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which normal embryonic/larval development occurs, but by 1) adult temperature
tolerances, 2) temperatures needed for growth or spawning, or 3) hydrographic
features that limit larval settlement and juvenile survival.
Data from experiments carried out by Tyler et al. (2000) showed that the
embryonic and larval stages of the Antarctic echinoid Sterechinus neumayeri (Müller)
are capable of surviving low temperatures in surface waters, but only tolerate higher
pressures when water column temperatures are > 0° C. They infer that the larvae of S.
neumayeri might be capable of penetrating the deep sea through the action of
formation of Antarctic Bottom Water in the Weddell Sea, since this pattern of
temperature increase is seen during deep water formation.
Only one experiment has been carried out onto pressure tolerances of embryos
the bathyal asteroid species Plutonaster bifrons (Wyville Thomson) (Young et al.
1996a). The greatest percentage of embryos developing normally occurred at
pressures equivalent to 2000 m depth, the depth at which the species is most common.
No normal development occurred at a pressure corresponding to 3000 m depth.
Therefore, embryonic tolerances could determine the bathymetric limits of
distribution for this species.
5.2- Effect of hydrodynamic mechanisms on larval dispersal
Developmental mode is not the only factor that might determine dispersal
distance, but larval dispersal patterns depend also on hydrodynamic mechanisms and
such mechanisms may be different in distinct regions. Therefore, larval dispersal
patterns vary between populations according to the relative importance of water
advection and diffusion at a local scale. The flow of water in the deep sea is still not
fully understood compared to the surface circulation. Therefore, in most cases, it is
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