BIOLOGY AND ECOLOGY OF THE POMPEII WORM (ALVINELLA-POMPEJANA DESBRUYERES 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 temperatur e probe measurements, temperature time series, and on-board and shore- based chemical analyses based on discrete sampling (pH, H2S, CO2, CH4, S2O32-, Ca, Mg, Cu, Cd? Zn), The microhabitat is characterised by hig h temporal and microscale spatial variability, with temperature values in the range of 20 degrees-45 degrees C at the immediate periphery of tubes but reaching higher, still undetermined, values inside the tube s. 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 biologic al interfaces (tubes and cuticle). Temporal instability possibly also plays an important role in the ability for these worms to colonise suc h an extreme habitat. The functional role of dominant epibiotic bacter ia is discussed in the light of recent biochemical and molecular data: the tubeworm-bacteria system can be considered as a symbiotic entity where carbon is probably metabolised and recycled. Sulphide detoxifica tion occurs by oxidation at the gill level and possibly at the intrace llular haemoglobin level. Heavy metals, ingested or absorbed, are trap ped in spherocrystals and bound to metallothionein-like proteins. Anat omical, physiological and molecular adaptations to hypoxia allow the w orm to successfully colonise the chimneys. A. pompejana lives in an ep hemeral environment and must reproduce and disperse accordingly. It is a gonochoric species that displays a pseucopulatory behaviour allowin g transfer of sperm to female spermathecae, thus avoiding dispersion o f the gametes. The size of the oocytes suggests a lecithotrophic or be nthic development. The population size structure is polymodal, indicat ing discontinuous recruitment. Population genetics data indicate the o ccurrence of a microscale level of population differentiation that doe s 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 in herent to the vents' highly variable conditions. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.