Meteor-Blog 4. August 2008: REGAB Pockmark crowded by life

Planetearth Blog

Does the biodiversity of deep-sea organisms play a role for the climate on Planet Earth? Questions all about marine research will be answered directly aboard of the German research vessel Meteor by cruise leader Prof. Antje Boetius and her crew. In cooperation with the geoportal planeterde.de from 17.08.08 to 24.08.08 they contribute a Science-Blog of METEOR expedition M76/3 GUINECO – MARUM research of fluid and gas seeps on the Westafrican continental margin. Technical highlight of the cruise is the remote-controlled under water robot QUEST4000 by MARUM that will be deployed for taking fauna and sediments samples and conduction of in situ experiments. Go on a dive down to places no other human being has ever seen before: explore the fascinating deep-sea fauna and watch the scientists’ work at gas and fluid seeps deep down on the ocean bottom.

Expedition M76/3b is a collaboration of MARUM – Center for Marine Environmental Sciences at Bremen University and its associated institutes MPI and AWI as well as the French research institute IFREMER and the University of Paris.

More Informationen of the Meteor-Blog, an overview of all contributions to the blog and expedition M76/3B:

4. August 2008 (Author: Karine Olu)

Present Position

“Hello, I am Karine Olu, deep-sea biologist at Ifremer (French Research Institute for the exploration of the sea) in Brest, France. My research, since 15 years, mainly focuses on animal communities living at cold seep ecosystems. This is my fourth cruise in the deep Congo basin, that reveals each time some of its secrets, and the diversity of its deep-sea ecosystems. We had the first dive on the giant pockmark REGAB in the year 2000 with the French ROV Victor 6000 and we were fascinating by the diversity of the landscapes and the very high density of organisms. This site was so exciting that we decided to carry on interdisciplinary research now in a collaborative project with the MARUM of Bremen. On this cruise, we continue sampling fauna and sediment to describe the biodiversity of the pockmark, understand how the different species are distributed according to the heterogeneity of the habitat, and understand how the animals deal with the huge amounts of chemical energy, but also the toxic conditions at seeps.”

Picture 1 : Giant tubeworms belonging to the Siboglinidae family – these may grow up to two meters in length!

REGAB Pockmark crowded by life:

The diversity of the chemosynthetic symbiont-bearing species at the REGAB pockmark

Today we have been working on biological samples retrieved during the last dive. The biomass of cold-seep communities is dominated by large size invertebrates, which host bacterial symbionts in their tissues. The bacteria are able to use reduced compounds (methane, or sulphide) produced at cold seeps and to transfer organic compounds to their host. They belong to two main groups, the bivalves (molluscs with two valve shells) and polychaetes (“hairy” worms) living in tubes. For most of them, symbiosis this is their only way to feed, as they have reduced digestive systems or even none, as in the tubeworms belonging to the Siboglinidae family (picture 1), or for bivalves of the Solemyidae family (picture  2).

Picture 2 : Mussels of the family Solemyidae and several other cold seep organisms are symbiont-bearing species. They inhabit bacteria in their tissues that generate energy from chemical components and this way « feed » their host.

The mussels whose density can reach 1000 individuals per square meter (picture 3) can filter the water for food, like their shallow water counterparts, but our results show that they mainly rely on methane originated carbon. A third group of bivalves living at the REGAB site are “clams” belonging to the families Vesicomyidae (photo: see blog 28.07) and Thyasiridae.

Picture 3 : REGAB Pockmark is crowded by life : up to 1000 individuals may exist per squaremeter in local mussel beds.

They live partially or totally buried in the sediment and have to deal with high sulphide concentration and low oxygen. While the symbionts of mussels mainly use methane, the clam and tubeworm symbionts use sulphide that diffuses into their hosts via the foot of the clams, or by the posterior end of the tubeworm called “roots” which they stick deep into the sediment. The mussels need high methane fluxes and also hard substratum to settle, while the clams prefer soft bottom seafloor and high sulphide levels. Symbiosis is an efficient way for survival: The bivalves can reach 20 cm in length for the mussels (picture 4) and 12 cm for the clams. And the tubeworms grow as high as 2 m!

Picture 4 : Mussels may also grow extremely tall up to 20 centimeters !