Abstract

Since the discovery of sulfide-oxidizing organisms associated with vegetal debris collected in the deep sea, these sunken woods are suspected to release sulfide during their degradation in the seawater, similarly to what was observed on whale falls. Sulfides could be used by the organisms for their development on the decomposing wood. We were concerned by sunken woods in mangrove swamp, which is provided in vegetal debris by the close mangrove vegetation (Rhizophora mangle). This environment allows quite easy realization of chemical in situ measurements. Experimental immersions of mangrove branches were realised in the site Manche-à-Eau of the mangrove swamp of Guadeloupe in order to monitor the evolution of chemical parameters of the wood surface: pH and levels of hydrogen sulphide. This chemical monitoring realised with autonomous probes revealed sulfide enrichment on the wood surface. Sulfide contents reaching almost millimolar levels were measured on the wood surface, while no sulfide was detectable in the surrounding seawater. These levels were roughly reached after four days of wood immersion and can maintain several weeks. In order to determine if these sulfide levels could sustain the installation of a sulfide-oxidizing fauna associated with the sunken woods, a biological monitoring was also realized. The first organisms to colonise the wood were some protozoans ciliates. Among them, some bacterial ectosymbioses were observed (notably in Zoothamnium niveum and Vorticella sp.) using scanning electron microscope observations and in situ hybridization tecniques. These organisms testify of the relation between the sulfide released from the decomposing wood and the colonization of this wood.

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