Spatial and temporal variations of recruitment in the tube worm Riftia pachyptila on the East Pacific Rise (9°50'N and 13°N)

Abstract

The giant vestimentiferan tubeworm Riftia pachyptila is one of the most abundant and ecologically important species at deep-sea hydrothermal vents along the East Pacific Rise (EPR). Clumps of R. pachyptila could indeed be viewed as one of the most frequent habitats for the fauna typifying the eastern Pacific hydrothermal vent sites and thus deserve specific attention, as their dynamics are likely to control the spatial and temporal evolution of numerous vent species. As a consequence, population structure and recruitment of R. pachyptila were studied from samples taken at different vent localities during 2 EPR surveys in 1996 and 1997. In 1996, 3 samples were collected within and between the hydrothermal vent fields 13°N and 9°50' N to assess the spatial coherence of recruitment. In 1997, a huge number of additional specimens were collected at 9°50' N from a single vent site at 3 successive dates over 22 d to determine how growth rate may affect the temporal variability of population structure at a small spatial scale. Size-frequency analyses were performed using the vestimentum width as a biometric index. Inter-site comparisons revealed that size-frequency distributions did not differ significantly within a vent field suggesting the synchronisation of recruitment locally (i.e. a few km). By contrast, population structure strongly differed between the 2 vent fields in response to local variations in time of larval supply and/or reproductive activity. The size-frequency histograms of the 3 samples collected in 1997 displayed a regular polymodal structure reflecting a discontinuous recruitment in time. The presence of a large number of small individuals attached to the tube of conspecific larger ones suggested that biological cues associated with Riftia may promote habitat selection by settlers. Differences between the modal vestimentum width of each population 'cohorts' from the 3 temporal samples were significant and could result from either a growth rate heterogeneity in response to local environmental variations or to population ageing. According to this 2nd assumption, growth rate was estimated from the evolution of the 5 'cohorts' found over 22 d. Our data suggested that R. pachyptila exhibits: (1) a high yearly tube growth rate (estimated to about 160 cm yr

Spatial and temporal population genetics at deep-sea hydrothermal vents along the East Pacific Rise and Galapagos Rift

“…Additionally, local vent populations have transient lifespans on the same timescale as faunal lifespans, resulting from frequent extinction and recolonization processes (Thiébaut et al 2002). Geophysical and geochemical instability at vents may serve to (1) create population bottlenecks-increasing genetic drift and reducing metapopulation effective size-and to (2) increase genetic differentiation between vent populations towards the fixation of alleles.…”

“…Recruitment lacks periodicity and is discontinuous, but settlement events can be frequent (e.g., 8 to 20 d) (Thiébaut et al 2002). Once established, tube growth rates may exceed 85 to 160 cm/yr , Thiébaut et al 2002. While large worms may only inhabit one to two thirds of their total tube length (Govenar et al 2004), Riftia is still considered one of the fastest growing organisms on Earth, out-competing or over-growing the smaller tubeworm species,…”

“…‡, not reported. References: (1) France et al 1992; (2) ; (3) Black et al 1998; (4) Craddock et al 1995b; (5) (6) Karl et al 1996; (7) (8) Jollivet et al 1995a(9) Marsh et al 2001(10) Riftia has separate sexes (Jones 1980), with a nearly equal ratio of males to females (Thiébaut et al 2002), and is highly fecund (Cary et al 1989); up to 700,000 mature eggs have been observed in Riftia's ovisac (Young 2003). Eggs are small, yolky, lipid-rich (Cary et al 1989), and near-neutrally buoyant .…”

“…As colonization occurs within a year or two of newly available habitat, it is considered likely that a pool of larvae is maintained in the water column above vents , Govenar et al 2004. Recruitment lacks periodicity and is discontinuous, but settlement events can be frequent (e.g., 8 to 20 d) (Thiébaut et al 2002). Once established, Riftia grows quickly and out-competes or overgrows the smaller tubeworm species, Tevnia jerichonana, first to colonize new vents , Thiébaut et al 2002).…”

“…This species has separate sexes (Jones 1980), with roughly equal ratio of males to females (Thiébaut et al 2002), and is highly fecund (Cary et al 1989); up to 700,000 mature eggs have been observed in Riftia's ovisac (Young 2003).…”