Reproduction

Hydrothermal vents are ephemeral ecosystems; specific sites usually remain active for only a few years due to the geothermal nature of their formation (Hessler et al., 1988).  Vent sites are also distributed in patches along the mid ocean ridges where they form, spaced hundreds of kilometers apart (Mullineaux et al., 2000).  For these reasons, R.pachyptila is required to be able to spread their offspring long distances in order to reach new sites, they also need to be able to colonise new sites quickly in order to grow and reproduce before the flow of venting fluid stops.  Not all aspects of the reproductive strategy of R.pachyptila  is known, due to the fact that there has been no success of larval capture in the wild (Dworkin et al., 2006).

R.pachyptila populations are made up of separate sexes.  Release of gametes occurs simultaneously in localised areas of tubeworm populations, presumably by pheromonal signals between worms in a small area.  The tubeworms eject their gametes into the water by quickly retracting into their tubes.  Each release creates a cloud of gametes 10 to 15cm in size (Van Dover, 1994).  Male sperm aggregate into bundles, containing hundreds of individual cells.  The sperm of male tubeworms are effective swimmers, which helps the bundles to reach a female.  After reaching a female tubeworm, sperm bundles attach to the epidermis by the acrosome (the head of the sperm cell) (Cary et al., 1989).  After attaching to the female, the eggs stored in the female’s vestimental chamber are released.  Fertilisation can happen either internally prior to the release of the eggs, or externally subsequent to spawning.  Eggs are expelled by the female into the water where they are carried by the water currents away from the site of fertilisation (Van Dover, 1994).

Zygotes of R.pachyptila develop into free swimming lecithotrophic larvae (Marsh et al., 2001).  Lecithotrophic larvae do not feed while in their larval stage, they instead rely on yolk reserves for nourishment (McEdward, 1995).  The tubeworm trocophore larvae propel themselves and control their movement in the water using bands of cilia (McEdward, 1995). Larvae of R.pachyptila survive for around 38 days before settling, acquiring bacterial symbionts from the environment and metamorphosing into the adult body form if a suitable habitat and substrate is found. Depending on the current speed in the ocean, the tubeworm larvae can travel long distances, up to 100 kilometres (Figure 6) (Marsh et al., 2001).  It is important to note however that these results were calculated as part of a model and dispersal potential of R.pachyptila may be different in situ.

Figure 3. Maximum dispersal distance and percentage of survivors of R.pachyptila larvae of each specific lifespan.  From Marsh et al. (2001).

Figure 6. Maximum dispersal distance and percentage of survivors of R.pachyptila larvae of each specific lifespan. From Marsh et al. (2001).

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