Prolonged recovery time after eruptive disturbance of a deep-sea hydrothermal vent community.

Deep-sea hydrothermal vents are associated with seafloor tectonic and magmatic activity, and the communities living there are subject to disturbance. Eruptions can be frequent and catastrophic, raising questions about how these communities persist and maintain regional biodiversity. Prior studies of frequently disturbed vents have led to suggestions that faunal recovery can occur within 2-4 years. We use an unprecedented long-term (11-year) series of colonization data following a catastrophic 2006 seafloor eruption on the East Pacific Rise to show that faunal successional changes continue beyond a decade following the disturbance. Species composition at nine months post-eruption was conspicuously different than the pre-eruption 'baseline' state, which had been characterized in 1998 (85 months after disturbance by the previous 1991 eruption). By 96 months post-eruption, species composition was approaching the pre-eruption state, but continued to change up through to the end of our measurements at 135 months, indicating that the 'baseline' state was not a climax community. The strong variation observed in species composition across environmental gradients and successional stages highlights the importance of long-term, distributed sampling in order to understand the consequences of disturbance for maintenance of a diverse regional species pool. This perspective is critical for characterizing the resilience of vent species to both natural disturbance and human impacts such as deep-sea mining.

The early conversion of deep-sea wood falls into chemosynthetic hotspots revealed by in situ monitoring.

Wood debris on the ocean floor harbor flourishing communities, which include invertebrate taxa thriving in sulfide-rich habitats belonging to hydrothermal vent and methane seep deep-sea lineages. The formation of sulfidic niches from digested wood material produced by woodborers has been known for a long time, but the temporal dynamics and sulfide ranges encountered on wood falls remains unknown. Here, we show that wood falls are converted into sulfidic hotpots, before the colonization by xylophagaid bivalves. Less than a month after immersion at a depth of 520 m in oxygenated seawater the sulfide concentration increased to millimolar levels inside immersed logs. From in situ experiments combining high-frequency chemical and video monitoring, we document the rapid development of a microbial sulfur biofilm at the surface of wood. These findings highlight the fact that sulfide is initially produced from the labile components of wood and supports chemosynthesis as an early pathway of energy transfer to deep-sea wood colonists, as suggested by recent aquarium studies. The study furthermore reveals that woodborers promote sulfide-oxidation at the periphery of their burrows, thus, not only facilitating the development of sulfidic zones in the surrounding of degraded wood falls, but also governing sulfur-cycling within the wood matrix.

Colonization of organic substrates deployed in deep-sea reducing habitats by symbiotic species and associated fauna.

In this study, our goal was to test whether typical vent/seep organisms harbouring symbionts or not, would be able to settle on organic substrates deployed in the vicinity of chemosynthetic ecosystems. Since 2006, a series of novel standardized colonization devices (CHEMECOLI: CHEMosynthetic Ecosystem COlonization by Larval Invertebrates) filled with three types of substrates (wood, alfalfa and carbonate) have been deployed in different types of reducing habitats including cold seeps in the eastern Mediterranean, a mud volcano in the Norwegian Sea, and hydrothermal vents on the Mid-Atlantic Ridge for durations of 2 weeks to 1 year. For all deployments, highest species diversities were recovered from CHEMECOLIs filled with organic substrates. Larvae from species associated with thiotrophic symbionts such as thyasirid, vesicomyid and mytilid bivalves, were recovered in the eastern Mediterranean and at the Mid-Atlantic Ridge. At the Haakon Mosby Mud Volcano, larvae of symbiotic siboglinids settled on both organic and carbonate substrates. Overall, novel colonization devices (CHEMECOLI) filled with organic substrates attracted both fauna relying on chemosynthesis-derived carbon as well as fauna relying on heterotrophy the latter being opportunistic and tolerant to sulphide.

Biotic and abiotic controls on iron oxyhydroxide formation in the gill chamber of the hydrothermal vent shrimp Rimicaris exoculata.

A unique feature of the shrimp, Rimicaris exoculata, from the Rainbow hydrothermal vent field is the abundance of iron oxyhydroxides in its branchial chamber. These minerals accumulate throughout the molting cycle and are intimately associated with the shrimps' epibiotic microflora. In this study, an enhancement of the iron oxidation rate through shrimp swarms in the vicinity of vents is highlighted. This process is sustained by the high molting frequency of the shrimp, and potentially has large biogeochemical and ecological consequences for the associated hydrothermal ecosystem. The calculated rate for abiotic (homogeneous and heterogeneous) iron oxidation suggests that autocatalytic oxidation is the predominant reaction pathway leading to the accumulation of iron oxyhydroxides throughout the molting cycle. The occurrence of iron-oxidizing bacteria is not excluded, but their growth is most probably restricted to the first molting stage when competition with the abiotic iron oxidation is low. The influence of epibiont activity on local oxygen conditions and on the surface properties of the formed mineral, combined with the position of the shrimp in the hydrothermal mixing gradient, is expected to drive the relative contribution of abiogenic and biogenic iron oxidation.