CIESM Congress 2001, Monaco, article 0023

Rapp. Comm. int. Mer Médit., 36,2001

Introduction

Following the discovery of dense chemosynthetic-based popula-

tions associated with hydrothermal vents in the deep rift system (1)

submersible and remotely operated vehicle investigations discovered

number of seep sites indicating that seeping is a general feature of the

geohydrologic system of continental margins.

Since first discovery of communities in the Gulf of Mexico (2) and

immediatly after in Japan trenches (3) number of sites were described

in continental margins between 400 and 6000m in different geological

contexts (reviewed in Sibuet and Olu - 4) and more recently even till

7326m (5). In all sites, Chemosynthetic-based communities are

restricted to areas where hydrogen sulfide and/or methane rich seeps

out along geological faults.

The food webs of hydrothermal vent and cold seep communities

entirely rely on the production of organic matter via bacterial

chemoautolithotrophy (6), the two main sources of energy in these

zones appear to be sulfide or/and methane (7, 8)

Among these geological contexts, mud volcanoes has been identi-

fied as one of the contexts favorizing to the exploitation by chemosyn-

thetic-based symbioses of cold seeps rich in methane (9).

Results and Discussion

The Anaximender area (southwester Turkey) was explored with the

submersibleNautileduring the French-Dutch M

EDINAUTE

expedition

(1998).

Dense living chemosynthetic-based communities were for the first

time observed at 1700m depth in Mediterranean southwestern to

Turkey.These assemblages occur usually at the top of mud volcanoes

or along fault zones and are associated with methane seeps. Living

individuals were mainly sampled on the top of Kazan mud volcanoe at

1707m (35°25.983N ; 24°33.594E) , large site composed of a mixture

of grey-dark sediment and pieces of calcareus crusts and densily pop-

ulated. The main componant of the community is a lucinid bivalve,

identified as Myrtea sp.. Others living symbiotic bivalves include a

small vesicomyid, Vesycomya sp.and an unknown small mytilid set-

tled on carbonated crusts. Few vestimentiferan tubes with living

worms were also collected on this site. Lying on the heavily reduced

sediment, white-grey bacterial mats were observed as well as many

unknow sea urchins and number of undetermined crabs.

Transversal sections of Myrtea sp.gill filaments observed by TEM

demonstrated them mainly composed by bacteriocytes housing sulfur-

oxidizing type bacteria. This type of symbionts was also observed in

gill cells of Vesicomya sp.as well as in the trophosome of the unde-

termined vestimentiferan worm . The undetermined mytilid appeared

as an additionnal exemple of symbiosis using both reduced sulfide

components and possibly methane as potential source of energy.TEM

observations show that the great majority of the gill cells contains two

distinct morphological types of symbionts. The first type is small

(mean diameter: 0.35 µm) coccoids or short rods and similar to the sul-

fide-oxidizing symbionts observed in B. thermophilus.The second

type are large ( mean diameter: 1.25 µm ) coccoid-shaped bacteria

resembling type I methylotrophs with stacked intracytoplasmic mem-

branes.

13C/12C isotopic ratios clearly enhanced the hypothesis of

chemosynthetic based organic material with values ranging from

–27.7‰ to – 30.5‰ for Myrtea sp, from –29.3‰ to –30.1‰ for

Vesicomya sp. and from –23.6‰ to –26.6‰ for the vestimentiferan

worm, values similar to others symbiotic chemosynthetic-based

bivalves or vestimentiferan worms housing sulfur-oxydizing sym-

bionts and found in different vent or cold seep sites .

The values obtained for the mytilid are more depleted : ranging

from 44.2‰ to -44.6‰ they are in agreement with the presence of

methylotrophic symbionts possibly using methane as energy source.

The 15N/14N isotopic ratios are also in agreement with data obtained

on other bivalves or vestimentiferan worms found in other vent or cold

seep sites ranging from -1.0 to 1.4 ‰ for Myrtea sp., from 0.2 to 0.4‰

for the mytilid, to-1.6 to 1.9‰ for Vesicomya sp.and from -0.8 to

0.2‰ for the vestimentiferan worm.

