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Marine Ecology Progress Series

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MEPS 405:187-201 (2010)  -  DOI:

Mixotrophy in the deep sea: a dual endosymbiotic hydrothermal mytilid assimilates dissolved and particulate organic matter

Virginie Riou1,2,*, Ana Colaço1, Steven Bouillon2,5, Alexis Khripounoff3, Paul Dando4, Perrine Mangion2, Emilie Chevalier2, Michael Korntheuer2, Ricardo Serrão Santos1, Frank Dehairs2

1IMAR-University of the Azores, Department of Oceanography and Fisheries, 9901-862 Horta, Portugal
2Earth System Sciences Group, Department of Analytical and Environmental Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
3Ifremer, Centre de Brest, DEEP/LEP, 29280 Plouzané, France
4Marine Biological Association of the UK, Plymouth PL1 2PB, UK
5Katholieke Universiteit Leuven, Department of Earth and Environmental Sciences, 3001 Heverlee, Belgium

ABSTRACT: Bathymodiolus azoricus mussels thrive 840 to 2300 m deep at hydrothermal vents of the Azores Triple Junction on the Mid-Atlantic Ridge. Although previous studies have suggested a mixotrophic regime for this species, no analysis has yet yielded direct evidence for the assimilation of particulate material. In the present study, tracer experiments in aquaria with 13C- and 15N-labelled amino acids and marine cyanobacteria demonstrate for the first time the incorporation of dissolved and particulate organic matter in soft tissues of vent mussel. The observation of phytoplanktonic tests in wild mussel stomachs highlights the occurrence of in situ ingestion of sea-surface-derived material. Particulate organic carbon fluxes in sediment traps moored away from direct vent influence are in agreement with carbon export estimates from the surface ocean above the vents attenuated by microbial degradation. Stable isotope composition of trapped organic matter is similar to values published in the literature, but is enriched by +7‰ in 13C and +13‰ in 15N, relative to mussel gill tissue from the Menez Gwen vent. Although this observation suggests a negligible contribution of photosynthetically produced organic matter to the diet of B. azoricus, the tracer experiments demonstrate that active suspension-feeding on particles and dissolved organic matter could contribute to the C and N budget of the mussel and should not be neglected.

KEY WORDS: Bathymodiolus azoricus · Particulate and dissolved material · Nitrogen and carbon assimilation · Deep sea · Hydrothermal vent · Mussel

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Cite this article as: Riou V, Colaço A, Bouillon S, Khripounoff A and others (2010) Mixotrophy in the deep sea: a dual endosymbiotic hydrothermal mytilid assimilates dissolved and particulate organic matter. Mar Ecol Prog Ser 405:187-201.

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