RATE AND PROCESS OF TUBE PRODUCTION BY THE DEEP-SEA HYDROTHERMAL VENTTUBEWORM RIFTIA-PACHYPTILA

To understand the tube growth process of Riftia pachyptila, morphologi cal aspects of worms and their tubes were studied. In parallel, tube s ecretion experiments were performed on live animals, in pressure aquar ia. Dry weights of the secretions, along with their chitin content (a major component of the tube) were used to quantify tube production. Ou r results show a variation of the gross morphology of the plume and th e trunk of R. pachyptila during its growth and indicate that vestiment um length and tube diameter could be useful indices of individual and tube sizes of R. pachyptila. The presence of clumps of freshly secrete d tube material at the base of the exoskeleton as well as the new obse rvation of bifid tubes allow us to propose a model of tube growth at b oth ends. In this model the tube growth would exhibit a moulting-like step. Bifid shapes may help in space displacement, and the modificatio n of the positioning in height relative to a vent could be used by an individual to modify its access to vent fluid. Tube growth at the apic al end facing the plume has been quantified as a minimal estimate of t he rate of tube production. Experiments performed on repressurized wor ms indicate that 1 mm(2) of worm vestimentum area may secrete more tha n 2 mu g of dry weight tube material per day, leading to a minimum tub e growth rate of 14 cm yr(-1). When compared to other marine ecosystem s, it is obvious that chitin production per unit of area of the the ve nt communities, based on the R. pachyptila alone, are the highest reco rded and similar values were only recorded in polluted freshwater envi ronments.