Population structure and recruitment in mytilid bivalves from the Lucky Strike and Menez Gwen hydrothermal vent fields (37°17'N and 37°50'N on the Mid-Atlantic Ridge)

Abstract

Population structure and recruitment pattern of undescribed mytilid bivalves that dominate the animal communities associated with vents of the Lucky Stnke and Menez Gwen hydrothermal vent fields (37" 17' N and 37" 50' N on the Mid-Atlantic Ridge) were studled from size-frequency analyses. Intra-site comparisons reveal that length-frequency distributions differ significantly from one location to the other. This spatial segregation of the sizes could be due to spatio-temporal variability in environmental conditions and to intraspecific competition processes, especially adult-larval interactions (competition for space and food resources, intraspecific larviphagy) that could prevent larvae from settling on surfaces covered by adults. A modal decomposition analysis was conducted after pooling samples collected from different locations at the same site. Polymodal structure of length-frequency distributions indicates that recruitment is likely discontinuous in time. The presence of postlarvae in each population of the Lucky Strike vent field suggests that a recruitment event took place just before sampling in June 1994, and that mytilid recruitment is synchronized between sites, which is confirmed by the comparison of modal values. Length-frequency distribution of the Menez Gwen mytilid population displays similar modal values, especially for the smallest mode. This suggests a synchronization of the recruitment between the 2 vent fields, which are separated by a distance of 60 km. No seasonal pattern in recruitment could be Identified although newly recruited individuals were observed in June 1993 on Lucky Strike sites.

Fossil evidence for serpentinization fluids fueling chemosynthetic assemblages

“…S4). The shells range in length from 5 mm to 84 mm, which is comparable to living B. azoricus shells from high-temperature hydrothermal vent fields on the MAR (51). Very few of the Ghost City mussel shells are fragmented, and quite a few specimens have articulated valves, with a ratio of 3.6 disarticulated to articulated shells (n ¼ 73).…”

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

“…This interval was chosen according to 3 criteria: (1) most size classes must have at least 5 individuals; (2) the number of adjacent empty classes must be minimised; and (3) the interval has to be larger than the error on measurements. Size-frequency histograms were smoothed using a weighted moving average at the 3rd order to rule out spurious peaks (Frontier & Pichod-Viale 1991, Zal et al 1995, Comtet & Desbruyères 1998, Jollivet et al 2000. Modal decomposition of size-frequency histograms was performed using the NORMSEP program (Tomlinson 1971) adapted by Gros & Cochard (1978), assuming a Gaussian distribution of vestimentum width within each cohort.…”

“…Population structures have been assessed through size-frequency analysis for polychaetes and bivalves, providing information on the recruitment patterns of hydrothermal species and mechanisms by which populations renew or are founded. Discontinuous recruitment has been reported for most species studied to date including the ampharetid polychaete Amphisamytha galapagensis (McHugh & Tunnicliffe 1994), the alvinellid polychaetes Alvinella pompejana, A. caudata, Paralvinella grasslei and P. palmiformis (McHugh 1989, Jollivet 1993, Zal et al 1995, serpulid worms and the vestimentiferan Tevnia jerichonana (Jollivet 1993), mytilid bivalves and polynoid commensals (Comtet & Desbruyères 1998, Jollivet et al 2000. Conversely, McHugh (1989) hypothesised a continuous recruitment of the polychaete Paralvinella pandorae.…”

“…For Paralvinella grasslei, Zal et al (1995) hypothesised that tidal signal, which is clearly periodic in the hydrothermal ecosystem, is the most likely external factor coordinating the reproductive cycle of individuals within vent sites and fields. Conversely, Comtet & Desbruyères (1998) suggested that recruitment of mytilid bivalves on the Azorean triple junction may be synchronised between 2 vent fields separated by a distance of 60 km, and proposed that pelagic fluxes could trigger the emission of gametes and/or the settlement of larvae.…”

Rapid colonisation by nematodes on organic and inorganic substrata deployed at the deep-sea Lucky Strike hydrothermal vent field (Mid-Atlantic Ridge)

“…The Eiffel Tower edifice is a well-defined active edifice 11 m high and one of the mostvisited sites within the Lucky Strike vent field. It has been the focus of ecological research over the last ten years (e.g., Van Dover et al 1996;Comtet and Desbruyeres 1998;Desbruyères et al 2001;Cuvelier et al 2009;Cuvelier et al 2011a;Cuvelier et al 2012;Sarrazin et al in press;Matabos et al in press), and also recently in regards to short-term ) and long-term (Cuvelier et al 2011b) temporal variation studies.…”