Biology and ecology of the “Pompeii worm” ( Alvinella pompejana Desbruyères and Laubier), a normal dweller of an extreme deep-sea environment: A synthesis of current knowledge and recent developments

Alvinella pompejana, the “Pompeii worm” lives on active hydrothermal edifices at deep-sea vents of the East Pacific Rise. The physical and chemical patterns of its microhabitat were determined from temperature probe measurements, temperature time series, and on-board and shore-based chemical analyses based on discrete sampling (pH, H 2S, CO 2, CH 4, S 2O 2- 3, Ca, Mg, Cu, Cd, Zn). The microhabitat is characterised by high temporal and microscale spatial variability, with temperature values in the range of 20°–45°C at the immediate periphery of tubes but reaching higher, still undetermined, values inside the tubes. The difference observed between in vitro temperature limits for the stability of biomolecules and metabolic rates, and suggested in situ conditions seems to indicate a significant protective role of biological interfaces (tubes and cuticle). Temporal instability possibly also plays an important role in the ability for these worms to colonise such an extreme habitat. The functional role of dominant epibiotic bacteria is discussed in the light of recent biochemical and molecular data: the tube-worm–bacteria system can be considered as a symbiotic entity where carbon is probably metabolised and recycled. Sulphide detoxification occurs by oxidation at the gill level and possibly at the intracellular haemoglobin level. Heavy metals, ingested or absorbed, are trapped in spherocrystals and bound to metallothionein-like proteins. Anatomical, physiological and molecular adaptations to hypoxia allow the worm to successfully colonise the chimneys. A. pompejana lives in an ephemeral environment and must reproduce and disperse accordingly. It is a gonochoric species that displays a pseucopulatory behaviour allowing transfer of sperm to female spermathecae, thus avoiding dispersion of the gametes. The size of the oocytes suggests a lecithotrophic or benthic development. The population size structure is polymodal, indicating discontinuous recruitment. Population genetics data indicate the occurrence of a microscale level of population differentiation that does not increase with increasing geographical distances, thus suggesting the occurrence of a metapopulation-like system and/or the possibility that enzyme loci evolve under stabilising selective driving forces inherent to the vents’ highly variable conditions.