Conclusion

The results demonstrated for the first time the presence of living

chemosynthetic-based populations associated with ?uids in deep

Mediterranean mud volcanoes . These populations obviously got their

energy either from sufide abundant in reduced sediments of these

zones or from both sediment-sufide and of methane expelled in large

amount in the cold seeps.

References

1 - Jannasch H.W., 1989. Chemosynthetically sustained Ecosystems in

the Deep Sea. In : H.G. Schelgel and B. Bowien eds., Autotrophic bacte-

ria, pp 147-166, Science Techn. Publ. Madison and Springer verlag,

Berlin.

2 - Paull C.K.,W. Ussler III, W.S. Browski and F.N. Spiess, 1985.

Methane-rich plumes on the Carolina continentalrise : Associations with

gas hydrates. Geol.,23 : 89-92.

3 - Laubier L.,S. Ohta and M. Sibuet, 1986. Découverte de communautés

animales profondes durant la campagne franco-japonaise KAIKO de

plongées dans les fosses de subduction autour du Japon. C.R. Acad.Sci.

Paris, III, 303 : 25-29.

4 - Sibuet, M., and K. Olu, Biogeography, biodiversity and ?uid depen-

dance of deep-sea cold seep communities at active and passive margins,

I, II, 45, 517-567, 1998.

5 - Fujikura K, S. Kojima, K. Tamaki,Y. Maki, J. Hunt , T. Okutani,

1999. The deepest chemosynthesis-based community yet discovered from

the hadal zone, 7326m deep, in the Japan Trench.Mar. Ecol. Prog. Ser.,

190 : 17-26.

6 - Jannasch H.W.,and M.J. Mottl,1985. Geomicrobiology of Deep-sea

hydrothermalVents.Science,229 :717-725.

7 - Fisher C.R., 1990. Chemoautotrophic and Methanotrophic symbioses

in marine Invertebrates.Aquat. Scien ces ,2(3-4) :399-436.

8 - Fiala-Médioni A., J. Boulègue, S. Ohta, H. Felbeck and A. Mariotti,

1993. Source of enengy sustaining the Calyptogena populations from

deep trenches in subduction zones off Japan. Deep-sea Res., 40(6) :

1241-1258.

9 - Henry P., X. Le Pichon, S. Lallemant, S. Lance, J. Martin, J.P.

Foucher,A. Fiala-Médioni, N. Guilhaumou, F. Rostek, V. Pranal, and M.

Castrec. 1996. Fluid Flow in and around of a mud volcano field seaward

of the Barbados Accretionary Wedge : Results from Manon Cruise.

J. Geophys. Res.,101,B9: 20297-20323.

# J.P. Foucher ,J. Woodside, J. Mascle, G. De Lange, G. Aloisi, J.L.

Charlou, J.P. Donval, R. Haese, P. Henry, S. De Lint, M. van der Maarel,

G. Nobbe, C. Pierre , R. Pancost.

CHEMOSYNTHESIS-BASED COMMUNITIES ASSOCIATED WITH FLUIDS IN

DEEP MEDITERRANEAN MUD-VOLCANOES

A. Fiala-Medioni

, M. Sibuet

, J.C.Gottschal

,A. Mariotti

and the Medinaut scientific shipboard party #

Observatoire Océanologique, Université P.M. Curie, Banyuls-sur-Mer, France, afiala@obs-banyuls.fr

DRO/EP, Ifremer Brest, Plouzané, France.

Department of Microbiology, University of Groningen, NNHaren, The Netherlands.

Laboratoire de Biogéochimie Isotopique, Université P.M. Curie, Paris,France.

Abstract

Dense living chemosynthetic-based communities were for the first time observed at 1700m depth in Mediterranean southwestern to

Turquia. These assemblages, mainly composed of bacterial mats, tube worms, small bivalve molluscs (Lucinidae, Mytilidae ,

Vesicomyidae) and an Echinidae sea urchin, occur usually at the top of mud volcanoes or along fault zone and are associated with methane

seeps.Tube worms and bivalve molluscs are sustained, through bacterial symbiotic associations, either by sulfide present in the sediments

or by both sediment- sulfide and methane abundant in the seeps.

KeyWords: Eastern Mediterranean Sea, Mud-volcanoes,Chemosynthetic populations