variety of deep-sea crabs and sea urchins seemed to also be chemically attracted to the wood. There are numerous species of snail that have been discovered on the wood, along with predatory worms and small crustaceans. Their attraction to the wood may be attributed to its bacterial inhabitants serving as a base organism for deep-sea life, with the potential to feed on microorganisms, or other inhabitants of the wood.

Fungal communities

Fungi are the major degraders of

lignocellulose Lignocellulose refers to plant dry matter (biomass), so called lignocellulosic biomass. It is the most abundantly available raw material on the Earth for the production of biofuels. It is composed of two kinds of carbohydrate polymers, cellulose a ...

in aquatic environments. In aerobic terrestrial environments, a majority of cellulose breakdown is broken down by

wood-decay fungi A wood-decay or xylophagous fungus is any species of fungus that digests moist wood, causing it to rot. Some species of wood-decay fungi attack dead wood, such as brown rot, and some, such as ''Armillaria'' (honey fungus), are parasitic and col ...

commonly and collectively known as white rot and soft rot. Complex enzymes are secreted by the various fungi, converting cellulose into a carbon form that can be utilized by the fungus, and subsequently any organism up the food chain.

Bacterial communities

Bacteria also contribute to the digestion of deep-sea wood, using an alternative method from that of fungi. In order to classify bacteria present on deep-sea wood, a variety of different techniques are employed. First, biomass allows scientists to quantify the amount of bacterial growth on a sample. Then DNA extraction and Automated Ribosomal Intergenic Spacer analysis (ARISA) can be used to identify the strains of bacteria present that are most dominant, and the ones that are present. While ''Gammaproteobacteria'' dominated the composition of bacteria found on freshly submerged wood, many other bacterial strains populated in response to colonization of the aforementioned wood-boring ''Xylophaga'', which take the large chunks of wood and convert them into fine chips and fecal matter. These processed forms of carbon lead to the growth of many other marine bacteria including ''Alphaproteobacteria'', ''Flavobacteria'', ''Actinobacteria'', ''Clostridia'', and ''Bacteroidetes''.

Wood degradation

Presence of anaerobes

The presence of ''Clostridia'', obligate

anaerobes An anaerobic organism or anaerobe is any organism that does not require molecular oxygen for growth. It may react negatively or even die if free oxygen is present. In contrast, an aerobic organism (aerobe) is an organism that requires an oxygenate ...

suggests that the process of degrading the deep-sea wood may create oxygen-free environments for these bacteria to survive in.

Sulfur reducing bacteria

Many bacterial strains that were found on deep-sea wood were

sulfur-reducing bacteria Sulfur-reducing bacteria are microorganisms able to reduce elemental sulfur (S0) to hydrogen sulfide (H2S). These microbes use inorganic sulfur compounds as electron acceptors to sustain several activities such as respiration, conserving energy an ...

, meaning they obtain energy from reducing elemental sulfur, instead of traditionally using the sun for energy like almost all other organisms. Marine biologists suggest they may contribute to the breakdown of cellulose from the wood.

Variability of organisms

The species of wood that falls to the ocean floor produces variability in the organisms present on it. There is also natural viability between organisms found on the same species of tree, which promotes to deep-sea diversity. In fact, a study by marine biologists showed bacterial communities were approximately 75% dissimilar, even as similar logs of the same tree species were placed within the same 500 m² area.

References

{{reflist Aquatic ecology Wood by type Oceanographical terminology