Page path:

21.01.2013 Wood on the sea­floor

 
Wood on the seafloor- an oasis for deep-sea life

Trees do not grow in the deep sea, nev­er­the­less sunken pieces of wood can de­velop into oases for deep-sea life - at least tem­por­ar­ily un­til the wood is fully de­graded. A team of Max Planck re­search­ers from Ger­many now showed how sunken wood can de­velop into an at­tract­ive hab­it­ats for a vari­ety of mi­croor­gan­isms and in­ver­teb­rates. By us­ing un­der­wa­ter ro­bot tech­no­logy, they con­firmed their hy­po­thesis that an­im­als from hot and cold seeps would be at­trac­ted to the wood due to the activ­ity of bac­teria, which pro­duce hy­dro­gen sulf­ide dur­ing wood de­grad­a­tion.

Many of the an­im­als thriv­ing at hy­dro­thermal vents and cold seeps re­quire spe­cial forms of en­ergy such as meth­ane and hy­dro­gen sulf­ide emer­ging from the ocean floor. They carry bac­terial sym­bionts in their body, which con­vert the en­ergy from these com­pounds into food. The vents and seeps are of­ten sep­ar­ated by hun­dreds of kilo­met­ers of deep-sea desert, with no con­nec­tion between them.

For a long time it was an un­solved mys­tery how an­im­als can dis­perse between those rare oases of en­ergy in the deep sea. One hy­po­thesis was that sunken whale car­casses, large dead al­gae, and also sunken woods could serve as food source and tem­por­ary hab­itat for deep-sea an­im­als, but only if bac­teria were able to pro­duce meth­ane and sul­fur com­pounds from it.
Col­on­iz­a­tion of wood in the deep sea. (© Bi­en­hold et al., PLoS ONE 8(1): e53590).
To tackle this ques­tion, the team de­pos­ited wood logs on the East­ern Medi­ter­ranean sea­floor at depths of 1700 meters and re­turned after one year to study the fauna, bac­teria, and chem­ical mi­cro­gradi­ents.
“We were sur­prised how many an­im­als had pop­u­lated the wood already after one year. The main col­on­izers were wood-bor­ing bi­valves of the genus Xy­lo­phaga, also named “ship­worms” after their shal­low-wa­ter coun­ter­parts. The wood-bor­ing Xy­lo­phaga es­sen­tially con­sti­tute the van­guard and pre­pare the hab­itat for other fol­low­ers,” Bi­en­hold said. „But they also need as­sist­ance from bac­teria, namely to make use of the cel­lu­lose from the wood, which is dif­fi­cult to di­gest.”
The team of re­search­ers ob­served that the wood-bor­ing bi­valves had cut large parts of the wood into smal­ler chips, which were fur­ther de­graded by many other or­gan­isms. This activ­ity led to the con­sump­tion of oxy­gen, en­abling the pro­duc­tion of hy­dro­gen sulf­ide by sulfate-re­du­cing mi­croor­gan­isms. And in­deed, the re­search­ers also found a mus­sel, which is typ­ic­ally only found at cold seeps or sim­ilar en­vir­on­ments where it uses sul­fur com­pounds as an en­ergy source. “It is amaz­ing to see how deep-sea bac­teria can trans­form for­eign sub­stances such as wood to provide en­ergy for cold-seep mus­sels on their jour­ney through the deep ocean”, said Antje Boe­t­ius, chief sci­ent­ist of the ex­ped­i­tion. Fur­ther­more, the re­search­ers dis­covered un­known spe­cies of deep-sea worms, which have been de­scribed by taxo­nomic ex­perts in Ger­many and the USA. Thus, sunken woods do not only pro­mote the dis­persal of rare deep-sea an­im­als, but also form hot­spots of biod­iversity at the deep sea­floor.

Manfred Schlösser


This study was part of the Ger­man-French pro­ject DI­WOOD, which is sup­por­ted by the Max Planck so­ci­ety and the CNRS. Fur­ther sup­port came from the EU Pro­jects HER­MES (6 FP) and HER­MI­ONE (7 FP).
One of the wood ex­per­i­ments after one year at the sea­floor. Wood-bor­ing bi­valves of the genus Xy­lo­phaga had pop­u­lated the wood.
 
Back to Top