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Implications of cross-axis flow for larval dispersal along mid-ocean ridges

Introduction : Dispersal processes play an important role in the structure and dynamics of many terrestrial and marine communities, and they are especially critical in deep-sea hydrothermal vent ecosystems. These systems are patchy and transient, and most of the species inhabiting them cannot survive elsewhere, so successful dispersal (usually via a larval stage) is essential for maintaining viable populations and species ranges. To understand the mechanisms of larval dispersal, we need to know larval life spans and the transport dynamics of deep-water flows near vent habitats. When these values are measured for a species in a given region, a maximum dispersal distance can be calculated and compared to the geographic spacing between vent fields in that region. This approach gives a first-order answer to the questions of how far a larva can disperse and whether a species has the potential to migrate between any two given vent sites. However, to understand the effects of dispersal on population dynamics, gene flow and population genetic structure, we need to know the number of migrants among sites. This calculation requires estimates of fecundities and mortality rates that are very difficult to verify for vent species (e.g., Chevaldonne et al., 1997), and are outside the scope of our study. The objective of the present study is to focus on the first-order question of how far larvae of a given lifespan can disperse in the flow environments near vent sites at different mid-ocean ridges. We follow the approach that Marsh et al. (2001) used to calculate dispersal potential of larvae of the vestimentiferan tubeworm Riftia pachyptila Jones, 1981, near 9°N on the East Pacific Rise (EPR). They conducted physiological measurements on larvae cultured at ambient deep-sea pressure to calculate a R...