Stepping Stones

The stepping stone hypothesis (Smith et al., 1989) suggests that whale fall ecosystems could be used as a middle ground for faunal dispersal between the chemosynthetic communities of hydrothermal vents and cold seeps. However, Tunnicliffe and Juniper (1990), rejected the hypothesis because of the absence of truly endemic vent species such as vestimentiferan tubeworms at whale fall sites.  Feldman et al. (1998) identified the presence of the vestimentiferan tube worm Escarpia spicata, supporting the stepping stone hypothesis. Species with strong taxomic and functional similarities at hydrothermal vents, cold seeps and whale falls have been identified (Bennett et al., 1994). Also, species dispersal from whale fall islands to hydrothermal vents has been observed, regardless of a 1800km geographical separation (Bennett et al., 1994; Smith et al., 2003).

The irregular nature of whale fall events suggests that the stepping stone hypothesis, although possible, is unlikely. However, there must be instances where a whale fall has occurred in close enough proximity to a vent site to provide a bridge for the crossover of species. There is no certainty in regards to where a whale will fall, therefore, there must also be other explanations for fauna dispersal among chemosynthetic communities. Perhaps ocean circulation patterns, hydrodynamics and current regimes are responsible for the dispersion of vent larvae without using whale fall events as an intermediate step (Marsh et al., 2001; Van Dover et al., 2002).

There are also many species present at whale falls which are absent from vent and seep sites. Some of these species may be “whale fall specialists”.

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